Curious if Fox has any plans to remove or substantially reduce the bandwidth allocated to null packets on their network feed to affiliates for the Super Bowl?

Anything is possible, but this is unlikely.

new to HDTV, can you explain the null packets for me?

Fox inserts a stream of null packets at the network level, so those affiliates that have subchannels can simply strip off the null packets and insert their secondary channel. Unfortunately this causes the PQ to suffer for EVERYBODY, even if your local affiliate does not multicast.

From the image below, you can see an example of a typical Fox NFL game where the null packets are taking ~7Mbps of the overall bandwidth available. In this example, the HD viewer is getting a 11.48Mbps quality picture, instead of a full 19Mbps quality picture.

http://img231.imageshack.us/img231/5558/wjwvikingspackersotait9.th.png (http://img231.imageshack.us/my.php?image=wjwvikingspackersotait9.png)

The null packet stream is the green bar marked "0x1FFF". It is a variable bit rate, and goes up and down depending on the level of action in the main game.

From the image below, you can see an example of a typical Fox NFL game where the null packets are taking ~7Mbps of the overall bandwidth available. In this example, the HD viewer is getting a 11.48Mbps quality picture, instead of a full 19Mbps quality picture.

You failed to mention that FOX uses variable bit rate shaping, meaning if the picture doesn't need full bandwidth, it doesn't send full bandwidth, only what is needed at that moment. During NFL action shots, the bandwidth goes close to 16 mbs and when no action or still picture, it will drop to around 10 mbs, which is the picture you show here. No action, steady camera.

And no, I don't expect anymore bandwidth than the 16 max that is used now for the SB because some FOX stations have other networks like CW and MNT as subchannels and they can't just turn them off because it is the SB.

I'm not going to complain about 16 mbs....when some of my locals are running 2 or 3 subchannels.

I've seen little in the way of artifacts on Fox's HD network since they upped the network bitrate so I don't think it's really necessary. It shouldn't make the picture noticeably sharper.

Fox already provides multiple feeds of the same show for different regions, so there's theoretically nothing preventing them from providing one feed at 18Mbit/s CBR for the stations that aren't multicasting and one at the standard 15.5 max VBR for everyone that is. I won't pretend to know what Fox is planning to do, but given his track record, I wouldn't bet against anything Ken H says.

You failed to mention that FOX uses variable bit rate shaping, meaning if the picture doesn't need full bandwidth, it doesn't send full bandwidth, only what is needed at that moment. During NFL action shots, the bandwidth goes close to 16 mbs and when no action or still picture, it will drop to around 10 mbs, which is the picture you show here. No action, steady camera.

And no, I don't expect anymore bandwidth than the 16 max that is used now for the SB because some FOX stations have other networks like CW and MNT as subchannels and they can't just turn them off because it is the SB.
Just for the sake of asking, why would the stations that multicast matter? Chances are if it was sent at anything above say 13 - 15 mbps (depending on what they are multicasting) the affiliate wouldn't send the full feed from FOX anyways. That would be like saying NBC will only send their HD feed out at max 13 mpbs because some affiliates multicast Weather Waste.

Times that I have checked the bit rate during scripted HD programs rarely does it hit 13 mbps. I've seen as low as 10.5 mpbs during House and Bones.

Foxeng,

Hope all is well with ya!

I gotta tell ya...Fox's PQ these days almost reminds me of FOX Widescreen SD. Our Fox station doesn't multicast and watching football games on fox has no bite at all. I was ticked when my Cleveland Indians finally got into the playoffs this fall....the TBS pq and sound was stunning. The Fox coverage was downright like a regional broadcast. I am glad Fox has finally offering a lot of things in HD...but they really need to address production and PQ because it makes a difference. I have a 1080p tv now and it makes a huge difference!

I know...I know... :)



You failed to mention that FOX uses variable bit rate shaping, meaning if the picture doesn't need full bandwidth, it doesn't send full bandwidth, only what is needed at that moment. During NFL action shots, the bandwidth goes close to 16 mbs and when no action or still picture, it will drop to around 10 mbs, which is the picture you show here. No action, steady camera.

And no, I don't expect anymore bandwidth than the 16 max that is used now for the SB because some FOX stations have other networks like CW and MNT as subchannels and they can't just turn them off because it is the SB.

Fox is unique with the splicer system as the network feed is sent directly by the affiliates without re-encoding. The actual bitrate for a given program depends on the multiplexing of the multiple streams on the network feed. All the SD and HD feeds for all time zones are sent in a single 73+ Mb/s stream. The stat muxer must be very busy.

Here is what I saw today OTA San Diego (no sub channels).
Looked good at about 16 Mbps.

http://img245.imageshack.us/img245/5972/xetv01wd0.th.jpg (http://img245.imageshack.us/my.php?image=xetv01wd0.jpg)

Here is what I saw today OTA San Diego (no sub channels).
Looked good at about 16 Mbps.

http://img245.imageshack.us/img245/5972/xetv01wd0.th.jpg (http://img245.imageshack.us/my.php?image=xetv01wd0.jpg)

- Silly question, but how do I look at the image in your link? When I click on the imageshack link, it shows a thumnail of the picture that says "920x721 156kb" and not the full size.

When I click on it with firefox, it opens the full size image in a new tab. I can then also view the image at:
http://img245.imageshack.us/img245/5972/xetv01wd0.jpg

When I click on it with firefox, it opens the full size image in a new tab. I can then also view the image at:
http://img245.imageshack.us/img245/5972/xetv01wd0.jpg

- I'm using IE7, which is probably the problem. :)

I can see your second link.

Fox is unique with the splicer system as the network feed is sent directly by the affiliates without re-encoding. The actual bitrate for a given program depends on the multiplexing of the multiple streams on the network feed. All the SD and HD feeds for all time zones are sent in a single 73+ Mb/s stream. The stat muxer must be very busy.
What do they use their other 3 73Mbit/s transponders for? I know the MNTV feed is on one of them, but that's a hell of a lot of wasted space for all but a few hours on Sunday when there are a bunch of different football games on.

