[FFmpeg-devel] [BUG] transcode DVD films have a/v sync issue

[Michael Niedermayer]

Hi

On Wed, Sep 12, 2007 at 12:12:58PM +0800, Limin Wang wrote:
> Hi,
> 
> > On Tue, Sep 11, 2007 at 07:19:25PM +0800, Limin Wang wrote:
> > > Hi,
> > > 
> > > I'm try to transcode some dvd to ts(h264) by ffmpeg, if the dvd is DVD films,
> > > the output will lose A/V sync and video can't play smoothly.
> > > 
> > > Below is simple command line to reproduce it:
> > > lmwang at test1-desktop:~/dev/ffmpeg$ ./ffmpeg -i
> > > /home/lmwang/bitstream/24fps.vob -b 1500kb -bf 3 -coder 1 -refs 4 -partitions
> > > all -vcodec libx264 -ab 96kb -ar 48000 -ac 2 -acodec mp2
> > > /mnt/dvd_result/test_1500kb.ts
> > 
> > our mpeg ts muxer is broken, it writes random timesamps (yes i verified that
> > the dts/pts ffmpeg feeds into the muxer are quite different from the totally
> > nonsensical dts/pts that our mpeg ts demuxer returns)
> > use mpeg-ps and -vsync 0 it works, without -vsync 0 your output will be
> > full of duplicated frames, though it works as well if your system is fast
> > enough
> 
> So when we need to enable vsync?  

when you want (or need) average framerate == 1/timebase or to say it
differently when you want or need your video to be strictly constant
framerate like for the case that your container doesnt has timestamps


> what's the purpose of vsync?  

see above


> why vsync is
> enable default, but async is disable default? 

historic reasons (=dont change default if theres no strong reason to ...)


> 
> > 
> > if you want to fix the mpeg ts muxer look at the patches from xiaohui
> > (some on the mailinglist some in the soc svn) and help cleaning them up
> > maybe they fix the timestamps
> 
> OK, I'll try to search these patches to get some basic understanding.

great

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I hate to see young programmers poisoned by the kind of thinking
Ulrich Drepper puts forward since it is simply too narrow -- Roman Shaposhnik
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