[MEncoder-users] Bug: floating point exception when converting to DV

[Levente Novák]

On Thu, 2007-05-03 at 21:15 -0700, Corey Hickey wrote:
> Levente Novák wrote:
> >> I can reproduce this bug. Sometime in the next day or two, I'll 
> >> investigate it, and there's a change I'll be able to write a patch.
> >>
> >> If anybody else wants to fix it first, though, I wouldn't mind. :)
> > 
> > Thanks in advance! I would fix it myself if I had the necessary
> > knowledge :(
> 
> Here's what I have so far. It's not finished, and it doesn't entirely
> work. I don't really know what I'm doing and some of the patch's hunks
> are probably unacceptable hacks. Finishing the patch and submitting it
> for review (or asking for help) will have to come later; I won't be able
> to proceed until around the middle of next week.
> 
> 

OK, thanks, I will try it as soon as I get home.

> Presently, the visible problem is that lavf's dv muxer discards some
> video frames. This leads to A-V desync and messages like:
> 
> [NULL @ 0xd7a200]Can't process DV frame #9837. Insufficient audio data
> or severe sync problem.
> 
> I don't know how to fix that yet.
> 
> I am encoding with this command:
> $ mencoder /tmp/dv/a.mpg -of lavf -lavfopts \
> i_certify_that_my_video_stream_does_not_use_b_frames:format=dv \
> -oac pcm -ovc lavc -lavcopts vcodec=dvvideo -o /tmp/dv/a.dv \
> -vf scale=720:576 -af resample=48000
> 
> a.mpg is 30000/1001 fps.
> 
> -Corey

What you said is interesting: as Ffmpeg (using the same lavf) does
encode to DV rather well, maybe there are some subtle differences in how
this lavf is used or the switches passed to it. In contrast to MEncoder
where you have to provide these switches yourself, Ffmpeg does it quite
transparently: by setting -target dv a bunch of optimal parameters are
automagically set. BTW how could one dump the lavc/lavf parameters
either Ffmpeg or MEncoder use while perfoming a given action?

I will try your patch with different files/streams/switches during the
weekend, maybe something will be of help.

Thanks a lot again!

Levente