[Libav-user] Encoding to MPEG2 buffer sizing

Jonathan Noble jonnobleuk at gmail.com
Fri Oct 4 20:26:56 EEST 2019

I have had a playaround with ffmpeg to get an understanding of what
rc_buffer_size needs to be set to but that didn't provide much information.
Instead I stepped through ffmpeg and I can see that there are 2 buffers
that need to be set up. 1 is in AVCodecContext, the other is in AVStream,

Setting AVCodecContext->rc_buffer_size seems to have to be done in units of
KB. If i use bits as the unit I see this

> [mpeg2video @ 0x7f3a2c805600] Warning vbv_delay will be set to 0xFFFF
(=VBR) as the specified vbv buffer is too large for the given bitrate!

As for setting the buffer in AVStream, I cannot see how it is done.
mpegenc.c gets the buffer_size in a struct AVCPBProperties using a call to

How does one set the values in AVCPBProperties in the AVStream?

On Wed, 25 Sep 2019 at 22:20, Carl Eugen Hoyos <ceffmpeg at gmail.com> wrote:

> Am Mi., 25. Sept. 2019 um 22:57 Uhr schrieb Jonathan Noble
> <jonnobleuk at gmail.com>:
> > [mpeg @ 0x7f33b8004200] ac3 in MPEG-1 system streams is not widely
> supported,
> > consider using the vob or the dvd muxer to force a MPEG-2 program stream.
> Note that independently of your question (I suggest to test with the
> cli), the output
> file will be unplayable with most players as ac3 in mpeg-1 system streams
> are
> typically unsupported (as written above).
> Carl Eugen
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