I have looked to see if there is a thread to compare MPEG4 to MPEG2 bitrates but can't find one, so I'll ask here.

I've been recording some stuff off OTA HDTV which is encoded at ~12mbs MPEG2. The output files are often in excess of 10GB TS streams. This obviously poses a problem when I have a collection of 20 of them being >200GB.

Can anyone suggest an approximate bitrate to encode these files in MPEG4 whilst still maintaining the (approximate) source quality? The sources are obviously not bluray quality, (what I am recording has never been released on bluray- my local broadcaster is upscaling with some $$$$$ equipment)

I know that bluray rips to MPEG4 are often 12-14mbs from much higher bitrates, so would 5000-6000kbs be about right (e.g is MPEG2 50% worse than MPEG4, hence half the bitrate would suffice?)

I would be encoding in H.264 using Ripbot264

Many Thanks!

I think the quality achieved by any MPEG4 H264/AVC encoding is significantly dependent on the source material AND the quality of the encoder algorithms.

The more compressed the source, the less efficient subsequent encoding can be (as artefacts already present compromise encoding efficiency), and different H264 encoder algorithms will deliver different quality levels for a given bitrate.

The BBC in the UK have just replaced their broadcast H264 encoders and dropped their bitrate from 16.5Mbs to 9Mbs. If anything, interlaced native content now looks better, though progressive sourced stuff does look a bit softer. However a near halving of bitrate has NOT delivered horrendous picture quality, as the new encoders were massively better.

I think that trial and error - to see what you are happy with - is probably the best route. You may also find that interlaced native and progressive native stuff behaves differently through your encoder - and if you are encoding 24p sourced stuff then a 3:2 removal to extract and encode just the 24p source frames may also help.

The BBC in the UK have just replaced their broadcast H264 encoders and dropped their bitrate from 16.5Mbs to 9Mbs. If anything, interlaced native content now looks better, though progressive sourced stuff does look a bit softer. However a near halving of bitrate has NOT delivered horrendous picture quality, as the new encoders were massively better.

Aren't nearly all UK TV sites complaining about the poor picture quality of BBC HD now it's only 9.7 mbps? They're even making formal complaints to the BBC trust complaining about the poor picture quality and complaining on points of view, and saying the BBC's remit is to "deliver a very high quality technical service to viewers, by adhering to, or seeking to exceed, industry standards for picture resolution" and that it is "visibly failing in that duty". Also, resolution is only 1440x1080 so even that doesn't match or exceed the resolution of other broadcasters, never mind bitrate. And the BBC admitted to problems the new encoders were having with mixes/fades. According to a lot of the UK sites, the BBC is selling off spectrum and not buying spectrum that is available eg. from Channel 4 so that is meaning less bandwidth available for good quality hdtv channels.

Aren't nearly all UK TV sites complaining about the poor picture quality of BBC HD now it's only 9.7 mbps?


Yes - but there is a lot of complaining based on knowing the bitrate has dropped rather than actually looking at the pictures. I've lost count of the number of posters who will not accept that there isn't a simple 1:1 relationship between bitrate and quality.

BBC HD repeats a lot of material - which has resulted in me having the same content recorded before and after the changes. However it isn't a simple 9Mbs = bad, 16.5Mbs = Good.

Yes - the drop in bitrate has caused some changes, just as the change in encoders has. However the drop in bitrate hasn't delivered a near-halving of picture quality. The changes are less marked than you might think reading the OTT comments some people are making.


They're even making formal complaints to the BBC trust complaining about the poor picture quality and complaining on points of view, and saying the BBC's remit is to "deliver a very high quality technical service to viewers, by adhering to, or seeking to exceed, industry standards for picture resolution" and that it is "visibly failing in that duty". Also, resolution is only 1440x1080 so even that doesn't match or exceed the resolution of other broadcasters, never mind bitrate.


BBC HD has always been 1440x1080 - mainly because the two main production formats in use - DVC Pro HD and HD Cam - are 1440x1080 on tape. The BBC is now accepting delivery on HD Cam SR, and some very high end drama is being shot 1920x1080, as is live content, so there is an argument to up the resolution now - but the bulk of current BBC HD content wouldn't benefit from the increase... (DVC Pro HD is the dominant format for factual in the UK)

ITV HD is also 1440x1080 for similar reasons I understand.


