Impossible to get the right file size after encoding

[cd090580]

Hi,

I have several small clips (from avisynth) that I want to encode to DVD.

For these clips I have about 3,21 GB free to fit them on a DVD.
The duration is 43 minutes 44 secondes.

The bitrate I found is about 4700 kbps and 256 kbps for audio.

I encode them with CCE SP with the following settings:

Average bitrate: 4750 kbps
Mininum: 4000 kbps
Maximum: 9500 kbps

Audio: Wav (Will be converted to AC3 during authoring process with Tmpgenc DVD Author)

After encoding all files, I end up with only 1,92 GB (both video and audio in wav format).

What's wrong in my encoding settings ?????

[jagabo]

This isn't about your problem but... there's not much point in using a minimum bitrate setting that's so close to the average. In order to allow higher bitrates when needed the encoder has to use a lower bitrate on other scenes. The two have to balance out in order to maintain the average bitrate. Using a minimum of 4000 kbps is a waste since many scenes will not require that much (a 1 second black pause between scenes, still shots, etc.).

Regarding you undersized files: I don't think they are undersized. 4750 kbps for ~44 minutes should give about 2 GB with LPCM audio.

[cd090580]

Ok, I've entered wrong duration when I first calculated my bitrate.

For 45 minutes, the videohelp bitrate calculator indicate to put 9537 kbps for video (audio will be 256 kbps ac3).

So, what's the best values I need to enter in cce to achieve the wanted size while keeping the high quality ?

9500 maxbirate
9000 average
Are these good values ????

but how much for minimum ????

Thanks

[jman98]

I can't recommend those values. Some DVD players are reported to have problems with bit rates that high. Anyway, it's been said that you can't really tell any difference in DVD once the bit rate gets above about 8000 or so. Just use constant bit rate. Variable bit rate is useless with as little video as you have. I'd say use CBR at about 8000 or 8100 and you should be fine. If you feel lucky, you can use 9000, but don't come back complaining if it doesn't work in your player when I warned you that it might not.

Variable bit rate exists to squeeze more quality into a finite space, but you have such a small amount of video (44 minutes is not much) that you don't have a problem with space. If you had 2 hours of video, then yes definitely use VBR. But people have this mistaken belief that VBR is somehow "better" than CBR and that's not true. Encode your video with CBR at 8000 and then encode it with the average bit rate of 8000, the maximum at 9000 and the minimum at 7000 and tell me if you really think the VBR is better than the CBR encoding. When you have less than 1 hour of video, there is no compelling reason not to use CBR.

[cd090580]

Thanks for these recommandations.

Last question, what's the difference between "multipass cbr" and "cbr" ?? I don't see the meaning of using multipass for a constant bitrate ????

[jman98]

There should NOT be an option for "multipass CBR". Multipass only makes sense for VBR encoding. If for some reason you actually can do multipass CBR, don't do it. The encoder should not really be able to use the data from the first pass to make any encoding decisions since it's CBR encoding.

[jagabo]

CBR doesn't mean that every frame gets exactly the same number of bits. In fact, with MPEG encoding it wouldn't make sense to do that since I frames require more bits than P frames and P frames require more bits than B frames. So CBR means that the bitrate averaged over short periods of time will always be the same. (I suspect this is on a per GOP basis.) But within those short periods of time the bits per frame will vary.

The encoder probably doesn't load up all ~15 frames of a GOP, examine them, then spread out the bits as required. It probably works with only a handful of frames at a time (maybe an IBBP, or PBBP sequence). But a GOP might require lots of bits in the first half and not so many in the second half. Since the encoder isn't looking ahead at future frames it might allocate fewer than is really needed in the first half (thinking the entire GOP will be this complex), then allocate more bits than is needed during the second half to achieve the requested average bitrate. A second pass, having a record of the complexity of each frame from the first pass, can more accurately allocate the bits over the GOP.

[manono]

Last question, what's the difference between "multipass cbr" and "cbr" ?? I don't see the meaning of using multipass for a constant bitrate ????

Why ask about things that are explained in the manual? A quick read would have answered that question. Hint: what jagabo said plus it's also for multi-angle DVD creation, something you're not likely to want or need.