For the newbies.

Unlike the other networks that send 45 mbs and the stations decompress and then recompress to < 19 mbs, FOX sends out what is call "ATSC Compliant" signal meaning the signal can be directly taken from the receiver and sent directly to the transmitter, something the other networks can't do. Since OTA has a max of 19.39 mbs, that is the limiting factor for the FOX signal. There is a device called the splicer that literally removes certain bits (coming from the station stream) and inserts or "splices" the network signal into the station stream. Because there is no external manipulation of the network signal such as decompressing and recompressing at the local level, the signal has to be consumer receiver ready straight from the network IRD. FOX uses VBR to improve the signal for stat muxing for those stations who do mulitple streams while not imparing the signal from non multiple stream stations. Any issues you may be seeing isn't due to the local station, but at the network level and everyone sees them, not just a certain station. That is how it works.

So it makes no sense to increase the bandwidth 2 mbs since there is really nothing gained in the long run.

. Unfortunately this causes the PQ to suffer for EVERYBODY, even if your local affiliate does not multicast. .

You would be incorrect as FOX eng points out. FOX also uses high-efficiency encoders, so a lower bit rate is possible. I've seen rates of almost 17 mb/s for nascar, which is more than enough for 720p.

I've never really had a problem with the quality of FOX's HD as far as sufficient bit rates go, so I don't really see a reason for them to raise it much for the Super Bowl. I do wonder at times about the quality of their HD cameras though as fuzz and a general lack of detail are often evident in their shots. Their on screen displays (score bar, etc.) also look pretty bad compared to what NBC and CBS do.

Fox needs to streamline that score bar and make it a box like everybody else does.

You would be incorrect as FOX eng points out. FOX also uses high-efficiency encoders, so a lower bit rate is possible. I've seen rates of almost 17 mb/s for nascar, which is more than enough for 720p.

They can use high-efficient encoders, but I can't stand how I know 30 seconds before that they are going to a "gamebreak" because the resolution turns to poo. That is if they do it quickly and don't keep delaying because of action in the game.

While Fox has gotten better, it is still below ESPN (and a far cry from CBS/NFL Network/NBC's 1080i, even if NBC over compresses) and that is without considering the awful PQ before and during gamebreaks.

Sorry, just wanted to complain. ;)

They can use high-efficient encoders, but I can't stand how I know 30 seconds before that they are going to a "gamebreak" because the resolution turns to poo. Sorry, just wanted to complain. ;)

Oh, I (and others) wouldn't have expected anything else from some here..;)

It goes to "poo" as you say for gamebreak as the studio material is upconverted..:o

I appreciate the Fox approach. Although they were late to the HD party, they have established a good system with decisions and trade-offs made for defensible reasons. And the PQ I get via Fox OTA kicks the stuffing out of the OTA signals I get from my NBC affiliate. CBS does seem a bit better, but not so much that I would want to bash Fox for it.

I appreciate the Fox approach. Although they were late to the HD party, they have established a good system with decisions and trade-offs made for defensible reasons. And the PQ I get via Fox OTA kicks the stuffing out of the OTA signals I get from my NBC affiliate. CBS does seem a bit better, but not so much that I would want to bash Fox for it.

I'm the exact same, I'll take the Fox HD feed from my local, WSYM, everyday and twice on Sunday over NBC, WILX.

The CBS feed is typically very good, but they don't broadcast 5.1 so that drops them down a spot.

Our ABC affil is decent on the PQ and 5.1, but they are very unreliable and seem to not care about HD or investing in it.

Add to the splicer advantage that 5.1 encoding is inherent. Fox also upconverts all 2 channel stereo to 5.1.

There was at least one station (KXII) that re-encoded the HD splicer stream to allow more bandwidth for subs but I don't know the current status. That station had a primary affiliation with CBS and added Fox HD on a subchannel. In that case the PQ is likely below what Fox stations would normally provide.

A disadvantage of the splicer system is the transition to and from the network feed is limited to a cut, but this is how almost every station of all networks operate at the moment. It also is much more difficult to delay the HD network feed by a station (KTVU has done this), but most stations don't have that ability yet either.

Curious if a switch (hypothetically, not going to happen on cable for a long time) to MPEG4 would make a difference?

I appreciate the Fox approach. Although they were late to the HD party, they have established a good system with decisions and trade-offs made for defensible reasons. And the PQ I get via Fox OTA kicks the stuffing out of the OTA signals I get from my NBC affiliate. CBS does seem a bit better, but not so much that I would want to bash Fox for it.

CBS here puts it to shame. Its sad that Fox chose to destroy its HD at the source by leaving room for a subchannel.

Curious if a switch (hypothetically, not going to happen on cable for a long time) to MPEG4 would make a difference?The splicer stream is ATSC ready which means it needs to be MPEG2.

CBS here puts it to shame. Its sad that Fox chose to destroy its HD at the source by leaving room for a subchannel.1 sub channel is perfectly within acceptable standards for a 720p HD channel.

It also is much more difficult to delay the HD network feed by a station (KTVU has done this), but most stations don't have that ability yet either. Wouldn't it be easier? Less data to record...

I still haven't figured out how they are able to get the station ID bugs on the HD image.

Wouldn't it be easier? Less data to record...

I still haven't figured out how they are able to get the station ID bugs on the HD image.It's Fox's patented pixie dust!:D

Seriously, from what I've been reading the splicer takes care of co-branding bugs, too. Initially many stations went with the default bug which tended to get cut off on many TVs (you're watching "FO"???) but our station replaced it with a better-placed "Fox 28" bug.

Supers over HD have been around for a while even on non-Fox stations; most stations can at least super a top-of-hour legal ID if necessary. The only issue is that most of a station's other supers (i.e.: weather crawls, school cancellations, etc.) come from SD equipment and it's hard to get something to work simultaneously and look good on both a 702 x 480i SD picture and a 1280 x 720p or 1920 x 1080i picture. Right now only one station where I live has a system able to do both (and it's not all that intrusive on the HD side, I might add.)

