Bitrate Question

[EpheMeroN]

I have a video that is 43:37:08 long and I want to encode it to fit onto a DVD-5. The AC3 file is 384kbps.

My question is, won't a CBR bitrate of say 9250 work just as well as using VBR, if not better? With such a high bitrate allowance for this project, I didn't see how using the normal VBR would benefit me at all qualitywise.

[Video Dude]

There is a misconception that the higher the bitrate the better. But in reality you may be wasting bits and causing perfomance issues. A major concern would be if your dvd player could sustain smooth playback (especially at the end of the disc) for that high a cbr bitrate. It would depend on the quality of your dvd player, media, and burner.

If a video frame achieves maximum PQ at say 7000, then using a higher bitrate on that frame would be unnoticeable and thus "wasted".

[EpheMeroN]

Is there any ways to tell where the max pq bitrate is being used so I don't waste bits?

[neo squidward]

What is PQ and how do you view it?

[Video Dude]

PQ is an abbreviation for Picture Quality.


It really depends on the encoder being used.

For instance, TMPGEnc 2.5 has a "Constant Quality" mode in which you can set it to 100%. If you then specify a max bitrate of 9250, it will do a one pass vbr in which it will allocate the maximum number if bits per frame as needed for full quality, but not going over 9250.

CCE SP has a similar feature in the Q Factor setting for one pass vbr (low Q = high quality). I think that the free encoder HC has a similar feature.


I would typically encode a video of that length with a multipass vbr with: min=800, avg=8000, max=9000. But a lot depends on the complexity of the video.

It is always good to experiment. Try the cbr and see if it will work. I have had mixed results with a high cbr, with some players working perfect while other players would stutter every five seconds at the end of the disc.

Since file size is not an issue in this case, you only need to be concerned about wasted bits if it affects playback performance.

[PhillipWyllie]

I wouldn't encode using CBR, use VBR. Using CCE VBR settings editor you can tailor the bitrate so the movie fits nicely on a DVD-5(without any loss in quality). If the length is around 43 minutes you'll have no problem (even at the highest bitrates).