And the BBC admitted to problems the new encoders were having with mixes/fades.


Yes - but interlaced native content (sports, entertainment) looks noticably improved with the new encoders - it isn't quite as simple as people are saying. 25p originated stuff does have a softer look though. However nothing looks as bad as the US MPEG2 OTA stuff (even CBS) I've seen - I'm afraid. There is very little visible blocking - if any - apart from on VERY high speed motion (the variable block size H264 uses helps a lot with this).

Of course the new encoders running at 16.5Mbs would be amazing... They'd wipe the floor with every other UK HD broadcast...

However 16.5Mbs was only ever used because the original encoders were less efficient than predicted. I'm surprised that the BBC and Ofcom have decided to drop to 9Mbs already - I'd have thought 12Mbs was more like it currently.



According to a lot of the UK sites, the BBC is selling off spectrum and not buying spectrum that is available eg. from Channel 4 so that is meaning less bandwidth available for good quality hdtv channels.

That's incorrect.

HD broadcasts in the UK will only ever be on the single 40Mbs DVB-T2 mux. The BBC has surrendered this frequency, one of the 6 UK Freeview muxes (and currently one of two the BBC have running at 18Mbs - Mux B). Ofcom - the UK regulator - have allocated the bandwith in this HD mux - the BBC can't buy any more - it isn't for sale... (ITV HD may sublet some of their capacity during the day to 3rd party broadcasters - but C4 are unlikely to)

The BBC have had to switch the SD/Radio services carried on Mux B to Mux 1 (the main BBC Mux) or cease broadcasting them, and will switch BBC Mux 1 to 24-28Mbs DVB-T as digital switch over continues.

Similarly ITV have had to provide a slot for Five (so it is on a primary mux) and shift two of their services to another mux (as there will be three primary public service muxes with near 100% coverage - BBC Mux PSB1, ITV Mux PSB2 and HD Mux B - soon PSB3 - and three secondary commercial muxes with less widespread coverage - and Five is currently on one of these)

To avoid different regions having different services the BBC are going to only broadcast on Mux 1 and Mux B what they will eventually broadcast on Mux 1, and thus prior to changeover there is scope for some leasing of capacity on the soon-to-be-redundant SD Mux B in non DSO regions. To leave this carrying null packets would be a waste of licence-fee payer money.

There is an argument that they should continue with the services they are ceasing in non-DSO regions until DSO - but the BBC have decided to avoid this.

What is confusing many is that Ofcom DID, in their HD planning, suggest that the BBC should be given a slot on Mux 2 (currently ITV/C4 and now Five) - ITV gave up space for Five, and C4 should give up space for the BBC? People are confused as to why this doesn't appear to be happening at the moment.

It wouldn't improve HD bitrates on Freeview HD - that is confined to PSB 3 (currently Mux B) - but it would allow services being ceased (one of the two Press Red interactive video streams for instance) to continue post-DSO.

Yes - but there is a lot of complaining based on knowing the bitrate has dropped rather than actually looking at the pictures. I've lost count of the number of posters who will not accept that there isn't a simple 1:1 relationship between bitrate and quality.

Not only that but also that the new encoders are showing up limitations in the source material that was hidden before -- the best being a complaint by someone about one edition of 'Coast' (a very popular documentary series about the UK coastline and the surrounding area) about how the pictures in the opening shot were very soft and how it was clear proof the bitrate was too low... The shots in question were very obviously upconverted archive PAL material :) Or the classic american neg transfer look of 'Harper's Island' was down to the encoders (obviously, these encoders now do grading :))...

