[FFmpeg-devel] CBR Bitrate control in MPEG-2 video encoder

Michael Niedermayer michaelni
Wed May 26 21:55:38 CEST 2010

On Wed, May 26, 2010 at 09:54:01PM +0200, Sven Brandau wrote:
> Am 26.05.2010 21:30, schrieb Michael Niedermayer:
>> On Wed, May 26, 2010 at 09:22:18PM +0200, Sven Brandau wrote:
>>> Am 25.05.2010 23:30, schrieb Michael Niedermayer:
>>>> cbr (constant bitrate) does not mean constant framesize
>>>> the bitrate that enters the vbv should be constant
>>> And how are you measure the bitrate? In a very simple way you will take 
>>> the
>>> whole time of the video stream and calculate the bitrate from file size.
>>> The only question is (beside the vbv constrains) how small is the time 
>>> unit
>>> in which the bitrate will be calculated. 1s? 30s? ...?
>> you must read and understand the mpeg specs and how vbv works, this 
>> discussion
>> is pointless otherwise.
> Yes ok.  :-)
> But how calculate the ffmpeg cmd tool the showed bitrate during encoding? I 

wrongly in this sense :)

> guess without the knowledge of the mpeg-2 vbv model?


>>>> and only a true mpeg2 stream analyzer can tell you the bitrate prior to
>>>> the vbv. Your mail does not sound like you used such a tool
>>> You are right, I don't have such a tool. Have you ever tried such a tool 
>>> on
>>> the ffmpeg MPEG-2 video encoder?
>> some people did
> Ok, and how is ensured that the ffmpeg MPEG-2 video encoder fullfills the 
> specs for vbv? Was there a test with a
> true mpeg2 stream analyzer and the result was fine for a set test streams?

iam not aware of any vbv issues and i know some people tested streams from
ffmpeg. Id assume they would have reported it where there issues ...


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

No human being will ever know the Truth, for even if they happen to say it
by chance, they would not even known they had done so. -- Xenophanes
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