Simple Bitrate question

[AirGibson]

I have the following AVI video:



It says that the data rate for the video is 827 kbps.

I'm going to convert that AVI to DVD and want to maintain the best quality I can without wasting space on the DVD. I would assume that it would be wasteful to use a bitrate of 5000, for example, when converting since the source's bitrate is only 827.

How can I find the lowest bitrate possible for the video where the encoded video will have the same quality as the source? I want to assume a CBR of 827 would give me the same quality as the source, but that sounds too easy.

[bugster]

How can I find the lowest bitrate possible for the video where the encoded video will have the same quality as the source? I want to assume a CBR of 827 would give me the same quality as the source, but that sounds too easy.

There is no direct connection between the bitrate of an avi (xvid in your case) and the bitrate required for an mpeg-2. The best possible quality will be obtained using the highest possible bitrate that will still allow the movie to fit on one DVD. However, finding the lowest bitrate that will provide the same quality can only be done by experimentation. Probably the easiest way is to use Tmpgenc CQ mode, with the quality value set at 75 or so, though there are no guarantees of the final quality. You also have to take into account the fact that resizing will be needed to make it DVD compliant and also that mpeg-2 compresses much less than mpeg-4.

In short there is no easy answer, sorry.

[aamir12345678]

bugster, as far as your TMPGEnc CQ method is concerned, you said that 75 would tell you what Mpeg2 bitrate would maintain quality. What should you set your Min & Max to (of the CQ method) in order to get a good idea as to what kind of a bitrate the Mpeg4 will require to look the same as an Mpeg2?

How did you come to 75 as your quality maintaining setting?

Furthermore, if you have the right codecs for each compression, could you use this one setting (a CQ of 75 using TMPGEnc) for every type of compression?

[lenti_75]

i would compress it at 3500-4000, but you have to experiment it.

[bugster]

bugster, as far as your TMPGEnc CQ method is concerned...

How did you come to 75 as your quality maintaining setting?

Furthermore, if you have the right codecs for each compression, could you use this one setting (a CQ of 75 using TMPGEnc) for every type of compression?

1) 75 is just a starting point for experimentation, based on personal experience.

If CQ 75 provides the quality you want/need, by all means use it whenever you want. However, remember that with TmpGenc's CQ mode, you have no reliable way of determining the final file size. One two hour movie may come out at 3 Gigs and another at 5Gigs, thats whay you have to do some trial and error. (BTW, those figures are plucked out of the air to provide examples and do not represent anything in the real world!)

[aamir12345678]

Ok, I did some tests. I chose a VBR of 9800-9800-9800 (min-avg-max) as the constant image to be compared to and started doing CQ's starting at 60, then going to 65, then to 70, and on till about 86. The CQ 86 seemed to produce results identical to the VBR of 9800. I did not see a difference between the VBR of 9800, looking at the two images frame by frame using VirtualDubMod.

[bugster]

Ok, I did some tests. I chose a VBR of 9800-9800-9800 (min-avg-max) as the constant image to be compared to and started doing CQ's starting at 60, then going to 65, then to 70, and on till about 86. The CQ 86 seemed to produce results identical to the VBR of 9800. I did not see a difference between the VBR of 9800, looking at the two images frame by frame using VirtualDubMod.

The VBR figures you quoted are the same as using CBR at that rate, no point doing multi-pass in that case, just a waste of time.

Unless you have really high quality source (proffessoinal stuff), then in most case anything higher than 6k is likley to be waste of bitrate (exception may be home video from a hand held cam where camera shake just eats up bitrate). Open the CQ encodes in bitrate viewer to see what actual bitrates you ended up with.

Anyway, if you are happy with the final output quality, thats all that really matters.

[aamir12345678]

--As far as the VBR of 9800, I always thought that it would benefit to do a VBR rather than a CBR. Well, anyways, thanks for the info.

--And you are exactly right. I got bitrate requirements of about 4500 kb/s. I was originally doing a CBR of 7400 on these videos. It's a good thing I read this post and did my tests. Now, I can do a VBR of around 5000 and fit more on a disc. Thanks.