What was really telling (for me at least) about the bitrate changes is that I usually notice a change like this very quickly, and yet I only realised they'd been changed (even though I'd been informed it was about to happen) when someone asked me what I was making of the changed pictures and whether I agreed with the complaints :)

The complainers don't help their cause by pointing to other commercial channels runnign with almost identical compression levels (but higher bitrates, due to being 1920x1080 compared to the BBC 1440x1080) as having better picture quality even though they are riddled with artefacts (just smaller ones :))

BBC HD repeats a lot of material - which has resulted in me having the same content recorded before and after the changes. However it isn't a simple 9Mbs = bad, 16.5Mbs = Good.

I even have some recordings at 18Mb/s ;) BUt I agree, its not black and white in terms of picture quality, and the old encoders were pretty crappy (not much more advanced than MPEG2 encoders as I understand it).

25p originated stuff does have a softer look though.

It depends on the 25p content, some material is looking a little soft but others are fine. I know Andy Quested has talked about introducing a little noise reduction were needed (the old encoders were softening the pictures apparently anyway so it wasn't needed, whilst the new ones don't) so I wonder if we are seeing the effects of that. Certainly, the current series of 'Sarah Jane Adventures' looks very nice. Mind you, I've a feeling that might being shot direct to HDCamSR from Sony F23s (Dr Who currently is and I suspect they are using the same gear).

'Emma' is struggling from what I've seen but that seems to be as much down to the grain from being on film -- I wonder if 2-perf is a bit too grainy for HDTV.

There is very little visible blocking - if any - apart from on VERY high speed motion (the variable block size H264 uses helps a lot with this).

Strictly was struggling tonight in places (which is normally very clean, its shot in the same building as the encoders) particularly the professional's jive, but then that had so much random movement I don't think you could do it justice...

Of course the new encoders running at 16.5Mbs would be amazing... They'd wipe the floor with every other UK HD broadcast...

:) I do wonder whether BBC HD would be better moving to 1920x1080 at 9Mb/s, brickwall filtered above 720cycles per picture width -- i.e. carrying exactly the same resolution as now but with a full raster. This would reduce the size of the artefacts by 25% bringing them in line with Sky1HD etc. It might not work though... Currently, all the artefacts are getting stretched by 33% by the rescaling to 1920.

Steve

Strictly was struggling tonight in places (which is normally very clean, its shot in the same building as the encoders) particularly the professional's jive, but then that had so much random movement I don't think you could do it justice...


Are the encoders at TVC? I thought they were up the road - presentation and playout are...

Are the encoders at TVC? I thought they were up the road - presentation and playout are...

I'm no good at the geography of where the BBC puts things, so I'll bow to your knowledge. I suspect there is a direct uncompressed link from studio to encoder still though.

Steve

I have looked to see if there is a thread to compare MPEG4 to MPEG2 bitrates but can't find one, so I'll ask here.

I've been recording some stuff off OTA HDTV which is encoded at ~12mbs MPEG2. The output files are often in excess of 10GB TS streams. This obviously poses a problem when I have a collection of 20 of them being >200GB.

At 12Mbs the files should be less than 6GB per hour. If they are larger than you may need to strip out the null packets and other unnecessary streams.

I know that bluray rips to MPEG4 are often 12-14mbs from much higher bitrates, so would 5000-6000kbs be about right (e.g is MPEG2 50% worse than MPEG4, hence half the bitrate would suffice?)

I would be encoding in H.264 using Ripbot264

Many Thanks!

Starting with higher bit rates helps with subsequent encodes at lower bit rates. 12Mbs MPEG2 has the potential to already contain a significant amount of artifacts which can reduce the MPEG4 encoding efficiency. The bottom line is how much degradation will you tolerate, so I think some experimentation would be in order. It can also depend on the source material for factors such as the amount of motion, grain, etc. Compression by it's nature is a compromise and while there are objective ways to measure its quality the bottom line is how it looks.

The bottom line is how much degradation will you tolerate, so I think some experimentation would be in order. It can also depend on the source material for factors such as the amount of motion, grain, etc. Compression by it's nature is a compromise and while there are objective ways to measure its quality the bottom line is how it looks.

Will have a play around with my files and see how they turn out.

I may find that I end up not having that much of a problem - I have discovered that some of the programs my TV station has been broadcasting have been severely station-edited (e.g. missing 20 minutes of the program) so there's not much point to them.