[Ffmpeg-devel] [BUG] Error: 2pass curve failed to converge

[Rich Felker]

On Tue, Jul 18, 2006 at 02:18:31PM -0700, Loren Merritt wrote:
> On Mon, 17 Jul 2006, Corey Hickey wrote:
> 
> >This bug is a bit elusive; it only happens with some source videos with
> >some parameters, and is not always the same between amd64 and i386. In
> >each case, the second pass fails immediately with the error:
> >
> >[mpeg4 @ 0xc840d0]Error: 2pass curve failed to converge
> 
> The bug turns out to be unrelated to my earlier suggestion.
> Uncomment the printf at ratecontrol.c:908 to see what's going on:
> 
> predicted_size target_size rate_factor
> 23365008.042328 24398207 65536.000000
> 23365008.042328 24398207 98304.000000
> 23365008.042328 24398207 114688.000000
> ...
> 
> So the error message is triggering as intended. It's telling you that it 
> can't spend that many bits subject to lmin=2.
> 
> But pass1 ended up being vqscale=2 at 828 kbit/s, while you're only asking 
> for 817 kbit/s on pass2, and the predicted size for pass2 at vqscale=2 is 
> 782 kbit/s. So the bug is that even if the 2nd pass's quantizer is the 
> same as the 1st pass, it does not predict the size to be exactly what was 
> observed in the 1st pass.

moreover this bad prediction could explain many users' complaints that
lavc will not utilize all the bitrate they give it..

rich