Supers over HD have been around for a while even on non-Fox stations; most stations can at least super a top-of-hour legal ID if necessary. The only issue is that most of a station's other supers (i.e.: weather crawls, school cancellations, etc.) come from SD equipment and it's hard to get something to work simultaneously and look good on both a 702 x 480i SD picture and a 1280 x 720p or 1920 x 1080i picture. Right now only one station where I live has a system able to do both (and it's not all that intrusive on the HD side, I might add.)


Speaking of superimposing an image on a feed. I was watching an FSN HD college basketball game on CSN Chicago over the weekend and noticed that the FSN logo in the Fox Box was covered by a black, but exactly same shaped CSN logo. The black color was a bit too dark to blend into the box completely, but the shape was perfect.

None of the other FSN logos were covered, but I gotta tip my hat to the CSN folks for being creative with the FSN broadcasts.

Speaking of superimposing an image on a feed. I was watching an FSN HD college basketball game on CSN Chicago over the weekend and noticed that the FSN logo in the Fox Box was covered by a black, but exactly same shaped CSN logo. The black color was a bit too dark to blend into the box completely, but the shape was perfect.

None of the other FSN logos were covered, but I gotta tip my hat to the CSN folks for being creative with the FSN broadcasts.


During the FSN broadcasts that are also on other networks such as one of the CSNs, the Fox Box is put in during the transmission test to allow the other networks to align their bug properly.

Wouldn't it be easier? Less data to record...

I still haven't figured out how they are able to get the station ID bugs on the HD image.

The splicer is able to decode just the part of the image where the bug is to be inserted, super the bug and then re-encode that portion.

AIUI Fox statmux their various HD timezone feeds sent out to their affiliate stations on a single transponder - which is also shared with SD. (Not sure if the SD is statmuxed with the HD, statmuxed only with SD, or CBR)

Obviously Fox have to have a maximum bitrate their splicer feed can reach. The difference between this and the ATSC 8VSB standard OTA rate would allow a maximum data rate to be specified for a local station to insert their subchannel(s)

However as Fox are statmuxing the timezone feeds on their distribution system, and not re-encoding at local stations and instead passing on the timezone feed unaltered (apart from local bug insertion - which is done by selectively decoding and recoding only the MPEG macroblocks related to area the bug occupies?) and not using a constant bit rate for their pre-encoded distribution, when one timezone wins over the other, null packets will make up the slack on the losing timezone?

Unless Fox were to distribute all their timezones at a constant maximum bit rate (which would take more transponder space?) they can't switch off the null packets caused by statmuxing.

Similarly unless they distribute two versions of each timezone (one lower rate for stations who add a sub-channel, and one higher rate for those that don't - which could be politically dodgy - as currently all Fox HD in a timezone is of the same quality, and it would also massively increase distribution costs) they can't avoid the null packets on stations with no subchannel caused by leaving space for a subchannel on the network feed passed straight through by the splicer?

The splicer is able to decode just the part of the image where the bug is to be inserted, super the bug and then re-encode that portion.That is really cool!

1 sub channel is perfectly within acceptable standards for a 720p HD channel.
Yeah, that’s what my eyes have told me. I have always thought that the PQ of Fox’s HD programming was good to outstanding, on a par with ESPN/ABC’s and noticeably better than NBC’s. In my estimation, though, the PQ of CBS’s HD offerings is consistently better than anybody else’s, especially their NFL telecasts.

Wouldn't it be easier? Less data to record...I don't think recording is such a big issue but playing it back may be. One option is to decode the stream and record it on a conventional tape machine or server and then re-encode the playback, but this could significantly degrade the PQ. Another approach is to record and playback the ATSC stream directly and use another splicer (or a DTP) to switch between the Fox splicer and the capture playback. As far as a station in a western time zone using the east feed, Fox controls which stream each station receives via the splicer (aka a BP5100).

I think decided to kill regular packets not null packets for the BCS championship game. It was sent with up to 3 mbps less than NFL games.

Hopefully FOX will decide against this for the SB.

Just to recap my readings of Monday night's BCS game on Fox:

WJW-DT, Cleveland, no subchannels. Averaging about 12.5Mbps for the main HD feed ...

http://img511.imageshack.us/img511/4998/foxbcs2008wjwgr1.th.jpg (http://img511.imageshack.us/my.php?image=foxbcs2008wjwgr1.jpg)

The mux stats below are mostly actual game with one commercial break in the middle. Almost no variation in bandwidth usage.

http://img504.imageshack.us/img504/965/foxbcs2008wjwmuxjs8.th.jpg (http://img504.imageshack.us/my.php?image=foxbcs2008wjwmuxjs8.jpg)

Any camera shot that wasn't a closeup looked pretty bad. The main 20/50/20 yard cams showed lots of artifacts.

Just to recap my readings of Monday night's BCS game on Fox:

WJW-DT, Cleveland, no subchannels. Averaging about 12.5Mbps for the main HD feed ...

http://img511.imageshack.us/img511/4998/foxbcs2008wjwgr1.th.jpg (http://img511.imageshack.us/my.php?image=foxbcs2008wjwgr1.jpg)

The mux stats below are mostly actual game with one commercial break in the middle. Almost no variation in bandwidth usage.

http://img504.imageshack.us/img504/965/foxbcs2008wjwmuxjs8.th.jpg (http://img504.imageshack.us/my.php?image=foxbcs2008wjwmuxjs8.jpg)

Any camera shot that wasn't a closeup looked pretty bad. The main 20/50/20 yard cams showed lots of artifacts.

Same thing here from WXIX in Cincinnati (OTA). I recorded the whole game and the average bit rate for the video stream is right around 12 Mbps. Also agree with your subjective observations.

That is really cool!

It would be cooler if they didn't have color capability for the bug. ;)

I'm going to stick my neck out here, and make a long considered observation. Swimming grass is only a problem with 720p, and I've seen it (sporadically) on all of the 720p networks, including ABC, ESPN, FOX, FOX Sports Net. I saw it to a limited degree the other night, too.

