mpeg I layer 2 VBR

[Pko]

Does anybody know of a software MP2 encoder that can make VBR, where you could specify the maximum bitrate and it will lower it when possible, mantaining a certain quality level?

I know that toolame is capable of doing VBR MP2s, but the way it does it (or at least the way *I think* it does it) is not useful for what I want to do...

I want to encode a SVCD that is very tight in bitrate (55 min in a 80 min CD, 2 audio streams), so to get better video bitrate, I low the audio bitrates to 112 (very low quality, I know, but bordeline acceptable for my purposes). The thing is, I would like to use VBR to mantain or increase some audio quality and, at the same time, get a higher video bitrate...

I explain:

Let's supose I could make a VBR MP2 with 128 max bitrate but (maintaining some quality parameter) with a lower AVERAGE bitrate... let's say that the average bitrate is around 100 (thanks to some areas of audio silence), and peak bitrate is 128; with that, I will have near 128 CBR quality (better than what I have now) and higher video bitrate (well, the PEAK video bitrate will be lower to compensate for the 256 possible peak bitrate in audio... or I could gamble and take the chance that the video and audio1 and audio2 bitrates will not be all in the same time position...)

TooLame I think that has its VBR function thought to do exactly the opposite; you give it a bitrate it will not go under and it will choose higher bitrates to improve quality... what I want is, maintaining some quality level, decrease the bitrate as much as possible...

(from README.VBR):
"The purpose of VBR is to allow for greatest quality while still keeping a check on the bitrate. "

Well, not in this purpose; a too high peak will cause stutter if the video has a peak at the same time, and I do not really need higher quality (although it will be nice), but lower overall file size of the MP2; that will allow a bigger file size of the m2v and so better video quality.

[Doom9]

VCD, SVCD and even DVD do NOT support any kind of VBR audio...

[Divine]

VCD does not support VBR-AUDIO(mp2).
SVCD does and i 'guess' DVD too.


http://members.tripod.lycos.nl/EdwinVanEck/process/sl00811.pdf

Page6:
'bitrate: may vary from frame to frame'
'The use of VBR is optional on the disc, but the decoder in the player must support this'

So it depends on your HW/SW player, but the official specs by philips allow it.

[Pko]

@Doom9

I was to point you to
http://www.vcdimager.org/pub/vcdimager/manuals/0.7/vcdimager.html#SEC11

(VCDImager documentation, they MAKE the SVCDs so they should know what they speak about), but the link by Divine is even better.

@Divine

Very interesting documentation! thanks...

[ChristianHJW]

Only 3 of 5 DVD players being sold here in Germany will support my self made S-VCDs with VBR video/CBR audio, allthough they fully meet the S-VCDs pecs .... i bet you make your S-VCDs highly incompatible when using VBR audio .... maybe 1 out of 20 players to play them ???

[Pko]

If they do NOT support VBR video (and audio!, but let us take just video for now), the do NOT support properly the SVCD format.

In fact, VBR video is one of the main advantages of SVCD! Not supporting it defeats somehow the purpose of making SVCD, since the alternative will be using low quality video and/or being able to fit very short time in one CD.

And I've made SVCDs with VBR video and they play OK on all the DVD players that are SVCD capable I tried (so far, one or more models from: Shinco, Sampo, Cyberhome, Daewoo). Perhaps the players you tried or the SVCDs that you've made have some kind of problem.

And it is VERY difficult to know if the SVCDs you've made are properly SVCD compliant, for example, all SVCDs made with TMPGEnc versions prior to some recent beta were NOT compliant, although the people that made them thought they were. There are just too many steps and too many different programs.

But what I can tell you is that mine have VBR video and work flawlessly in all players I tried (that have SVCD capability, of course... the problem is that many DVD players DO NOT support SVCD at all, be it CBR or VBR)

[Doom9]

of course all players support VBR video.. after all DVD video is VBR in most cases. But audio is another story. Just a reminder: there are 2 (or was it 3) players that are known to play 5.1ch mpeg2 multichannel audio even though it's part of the SVCD specs. Divide that by the number of all standalone DVD players ever released and you will get an extremely depressive percentage of specs compliant players.

plus.. philips had a standard doc on svcd up on their site but they removed it.. and there I couldn't find anything about vbr audio.

also keep in mind that one reason mpeg2 multichannel was dropped because the VBR audio part didn't work (or so go the rumors.. nobody really knows what were the reasons why mpeg2 mc was dropped from R2 DVDs.. and the ones that were released (a handful) have CBR sound).

