[Libav-user] Encoding to MPEG2 buffer sizing

Jonathan Noble jonnobleuk at gmail.com
Wed Sep 25 23:49:49 EEST 2019


In my program I am continuously seeing the following 3 messages:

> [mpeg @ 0x7f33b8004200] buffer underflow st=1 bufi=379 size=1024

> [mpeg2video @ 0x7f33b8215280] reencoding frame due to VBV

> [mpeg2video @ 0x7f33b8215280] rc buffer underflow

I am encoding with a constant bitrate where AVCodecContext's bit_rate =
rc_min_rate = rc_max_rate.

I have tried to change the size of rc_buffer_size but I see the following

> [mpeg2video @ 0x7f33b8215280] Warning vbv_delay will be set to 0xFFFF
(=VBR) as the specified vbv buffer is too large for the given bitrate!

> [mpeg @ 0x7f33b8004200] VBV buffer size not set, using default size of

If you want the mpeg file to be compliant to some specification

Like DVD, VCD or others, make sure you set the correct buffer size

> [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.

How does one correctly configure the buffer for a given bitrate in MPEG2?

Kind regards

Jon Noble
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