Same thing here from WXIX in Cincinnati (OTA). I recorded the whole game and the average bit rate for the video stream is right around 12 Mbps. Also agree with your subjective observations.
Here in Memphis, http://www.avsforum.com/avs-vb/showthread.php?p=12730076#post12730076

Very unimpressed by PQ since the game started. I think there are a couple of field cams that are pretty good, but overall poor PQ. Seeing a lot of swimming grass as if I was watching via D*, but using OTA. Came upstairs and what I found proved my point.

WHBQ, Memphis, no subs. The beginning was during a commercial, until LSU just went up 31-10 and then another commercial break.

http://img247.imageshack.us/img247/7791/whbq1708zv0.th.jpg (http://img247.imageshack.us/my.php?image=whbq1708zv0.jpg)
Lets hope they fix this for the SB.

I'm not an American Football afficionado I'm afraid - nor am I based in the US so intimately acquainted with East Coast, West Coast and Mountain timezones.

However - are football matches shown live on both coasts when they are shown on a national network?

If that is the case - and Fox are statmuxing the network feeds on the same satellite transponder for distribution, with the same material on both feeds, then you would expect a reasonably constant bit rate at a rate lower than Fox can peak at when the two network feeds are showing different material. (This is assuming they aren't also being statmuxed with other totally different services - and that they don't merge the East and West coast feed somehow by PID mapping - which would be difficult to transition in and out of)

However - are football matches shown live on both coasts when they are shown on a national network?
Yes they are and it's hard on the east coast people who are often watching a game past midnight while we're eating dinner over here.

The only reason I like watching football games on FOX rather than the other major networks is because here locally in SLC (FOX13) I can shut the announcers off by listening to the Spanish audio channel. At least this works on my Fuchicomm OTA tuner and all the game sound recorded by those parabolic mikes sounds awesome...and no announcers!;)

God I hope that they don't ruin my Spanish audio channel for the Superbowl!

I'm going to stick my neck out here, and make a long considered observation. Swimming grass is only a problem with 720p, and I've seen it (sporadically) on all of the 720p networks, including ABC, ESPN, FOX, FOX Sports Net. I saw it to a limited degree the other night, too.Very interesting theory! I think the 'swim rate' is the GOP length and is caused by video noise. When a replay is in freeze mode the swimming stops. It will start when the replay starts even if there isn't any movement in the image. I'll have to watch more 1080i for this effect, but I also don't recall it. It may also have to do with the model of encoder is being used. Both Fox and ABC use Tandberg.

The only reason I like watching football games on FOX rather than the other major networks is because here locally in SLC (FOX13) I can shut the announcers off by listening to the Spanish audio channel. At least this works on my Fuchicomm OTA tuner and all the game sound recorded by those parabolic mikes sounds awesome...and no announcers!;)

God I hope that they don't ruin my Spanish audio channel for the Superbowl!

You're giving up a lot just to kill the announcers. The main audio is DD5.1 @ 448kbps and the Spanish audio is DD1.0 @ 192kbps.

You're giving up a lot just to kill the announcers. The main audio is DD5.1 @ 448kbps and the Spanish audio is DD1.0 @ 192kbps.

100% worth it IMHO just to cease the incessant banter...

Very interesting theory! I think the 'swim rate' is the GOP length and is caused by video noise. When a replay is in freeze mode the swimming stops. It will start when the replay starts even if there isn't any movement in the image. I'll have to watch more 1080i for this effect, but I also don't recall it. It may also have to do with the model of encoder is being used. Both Fox and ABC use Tandberg.

The first time I saw it I thought it was related to the GOP length. It looks like errors accumulate over the length of the GOP and then reset upon the arrival of the next I frame.

100% worth it IMHO just to cease the incessant banter...
If you have a 5.1 setup, just unplug the center channel. No more announcers...

The first time I saw it I thought it was related to the GOP length. It looks like errors accumulate over the length of the GOP and then reset upon the arrival of the next I frame.

Interesting to note Fox's GOP length appears to be 15 frames (or 1/4 sec) on the OTA feed, but when I was watching the DirecTV MPEG4 local feed, there were a couple distant shots of the crowd that had a noticeable "tick" to them every second (i.e., every 60 frames, or 1 second) . Makes me wonder if DirecTV is screwing with the GOP length on the MPEG4 locals, as they've been known to do on the old MPEG2 feeds.

The Fox-32 channel in Chicago is pathetic! I use a 720p projector and the Fox HD games are hard to call HD in my mind! CBS and NBC are outstanding and ABC is much better then FOX but still not near the CBS level of PQ.

If that is the case - and Fox are statmuxing the network feeds on the same satellite transponder for distribution, with the same material on both feeds, then you would expect a reasonably constant bit rate at a rate lower than Fox can peak at when the two network feeds are showing different material. (This is assuming they aren't also being statmuxed with other totally different services - and that they don't merge the East and West coast feed somehow by PID mapping - which would be difficult to transition in and out of)

Fox uses four birds, for a total of 16 SD streams and 16 HD streams (4 SD and HD streams per bird/mux). Of that number, 1/2 (two birds) are backup, i.e., not used to directly feed affiliates. All of the streams are available at the affiliate.

Fox controls which stream is provided as the SD video and which HD stream is used at the splicer. The affiliates have zero control over feed selection.

As for how digital is sent out, Fox uses DVB-S 8PSK, using the 8/9 FEC that gets them a mux paylod of 73.726 Mbps. No matter the type of digital transmission, DVB-S, DVB-S2, DVB-T (not used in the US), DCII or ATSC, the number of bits per second must be constant (no I don't know why). That is the reason for the null packet stream.

Now, I'm going to go out on a limb and expect one of the Fox guys to correct me if my theory is wrong.

