> From: Andrew Rowley [mailto:[email protected]] > Sent: 21 June 2010 09:32 > To: 'FFmpeg Users (libav)' > Subject: Video Bitrate settings > > Hi, > > I have been playing about with the video bit rate settings both using the > command line ffmpeg and through the > bit_rate field in the AVCodecContext. > When using the command line, I can change the bit rate, and the file > size > seems to change (although the overall output bit rate seems to be much less > than I specify). When I use > AVCodecContext, the bit_rate seems to be > ignored completely. > >I am using the msmpeg4 codec, although even with the mpeg4, the results are >similar - the bit rate specified >on the command line works, although with >less bits than expected, and the AVCodecContext bit_rate is ignored. > > So my questions are: > >1) Why doesn't the final file bit rate come close to the video bit rate >specified (i.e. out by 1000 at least)? > >2) What do I need to do to make Libav take account of the AVCodecContext >bit_rate parameter (i.e. are there >any flags I need to add)? > >Thanks, > >Andrew :)
To answer my own question 2, you need to make sure that the AVCodecContext time_rate is set to the right value i.e. the correct frame rate for your stream. Otherwise I guess the codec doesn't really know how long each frame is and so can't work out the correct bit rate. Andrew :) _______________________________________________ libav-user mailing list [email protected] https://lists.mplayerhq.hu/mailman/listinfo/libav-user
