I've heard the comment in the past saying that OTA offers the best quality in HD as it is not "compressed". Can some of you please expand on this please? Is it completely non-compressed? Does it just use MPEG2 encoding for the security features? Is it actually "compressed" just less than the aggressive Cable/Satellite broadcasts?

Pointing me to articles/prior threads to read would be awesome or some responses with fact would be cool as well.

Thanks all, I appreciate the knowledge as always.

i will say i have seen some compression fly's when watching the football games on OTA...

it was in 1080i though.

from what i have seen so far is that OTA is about as good as it gets as far as the compression goes.

try watching a satellite signal compared to OTA and there is a night an day difference.

the satellite signal has compression regardless of whats going on screen.

the thing about compression is that some stations have it while others dont.

the nascar game on sunday was PERFECT.

It is "compressed" (really encoded, the term "compression" when applied to lossy encoding formats is something of a misnomer) using MPEG-2, but generally the bitstream is transmitted at a higher bit rate than what you get via cable. This is because in an effort to fit more channels on the cable network, rate shaping is often applied to the MPEG-2 bitstream to limit how much bandwidth it can consume on the cable network. However, this can cause loss of detail and macroblocking in high-rate/fast motion scenes when the stream is delivered to you.

This is not always the case with OTA stations though. Sometimes, to fit more than one video/audio broadcast on a single OTA channel (multiplexing, or sometimes termed "multicasting", though that's not *exactly* the right term for it), the same sort of rate shaping is applied to the network HD stream. If your local affiliate is broadcasting a weather channel, or some small network (like MyTV, or the former The Tube Music Network or similar), they may be doing this.

There are no "security features" on OTA broadcasts, including ATSC digital - the broadcast flag was *not* passed into law, so it is not used, no hardware actually recognizes it, etc. However, cable networks are not supposed to be able to flag local digital streams with copy-protection flags (sometimes they do, due to lack of knowledge or because they're being anal - however, the Must-Carry rules do *not* allow this). You should be able to do the exact same things with OTA content captured over cable as via OTA directly.

An OTA signal without sub-channels should be around 19 mbps MPEG-2....the D* and E* MPEG-2 HD channels are around 10-12 mbps. They are also downrezzed from 1920x1080.

The new D* MPEG-4 channels are around 10-12 mpbs supposedly, which is good for MPEG-4. They look as good as OTA ever did to me.

I still see some pretty obvious artifacts at times on my 50" Pio plasma on our FOX OTA channel, which has no subchannels.

thank you Rammitinski

i knew i wasnt the only one seeing artifacts on the fox channel.

Charles Wood's 'Industry View' article, "The Hijacking of HDTV...and what you can do to help stop HD Lite," in the Dec. Widescreen Review, rails against poor PQ. "Badly executed compression has created a new generation of listeners that have no clue as to what real audiophile-quality sound reproduction is all about," he writes, indicating the same has happened with HDTV. The problem, he writes, is too much compression, with broadcasters and other services concerning themselves with images on smaller screens rather than 60"--120" sizes. He stresses that viewers should complain to providers and programmers, also threatening premium source cancellations. -- John

Note: HDTV originates from TV cameras or telecines at about 1.5 billion bits per second, is compressed to ~140--800 million bps (Mbps) on tape, then down to ~45 Mbps for big-dish downlinked nationwide distribution , then down to a maximum of ~17 Mbps (video payload) from program sources; multicasting, reformatting, rate shaping, etc. sometimes halving that.Throughout the chain, lossy compression 'tosses out' higher resolutions.

I still see some pretty obvious artifacts at times on my 50" Pio plasma on our FOX OTA channel, which has no subchannels.

And IMHO you always will see some. Just look at the fact that ATSC HD only has about twice the peak bit rate of DVD (19 vs 10 Mbps) but has four times the number of pixels to deal with. So severe motion, strobes, jump cuts, etc, etc ,etc are always going to have peak rate issues. Even DVDs have issues with peak bit rates in some rare cases.

Essentially, OTA has the potential for being the best because, as you mentioned , they are not "compressing it".

To further add to that, as you know, OTA channels are basically the channels you are receiving local, from local broadcast antennas.

When you get those same channels over cable or satellite, "most," if not all of the time, there are compressed to some degree. The receive the channels just as you do, then they compress it to broadcast it through their system.

This will depend on where you are getting it from. I think satellite is guilty the most of compressing the local channels, followed by cable.

Great discussion! Being a noob, I posted a thread in 2 different forums, both ending up here.....questioning what "SNR" and "Signal Power" means. I not only have extremely high SNR according to the responses (27-33 for 7 channels received), but with no compression, it renders an extremely fine picture. This from an 8 bowtie CM 4228 and preamp, all towers 58 miles away over hill and dale.

Analog locals via satelite are the absolute pits! I'll take OTA anyday!

Charles Wood's 'Industry View' article, "The Hijacking of HDTV...and what you can do to help stop HD Lite," in the Dec. Widescreen Review, rails against poor PQ. "Badly executed compression has created a new generation of listeners that have no clue as to what real audiophile-quality sound reproduction is all about," he writes, indicating the same has happened with HDTV. The problem, he writes, is too much compression, with broadcasters and other services concerning themselves with images on smaller screens rather than 60"--120" sizes. He stresses that viewers should complain to providers and programmers, also threatening premium source cancellations. -- John

Note: HDTV originates from TV cameras or telecines at about 1.5 billion bits per second, is compressed to ~140--800 million bps (Mbps) on tape, then down to ~45 Mbps for big-dish downlinked nationwide distribution , then down to a maximum of ~17 Mbps (video payload) from program sources; multicasting, reformatting, rate shaping, etc. sometimes halving that.Throughout the chain, lossy compression 'tosses out' higher resolutions.


Mr. Mason - Your short description of the video compression cycle should be in the FAQ. It is excellent. As for Mr. Wood's article, he's living in a videophile's dream world. The best advice to videophiles is to drop their HD subscriptions and buy into both the HD-DVD and Blu-Ray platforms. Broadcasters will always go for the broadest audience that is increasingly the hand held market (i.e. Video iPod, mobile video enabled phones). Sadly, we just don't have the market strength to get the providers (cable, satellite) to provide the best video quality. Look at the popularity of the MP3 audio format. :(

Essentially, OTA has the potential for being the best because, as you mentioned , they are not "compressing it".Oh, but they are. John's note points out that HD video starts out at 1.5billion bits/sec so anything less than that is "compressed". OTA video is anywhere from 9Mbps to 18Mbps, depending on how many subchannels that they add.

When you get those same channels over cable or satellite, "most," if not all of the time, there are compressed to some degree. The receive the channels just as you do, then they compress it to broadcast it through their system.In regards to cable, this is a common misconception. In many cases (all in my market) cable is allocating the full 18Mbps per HD channel. In fact, there are lots of stations in the country feeding cable via fiber, rather than OTA, with a full 18Mbps bitstream, while those same stations have subchannels and are limiting their OTA to as low as 9Mbps. So there are cases (2 of them here in Rochester) where the cable signal is less compressed than the OTA.

There is a further footnote: FCC regulations prohibit "material degradation" of local OTA digital stations by cable. These regulations, as far as I know, do not apply to satellite.