ATSC must also have a constant payload. That would mean that stat muxing the satellite feed would not be possible, because each of the ATSC HD streams would be a constant 19.2 Mbps. Same for the SD stream, which is also sent out as ATSC (stations are provided with a box to convert from ATSC). Well, that is physically impossible, since the bird's payload is 73.726 and 8 ATSC streams would be 153.6 Mbps.

So, my theory is that the ATSC streams that Fox sends out are not 100% compliant, in that the bit wasting null packets do not exist. Now the stat mux can do bitrate shaping of the MPEG-2 before being placed in the ATSC stream.

That would mean that the splicer inserts the null packets into the ATSC stream at the station's splicer.

Some have been calling for higher bitrates from Fox. Keep in mind that if Fox were to do that, four HD streams at 17 Mbps would require 68 Mbps of bird bits, leaving 5.726 Mbps for four SD streams. Now obviously all four HD streams wouldn't want 17 Mbps at the same time and the SD streams do not need anywhere near what HD needs. During single football events, it would be possible to have one stream be configured for non subchannel affiliates and another stream configured for those who do. Since ALL affiliates would be getting the same program, the other two HD streams would have Fox bars/tone and be severely bit starved. Only one SD stream would be required as well. Lastly they'd have to have the ability in the database to indicate which stations get which feed. They could just code them as two different programs and do it that way.

Is it going to happen? Probably not. Too much work and I suspect that Fox believes that the current bitrate for HD will be just fine.

Is it going to happen? Probably not. Too much work and I suspect that Fox believes that the current bitrate for HD will be just fine.Regardless of the technical details, you have the bottom line right.

Fox uses four birds, for a total of 16 SD streams and 16 HD streams (4 SD and HD streams per bird/mux). Of that number, 1/2 (two birds) are backup, i.e., not used to directly feed affiliates. All of the streams are available at the affiliate.


Yep - that makes sense and covers them for sun outages which are predictable, as well as bird failures, and if uplink locations are not common also heavy rain causing uplink outages?


Fox controls which stream is provided as the SD video and which HD stream is used at the splicer. The affiliates have zero control over feed selection.


Yep - makes sense.


As for how digital is sent out, Fox uses DVB-S 8PSK, using the 8/9 FEC that gets them a mux paylod of 73.726 Mbps. No matter the type of digital transmission, DVB-S, DVB-S2, DVB-T (not used in the US), DCII or ATSC, the number of bits per second must be constant (no I don't know why).


Think that is because the modulation schemes are based on a fixed symbol rate, and thus after modulation / FEC etc. a fixed bitrate. If you don't have enough to fill this bitrate you pad with null packets, as you can't change the symbol rate dynamically as receivers lock to it?


That is the reason for the null packet stream.


Yep - it is filling in the gaps in the constant bit rate that the delivery medium provides.


Now, I'm going to go out on a limb and expect one of the Fox guys to correct me if my theory is wrong.

ATSC must also have a constant payload.

Yes.

That would mean that stat muxing the satellite feed would not be possible, because each of the ATSC HD streams would be a constant 19.2 Mbps.


Think you've made an assumption that Fox distribute their HD feeds as a full 19.2Mbps feed. I don't believe they do. AIUI they statmux their HD network feeds on the satellite, allowing these to vary in bitrate, but not to peak above a maximum.

The splicer is then fed this varying bit rate distribution feed, and then adds any local sub-channels (which have guaranteed space resulting from the statmuxed network feeds having a limited peak). Any gaps - particularly on those stations without sub-channels, are filled with null packets, but these packets are inserted by the splicer at each local station, and aren't sent with the network feed.

I think you are assuming that Fox send each station a 19.2Mbs ATSC full-stream. My understanding is that Fox send each station a statmuxed network feed capped at a certain level, but which can vary and dip below this, with the local station's statmuxer padding with null packets.

I may be wrong.


Same for the SD stream, which is also sent out as ATSC (stations are provided with a box to convert from ATSC).

Yep - SD could be statmuxed or CBR - but will be MPEG2 SD.

An SD ATSC compliant MPEG2 stream doesn't have to be 19.2Mbs - SD can be carried at much lower than this. The BBC use 10Mbs approx to distribute their SD digital networks using MPEG2 (via fibre) to their regional stations, but this is based on local stations decoding and recoding to approx 4.5Mbs MPEG2 for final broadcast.


Well, that is physically impossible, since the bird's payload is 73.726 and 8 ATSC streams would be 153.6 Mbps.


You are assuming SD and HD network feeds are all CBR and all 19.2Mbs. SD networks whether CBR or statmuxed will be likely to be much less than 19.2 Mbs, and the HD network feeds are likely to be statmuxed with each other (and possibly - though possibly not - the SD feeds) and are all likely to have limited peaks well below the 19.2Mbs max. It wouldn't surprise me if TWO HD feeds were statmuxed into a 25-30Mbs pool, and 4 SD feeds into something around the same.


So, my theory is that the ATSC streams that Fox sends out are not 100% compliant, in that the bit wasting null packets do not exist.


Yep - there is no reason for Fox to distribute at 19.2Mbs constant bitrate - they aren't multiplexing the local channel they are just providing the network bit of it. They can thus statmux - with the local splicer filling with null packets as and when it needs to.


Now the stat mux can do bitrate shaping of the MPEG-2 before being placed in the ATSC stream.


Suspect this is less likely - rate shaping would be more costly, and not needed if Fox leave a guaranteed space for sub channels by limiting their network feeds to an agreed amount (say 4Mbs) less than the 19.2Mbs ATSC 8VSB payload. If Fox guaranteed their network feed wouldn't peak above 15Mbs - then there would be 4Mbs for local stations to add subchannel(s) - and fill the troughs where the Fox network statmuxing dropped it below 15Mbvs with null packets. If the station didn't multicast then it would be filling with far more null packets...


That would mean that the splicer inserts the null packets into the ATSC stream at the station's splicer.


Yep - that is what I believe to be the case. No point in wasting satellite distribution space with null packets when they can be generated locally. Better to use the space to carry SD Network feeds?


