Re: [transcode-users] rc buffer underflow with ffmpeg

[Erik Slagter <erik@xxxxxxxxxxxxx>]

On Wed, 2005-03-02 at 13:49 +0000, Andrew Church wrote:
> >Ah, after reading this, I wonder... perhaps the reason I
> >get tons of buffer underflows when I do 2-pass encoding
> >is because the ntsc_dvd profile uses -w 5000, and whereas
> >that does not ever produce an average bitrate anywhere
> >near that with single pass, maybe it really does with 2-pass,
> >and mucks things up?
> 
>      Actually, the reason is that the current ffmpeg 2-pass rate control
> code is completely broken. :P  IIRC, it completely ignores the max bitrate
> when deciding how many bits to use during the second pass.  There's a patch
> by MeanX somewhere in the FFmpeg list archives that does a better job at
> keeping under the max bitrate in 2-pass mode, but I've found it easier to
> just lower the max bitrate, which seems to affect the first pass enough to
> keep scene peaks under 9800 kbps (my ffmpeg.cfg has vrc_maxrate=7500).

Yep, completely forgotten about that. That's what you get when you
never use 2-pass encoding.

Another simple solution is not to use 2-pass encoding. If you're not
trying to save every single bit, just use 1-pass encoding with a 
slightly higher bitrate or lower "q" setting.