Analyze MPEG2 from DVD to see if 2-pass encoding was used

[motown01]

Is there any way to analyze the MPEG2 stream on a DVD to see if a 2-pass encode was used?

[filmboss80]

As far as I know, you can only detect between CBR (constant bitrate) and VBR (variable bitrate). With CBR, you can rule out 2-pass, but with VBR, the only way to assume 2-pass is if the VIDEO_TS folder is a perfect 4.73 for single-layer dvd or 8.75 for dual layer. If not, it might very well be single-pass.

GSpot would be a good tool for seeing if it's CBR or VBR. (It is free in the Tools section of this site.)

[jman98]

Some encoders such as CCE will happily let you do 1 pass VBR or 3 pass VBR or 4+ pass VBR. I don't think there is any possible way to know for sure how many passes are used.

[AlanHK]

HCEnc does one pass using "constant quality", not "constant bitrate". So it would be VBR in either case.

[manono]

That question is so vague as to be pretty much pointless. Is he trying to tell the difference between 1-pass CBR and 2-pass VBR (easy). Is he trying to tell the difference between 1-pass CQ VBR and 2-pass VBR (fairly easy). Is he trying to tell the difference between 2-pass VBR and more passes (3, 4, 5, etc. - pretty near impossible).

[motown01]

I am trying to tell the difference between 1 and 2 pass VBR.

[guns1inger]

Nope. And FWIW, some encoders do multi-pass CBR encoding as well.

Technically, the video only gets encoded once, regardless of the number of passes. In a two-pass VBR encode, the first pass is an analysis pass, with no actual encoding. It is not until the final pass (be it first or fifth) that any actual encoding happens. So as far as the video is concerned, it is always a single pass VBR encode. Only the encoder itself knows differently.

[manono]

I am trying to tell the difference between 1 and 2 pass VBR.

If it's 1-pass CQ VBR, it's usually fairly easy to tell. If it's that ABR garbage you still should be able to tell.

Open the video in Bitrate Viewer:

https://www.videohelp.com/tools/Bitrate_Viewer

if it's 1-pass CQ, the green Q-Level line is usually pretty horizontal, without much fluctuation. This depends greatly on the encoder and the settings used. If it's ABR, the yellow Bitrate line won't have much fluctuation. In 2 or more pass VBR, the Bitrate line should be all over the place, again, depending on the settings, but still much more up and down fluctuation than the ABR encode. You may need experience at using this app to be able to spot the differences.

Technically, the video only gets encoded once, regardless of the number of passes.

CCE writes a playable MPV in the second and every subsequent pass, no matter how many passes you set up. You can't actually play it while the encoding is going on, but you can open it in DGIndex and see it while the encoding is going on, and you can halt the encoding and then play it. Try it sometime.

[guns1inger]

I stopped using CCE some time ago. The last couple of machines I have built have just has HCEnc put on them. The quality is close enough to CCE (and better in some cases).