Some have been calling for higher bitrates from Fox. Keep in mind that if Fox were to do that, four HD streams at 17 Mbps would require 68 Mbps of bird bits, leaving 5.726 Mbps for four SD streams.


17Mbs CBR network feeds would leave only 2.2Mbs for subchannels - which is a bit tight.

My understanding is that Fox statmux their network feeds - and the splicer fills the troughs with null packets.


Now obviously all four HD streams wouldn't want 17 Mbps at the same time and the SD streams do not need anywhere near what HD needs.


Yep - the HD network feeds will fight for bandwith based on their content. This works when they carry different content and falls apart when they carry the same material - say a football match carried live in all timezones and thus on all network feeds?


During single football events, it would be possible to have one stream be configured for non subchannel affiliates and another stream configured for those who do.


If the network commercials are the same for all timezones then that is possible - though I suspect remapping local splicers between feeds seamlessly at the MPEG2 level is likely to be tricky.

I suspect - in fact I'm pretty sure - most network distribution topologies are based on individual feeds constantly feeding specific stations, not remapping stations dynamically. May be wrong - but the latter sounds quite dangerous and a recipe for nasty switching artefacts.


Since ALL affiliates would be getting the same program, the other two HD streams would have Fox bars/tone and be severely bit starved. Only one SD stream would be required as well. Lastly they'd have to have the ability in the database to indicate which stations get which feed. They could just code them as two different programs and do it that way.


Think this is unlikely - my understanding is that broadcasters feel the network is more safely distributed with permanent station to feed mappings.


Is it going to happen? Probably not. Too much work and I suspect that Fox believes that the current bitrate for HD will be just fine.

Think it is too complex and too difficult to implement cleanly and in a fail safe manner. There may also be time-zone specific ad feeds to worry about?

I think you are assuming that Fox send each station a 19.2Mbs ATSC full-stream. My understanding is that Fox send each station a statmuxed network feed capped at a certain level, but which can vary and dip below this, with the local station's statmuxer padding with null packets.


IIRC, one of the Fox engineers on here said the cap for the network HD feed is 16Mbps, so that should give the locally inserted subchannel a worst-case 3.2Mbps minimum to work with.

and if uplink locations are not common also heavy rain causing uplink outages?

Common uplink site in L.A. area. C-band less prone to rain outages, unlike Ku, which hit NBC real hard one day.
The BBC use 10Mbs approx to distribute their SD digital networks using MPEG2 (via fibre) to their regional stations, but this is based on local stations decoding and recoding to approx 4.5Mbs MPEG2 for final broadcast.

They also do not distribute in ATSC :D Fox is the only network in the states that does, because of their splicer system.

My understanding is that Fox statmux their network feeds - and the splicer fills the troughs with null packets.

In a round-about way, I was saying the same thing. I was throwing a bunch of ideas out there.

Yep - the HD network feeds will fight for bandwith based on their content. This works when they carry different content and falls apart when they carry the same material - say a football match carried live in all timezones and thus on all network feeds?

I suspect that today's game is carried on the separate (normal) timezone feeds.

If the network commercials are the same for all timezones then that is possible - though I suspect remapping local splicers between feeds seamlessly at the MPEG2 level is likely to be tricky.

The splicer cannot be told to change feed input if that input is hot. The input can only be changed if it is not hot, i.e., currently running a local break.

I suspect - in fact I'm pretty sure - most network distribution topologies are based on individual feeds constantly feeding specific stations, not remapping stations dynamically. May be wrong - but the latter sounds quite dangerous and a recipe for nasty switching artefacts.

For M-Sa primetime feeds, Fox uses the separate timesone topology. But, for football Sunday, with the number of games that are carried, the games are placed on one of the HD feeds and the station is told which one to use for their area. One weekend Fox frak'd up and loaded the database wrong and the local Fox affiliate was not provided the correct game. Nothing could be done about it until the game went to a local break, at which time Fox net was able to change to the correct HD input. The station was then able to rejoin net. That is a major drawback to the splicer system: 1) dependency on human entry of the database 2) local affiliates have no control over what they get.

Think this is unlikely - my understanding is that broadcasters feel the network is more safely distributed with permanent station to feed mappings.

For typical primetime distribution you are right. For game day, that falls apart, since in a timezone there may be two games, or more, being distributed. They both do not fit on the same stream :D

With CBS, the affiliates are told which feed to take and if the memo had an error, the affiliate can easily change to the correct one.

They also do not distribute in ATSC :D Fox is the only network in the states that does, because of their splicer system

FOX does not distribute in ATSC. ATSC is an emissions format (via 8VSb modulation) only used for terrestrial broadcasting. FOX distributes via 8PSK on satellite. The program streams are typically less than the 19.4 mb/s ATSC rate, and are "spliced" into the local stations transport streams. While there are null pids in the satellite feed, station Null pids and any additional program streams are added locally to make the 19.4 mb/s ATSC data rate.

C-band less prone to rain outages, unlike Ku, which hit NBC real hard one day.
.

True,but high-order modulations, such as 8PSK at 73 mb/s with 7/8 FEC, are prone to rain fade even on C-Band, especially on smaller reflectors; such as a 4.6m.

FOX does not distribute in ATSC. ATSC is an emissions format (via 8VSb modulation) only used for terrestrial broadcasting. FOX distributes via 8PSK on satellite. The program streams are typically less than the 19.4 mb/s ATSC rate, and are "spliced" into the local stations transport streams. While there are null pids in the satellite feed, station Null pids and any additional program streams are added locally to make the 19.4 mb/s ATSC data rate.

I kinda disagree with you, even though you are a "Fox" engineer.

I will agree that it is not 100% ATSC compliant, it is none-the-less ATSC like, so that it can feed the splicer. Nothing stops someone from sending an ATSC compliant datastream via DVB-S or DVB-S2. PBS used to do that with their HD feed. As far as I know, they don't anymore. In any event, the idea is that a majority of the ATSC structure is supplied to the splicer. What gets inserted is the local PSIP data. When going local, the local PID values need to match so that there isn't a massive frak-up when going local.

