CQ (Constant Quality) setting with tmpgenc

[djnibler]

All, quick question about encoding to MPEG2 for SVCD with tmpgenc: If you set the rate control mode to CQ, and the bitrate to max at 2520, would that not be as high, if not higher quality then any other setting? Would that be the same as doing CBR at 2520? The file sizes would be larger then the VBR modes, but wouldn't quality be as good as VBR, if not better... inlcuding motion etc?

Thanks in advance!

Jeff

[heavyharmonies]

The general consensus (that I've read) seems to go against this, but I don't get it either. I'm having considerably better quality results using CQ than VBR (given roughtly the same resulting file size)...

Then again I'm an utter n00b at this...

[djnibler]

Wierd. I too get better recordings using CQ, then using VBR. I just tested CBR with a maxed bit rate, and it looked better then CQ even. Sigh, this is so confusing!!! I wish there was more documentation out there on this.

Jeff

[kwag]

Wierd. I too get better recordings using CQ, then using VBR. I just tested CBR with a maxed bit rate, and it looked better then CQ even. Sigh, this is so confusing!!! I wish there was more documentation out there on this.

Jeff

There is
http://tangentsoft.net/video/mpeg/enc-modes.html

kwag

[djnibler]

Thanks for the great link Kwag!! Great reading. This confirms what I found in my tests, that CBR ends up being better then VBR more often then not.

That leaves one question: With CBR and tmpgenc, the highest bitrate available is 2520. Would this not mean that even the best CQ converted mpg could not look any better then the same clip converted in CBR at 2520 (the max)? The difference would probably be that the CQ mpg is smaller though... but the quality of the CBR must be the same, if not better correct?

Jeff

[kwag]

Thanks for the great link Kwag!! Great reading. This confirms what I found in my tests, that CBR ends up being better then VBR more often then not.

That leaves one question: With CBR and tmpgenc, the highest bitrate available is 2520. Would this not mean that even the best CQ converted mpg could not look any better then the same clip converted in CBR at 2520 (the max)? The difference would probably be that the CQ mpg is smaller though... but the quality of the CBR must be the same, if not better correct?

Jeff

Yes. But it also depends on the internal algorithms of the encoder used.

For me, CBR is a waste of bandwidht/resources, as it just keeps a constant stream of data without any quantization analysis.

On the other hand, CQ analyzes the frames to try an maintain a quality, and vary the bitrate acordingly.

That's why I am using CQ all the time. And the conclusion of the article above seems to point in the same direction too.

So in theory, if you have your encoder set to CBR 2,520Kbps, it should give you the same quality of CQ=100 at the same bit rate.
But your CQ encoded file size will be lower.

kwag

[djnibler]

Sounds good. All I'm doing for now is recording my favorite half hour show to SVCD. Obviously at 30 minutes, I can go big on the filesize. The encoding time seems similar to me though. If I ever try a whole movie, I'll definately go the CBR route.

With Tempgenc, changing the movement quality checking to highest makes a HUGE difference from what I can tell... though just stepping it down 1 notch cuts the encode time in half.

Thanks again!

[djnibler]

Doh, I meant if I ever do a whole movie, Id use CQ :)

Jeff