[mkanar]

http://members.tripod.lycos.nl/EdwinVanEck/process/sl00811.pdf
^=Published by Philips=^

I believe that Philips previously had the spec at this location: http://www.licensing.philips.com/partner/data/sl00811.pdf

Well, many people are happy to try vbr and test it on their various dvd w/svcd players; perhaps the support is fairly common....

So if tooLame the only and/or best mpeg 1-layer 2 *VBR* encoder? Ah!! It looks like BeSweet support tooLame VBR (experimental MNR). Perfect!

Maybe DVD2SVCD can add this option into DVD2SVCD.

Thanks!
MKanar

[mkanar]

Does SVCD require audio bitrate padding? If not, then it seems as if the player would kind'of have to support VBR audio, intended or not.

[Pko]

Originally posted by Doom9
of course all players support VBR video.. after all DVD video is VBR in most cases. But audio is another story. Just a reminder: there are 2 (or was it 3) players that are known to play 5.1ch mpeg2


*BUT* the specification *DOES NOT* require playing of 5.1ch as such (is allowed to play them as stereo); I quote from sl00811.pdf: "...A MPEG1 decoder will decode the basic sterea (left and right) audio from the multi-channel MPEG-2 audio signal. So it's an option to add a MPEG-2 multi-channel decoder".



multichannel audio even though it's part of the SVCD specs. Divide that by the number of all standalone DVD players ever released and you will get an extremely depressive percentage of specs compliant players.

No, they are all compliant...
And I have some DVD players and all of them play MPEG audio from DVD...


plus.. philips had a standard doc on svcd up on their site but they removed it.. and there I couldn't find anything about vbr audio.


There were many things that where not included in that doc, I think... I've read in more sites (not only vcdimager.org and that previous .pdf) that SVCD specs include VBR audio.

Of course, as we have seen with subtitles, the implementations are mostly very loose, but I think that VBR audio will be played OK (as most SVCD players play 352x480 or 352x576 video, and also most play audio at 48KHz ok... both things in fact go to the MPEG-2 decoder chip, and that chip must process them for DVD, so is only logic that when they receive them from SVCDs will also play OK).

I think that VBR audio will play OK not only because it IS in the spec, but also because the decoder MUST play CBR at 128, CBR at 224, etc. It will not be very smart make a decoder that can play at different bitrates in different streams but is out of specifications because it cannot play different bitrates in the same stream!

Of course, this is just talk, I plan to make some samples and try them in all the machinas I have access.

The thing with the SVCD subtitles is that is a feature many people do not use at all (until now there were only one utility to do them AFAIK!) and not implementing it does not disrupts most of the functionality (you can see the movie, albeit without subtitles). But not playing bitrates other of 224 would almost make the SVCD support nil... And once you have a chip that plays many bitrates, you almost have a VBR audio player... VBR means only that the bitrate can change from frame to frame (of course, each frame alone is CBR!)


also keep in mind that one reason mpeg2 multichannel was dropped because the VBR audio part didn't work (or so go the rumors.. nobody really knows what were the reasons why mpeg2 mc was dropped from R2 DVDs.. and the ones that were released (a handful) have CBR sound).

Well, that where rumours... :-)
I have at least one DVD with MPEG audio (Fargo), and it plays OK; I do not know if it is multichannel or not (my TV is just stereo).

It is not very smart to make audio VBR in a DVD; VBR has only one advantage: you save some space. But in DVD, you have lots of space! even at maximum CBR bitrate (so the same or best quality than VBR), the audio will use an small percentage of the space; the video is what eats most (some DVD do not compress audio at all! they include it in PCM... that is because they have lots of MB available).

But in SVCD, VBR audio makes sense because the space constraint is really strict (is because of that that you see great quality improvements using 80' CDs instead of 74' when you store more than 40' of video)

[Cokes]

guys, think of max. bitrate restrictions versus space on CD.

There isn't MPEG-2 video/audio encoder with some feature as:

"Huh, here I see lot of video action and lot of sound, so I encode say it video at 2404 kbps and audio at 384 kbps. Oh, I here, here is too action, but no audio, so I take say it 2528 video and 192 kbps audio."

Or would you restrict your videostream to max. bitrate at 2404 kbps only for that you have some 384 kbps peaks in audiostream?

Cokes