Because the streams are mostly ATSC format, that is the reason why a normal DVB-S HD compatible receiver will display nothing out of the component outputs. The data needs to be presented to a computer and a program like TSReader used to extract the contents. It is also why the receiver used for the SD feed has to also feed a separate box so that the video and audio can be used by the affiliate. I forget the model number of the box, but can look it up.

I don't want to go back and re-read all of the splicer documentation, but will if I have to.

Maybe all of this is the wrong use of words for many of the terms, but in the end, the data streams that Fox sends out is NOT the same type of data streams sent out by all of the other networks.

True,but high-order modulations, such as 8PSK at 73 mb/s with 7/8 FEC, are prone to rain fade even on C-Band, especially on smaller reflectors; such as a 4.6m.

I believe the FEC is 8/9, not 7/8.

I agree on the reception, but the original conversation dealt with uplink, not downlink.

For those of here that got the east and midwest Fox feed of Terminator, we didn't get the local affiliate bug.

That is very interesting, even though the program started on time, which means they could have used the normal bug insertion control. Was the database even loaded, in case the show did start on time?

Whatever the reason why not, I sure appreciated the mostly clean copy (still had the screwed up closing credits).

I've finished editing the program, now I'm going to watch it commercial free.

BTW, unless I missed a break, there were only four breaks within the show, not the normal five, making it 46:46 in length. The average program bitrate was 11.73 Mbps.

I kinda disagree with you, even though you are a "Fox" engineer.

Bob's station was one of the test beds. He knows the system as well as the FOX engineers in LA.

I think the Fox network HD stream is SMPTE 310. As mentioned the null packets and local PSIP are added at the station. Bitrates can vary. I remember one House I captured a while back was only around 8 Mbs. The whole show with commercials fit on a standard single sided DVD.

I think the Fox network HD stream is SMPTE 310. As mentioned the null packets and local PSIP are added at the station. Bitrates can vary. I remember one House I captured a while back was only around 8 Mbs. The whole show with commercials fit on a standard single sided DVD.
I've noticed both House and Bones at very low bitrates also.

Bob's station was one of the test beds. He knows the system as well as the FOX engineers in LA.

Which would be another good reason as to why our terminologies are not in sync.

I think the Fox network HD stream is SMPTE 310.

Last time I looked, SMPTE documents cost $$$$. You got a copy I can read?

I remember one House I captured a while back was only around 8 Mbs. The whole show with commercials fit on a standard single sided DVD.

I have a lot of Fox shows that fit on a DVD (HD transport stream). Add commercials and none of them would fit. Tonight's Terminator was just over 11 Mbps. A wee bit more action than House :D

I think the Fox network HD stream is SMPTE 310. As mentioned the null packets and local PSIP are added at the station. . .

It's all ASI..The output of the Unity 5000 #1 is fed ASI into the Splicer A1 input with the local multiplex into A2. It does get converted to 310m on the output (downstream of the local multiplexer and the Nielsen NAVEII) using either Tandberg, Tiernan, or Thales interface processors just before the microwave (or exciter for those co-located). And yes, the nullpackets required are added locally, along with the requisite ATSC tables (STT,VCT,MGT,RRT,EIT,ETT and channel ETT).

FOX does not distribute in ATSC. ATSC is an emissions format (via 8VSb modulation) only used for terrestrial broadcasting. FOX distributes via 8PSK on satellite.Bob,

To be sure I understand, is it correct to say FOX is distributing an ATSC compliant signal to their affiliates? This has always been my impression.

As always, many thanks for your participation at AVS,
Ken

Bob,

To be sure I understand, is it correct to say FOX is distributing an ATSC compliant signal to their affiliates? This has always been my impression.

As always, many thanks for your participation at AVS,
Ken

COMPLIANT is the correct word. It is actually a MPEG2 ASI signal that is up to 16 mbs, inserted into the splicer, sent out as ASI then is converted to SMPTE310 for the ATSC exciter at the transmitter. That is the first place ATSC comes into the picture.

Can someone explain why Fox's Saturday game averaged around 15.5Mbps, but the Sunday game averaged around 11.5Mbps ?

Can someone explain why Fox's Saturday game averaged around 15.5Mbps, but the Sunday game averaged around 11.5Mbps ?

Different trucks?

Can someone explain why Fox's Saturday game averaged around 15.5Mbps, but the Sunday game averaged around 11.5Mbps ?

Snow!

Can someone explain why Fox's Saturday game averaged around 15.5Mbps, but the Sunday game averaged around 11.5Mbps ?

Different backhaul conditions, or you received a regionalized feed that had a different bit rate from other regions due to satellite capacity.
Only FOX knows and probably would not say.


Charles (FOXENG) is also correct in his description of "compliant".

The BBC use 10Mbs approx to distribute their SD digital networks using MPEG2 (via fibre) to their regional stations, but this is based on local stations decoding and recoding to approx 4.5Mbs MPEG2 for final broadcast.

They also do not distribute in ATSC :D Fox is the only network in the states that does, because of their splicer system.

But Fox don't distribute in ATSC either - they distribute an ATSC compliant MPEG2 stream for HD - and presumably also SD MPEG2 streams (which may be but don't have to be ATSC SD compliant)

ATSC is, in some ways, a slightly nebulous term in that it defines the 8VSB modulation scheme used OTA, the 19.2Mbs transport stream carried in 8VSB, and the compliance of the MPEG2 video and AC3 audio streams, PSIP data etc. that are carried in this transport stream and that make up the ATSC OTA standard. Whilst Fox may distribute an ATSC compliant HD MPEG2 video stream via satellite - they aren't distributing an entire ATSC transport stream for the local station to pass on untouched, nor are they using 8VSB modulation...

