Is CQ (constant quality) a variable bitrate?

[thai_tx]

Hi,
Is the CQ option in TMPGENC a variable bitrate or constant bitrate for SVCD? Is there a program to tell what bitrate of an SVCD mpeg file that it was encoded at?

[BJ_M]

if you set CQ to 100 -- it is in fact basicly just about considered CBR -- though is based on a constant Q (CQ) and the other is based on I/O to video buffer (CBR) ..

be aware that accually in both of the above methods the accual bit rate varies a lot.

use bitrate viewer to get a reading of what the bit rate is -- or even properties of mediaplayer or windvd

bitrate viewer is in tools section

[puertorican138]

Constant Quality can give you the best looking picture out of all the rate control modes in TMPGEnc, even though your going to probably end up with an unpredictable filesize. Constant Quality set at 100 can probably give you about 40 minutes of great quality per disk.



Hope That Helps!!! :P

[sterno]

CQ may give you the best picture (my personal testing has not convinced me), but the main reason I usually avoid it is that more than once I've tried to encode clips with CQ and had the file come out with an average bitrate higher than the maximum I set.

[banjazzer]

That shouldn't really happen, of course, but TMPG is known to not always respect the maximum bitrate for 2-pass VBR. So, I suppose it is no surprise that it does the same for CQ mode!

I suppose the answer is to drop the maximum setting slightly.

[sterno]

Yeah, from what some people on here have said CQ is pretty bad about failing to stay inside the bitrate you set (worse than 2-pass VBR). When I encode short clips where I don't really care about the file size for SVCD I sometimes use CQ at 70%-85% with 1800 max, and it usually gives me files of reasonable size and quality. I just avoid using it on clips that have high-action scenes.

[banjazzer]

Well, it seems reasonably OK at keeping to the average bitrate (2-pass VBR). It just doesn't always keep within the maximum setting. However, why I think CQ may be (theoretically) superior to 2-pass VBR is that it will use the bits necessary only by referencing the source material, rather than by being constrained by an average bitrate set in advance of the encoding. Which may, in certain circumstances, be insufficient.