The BBC use MPEG2 SD over fibre for their SD network feeds which is probably output in ASI format by the fibre gubbins to feed into the decoder - where it is decode to baseband SDI locally to recode to MPEG2 SD for SD broadcast (using DVB-T) or ARCed and coded to PAL composite for analogue (Though there is also a separate 140Mbs uncompressed digital PAL composite network feed for analogue). My comment was that the BBC use 10Mbs for their SD station feeds - and wondering how this compared to Fox's SD MPEG2 feeds sent to stations to generate their ANALOGUE networks. It was merely to discuss the relative data rates.

Fox don't have to use ATSC compliant streams for their SD network distribution - and it wouldn't surprise me if they used CCIR/ITU 601 720x480 rather than the ATSC 704x480 as the resolution carried for the SD nets.

Slightly off topic - but only slightly.

Thanks for the clarification about the network feeds - presumably when stations are switching between two HD incoming HD MPEG2 network feeds to "get the right game" the splicer is fed two HD MPEG2 streams received from satellite and does the switch? (i.e. the splicer doesn't just switch between one single network HD feed and a locally encoded HD feed, but can switch between a number of incoming network HD feeds?)

Does sound like a recipe for mis-switching.

(The UK network Five has a similar-ish set-up for its analogue transmitter distribution, as it distributes to its analogue transmitters by satellite (apart from London which is fibred) directly - not via any local station buildings. There are multiple versions of their network to allow for localised commercials - there is no local programming or local news - but rather than regionalise they can re-group the transmitters dynamically based on what advertisers want to do in a break - so they could do North/South/East/West, England/Scotland/Northern Ireland/Wales or do major cities in one region, rural areas in another etc... There are four versions I believe - split across two satellites to cope with sun outages and uplink / downlink and transponder failure, with the "wrong" regions counting as backup)

Different backhaul conditions, or you received a regionalized feed that had a different bit rate from other regions due to satellite capacity.
Only FOX knows and probably would not say.


A regionalized feed for a nationally televised game ?

I would also think the backhaul with be many many Mbps higher than what we get over-the-air. Aren't backhauls usually like 25Mbps - 45Mbps ? Maybe "backhaul" is incorrect term, I'm referring to what is sent from the stadium to the network control. I've seen other people refer to a "fronthaul" as well.

A regionalized feed for a nationally televised game ?

Yes, different commercial payloads.

Does sound like a recipe for mis-switching

We had an issue last year at 9p where an indavertant command was sent, sending the splicer to another feed. The first few minutes of the 8pm program was repeated. :o

A regionalized feed for a nationally televised game ?



Different commercials (and network promotions?) for East and West coast feeds?


I would also think the backhaul with be many many Mbps higher than what we get over-the-air. Aren't backhauls usually like 25Mbps - 45Mbps ?


They can be higher than 45Mbs AIUI - I've heard of 80Mbs being used and also uncompressed HD-SDI over fibre (around 830Mbs for 1080/50i in 4:2:2). (Think that was used at the World Cup in Germany) The SD backhauls from Torino / Turin to London were uncompressed SD (around 170Mbs for 576/50i in 4:2:2)


Maybe "backhaul" is incorrect term, I'm referring to what is sent from the stadium to the network control. I've seen other people refer to a "fronthaul" as well.

Backhaul is the phrase I've heard used most in the US for getting a signal from a remote location to the network centre, with fronthaul describing the feed from the network centre to the stations.

In the UK we use :

"Contribution" to describe the feed from the remote site to the network.
"Distribution" to describe the feed from the network to the station - i.e. the "network" feed.
"Emission" or "Broadcast" to describe the feed from the transmitter to the viewer at home.

So we have contribution circuits (140Mbs PAL composite uncompressed, 34Mbs component ETSI compressed and 165/270Mbs component uncompressed for SD) and Distribution circuits (140Mbs PAL uncompressed and 10Mbs MPEG2 component compressed for SD)

Different commercials (and network promotions?) for East and West coast feeds?



They can be higher than 45Mbs AIUI - I've heard of 80Mbs being used and also uncompressed HD-SDI over fibre (around 830Mbs for 1080/50i in 4:2:2). (Think that was used at the World Cup in Germany) The SD backhauls from Torino / Turin to London were uncompressed SD (around 170Mbs for 576/50i in 4:2:2)



Backhaul is the phrase I've heard used most in the US for getting a signal from a remote location to the network centre, with fronthaul describing the feed from the network centre to the stations.

In the UK we use :

"Contribution" to describe the feed from the remote site to the network.
"Distribution" to describe the feed from the network to the station - i.e. the "network" feed.
"Emission" or "Broadcast" to describe the feed from the transmitter to the viewer at home.

So we have contribution circuits (140Mbs PAL composite uncompressed, 34Mbs component ETSI compressed and 165/270Mbs component uncompressed for SD) and Distribution circuits (140Mbs PAL uncompressed and 10Mbs MPEG2 component compressed for SD)

Your Contribution is our Backhaul (from remote site to studio)

Distribution (although referred to as such here also at networks) is Fronthaul. Often only hear fronthaul used during live events in which another entity is taking network feed for broadcast. e.g. NBC and CBS took NFL Network's fronthaul a couple of weeks ago to distribute to their affiliates.

Emission/Broadcast is same or OTA Broadcast/Transmission

We also do regionalized/sectional commercials. So, multiple feeds of same program with different commercials by same advertiser or by different advertisers in same slot of the varying feeds. Of course, the obvious other usage is sports programming with different competitors.

We had an issue last year at 9p where an indavertant command was sent, sending the splicer to another feed. The first few minutes of the 8pm program was repeated. :o

And it was natually the finals result show of American Idol that night, FOX's biggest show. That was a fun night!

Different commercials (and network promotions?) for East and West coast feeds?

Tighter than that. Time zone. And during football season, per market.

Does anybody know the answer to this question and whether we can expect NBC stations to turn off their subchannels or should we just call it the Macroblock Bowl.

Does anybody know the answer to this question and whether we can expect NBC stations to turn off their subchannels or should we just call it the Macroblock Bowl.

Why would you post a question about NBC in a year old FOX topic?

Closed, and new topic created.