[MPlayer-dev-eng] A/V sync filter

[D Richard Felker III]

On Tue, Feb 08, 2005 at 02:54:56PM +0000, Tony Houghton wrote:
> In <20050207192239.GM21208 at brightrain.aerifal.cx>, D Richard Felker III wrote:
> 
> > On Mon, Feb 07, 2005 at 11:30:08AM +0100, Diego Biurrun wrote:
> > > Tony Houghton writes:
> > > > I have a problem with loss of A/V sync since I started using the dfbmga
> > > > driver. The picture starts to increasingly lag behind sound, and
> > > > changing the audio delay with the +/- keys has no effect for some
> > > > reason. I think it's caused by using vsync, but vsync is vital for
> > > > watching interlaced TV, and seems to make the picture smoother for
> > > > non-interlaced videos too.  Enabling framedrop drops far too many
> > > > frames. -ao sdl makes a big improvement in the time it takes before the
> > > > gap becomes noticeable but doesn't cure it altogether.
> > > 
> > > Have you already experimented with the -mc and -autosync options?
> > 
> > They won't help. The problem is that video out drivers are not
> > supposed to be synchronous like this in MPlayer's design, but they
> > have to be for playing interlaced video on an interlaced device. It
> > _might_ work ok with -framedrop and -autosync together (better than
> > -framedrop without -autosync) but I'm not sure. The real solution is a
> > decent player design.
> 
> The docs say:
> 
> | Linux sound card drivers have compatibility problems. This is because
> | MPlayer relies on an in-built feature of properly coded sound drivers
> | that enable them to maintain correct audio/video sync. Regrettably, some
> | driver authors don't take the care to code this feature since it is not
> | needed for playing MP3s or sound effects.
> | 
> | [Snip]
> | 
> | Using MPlayer with a properly written audio driver will never result in
> | A/V desyncs related to the audio, except only with very badly created
> | files (check the man page for workarounds). 
> 
> Is that a bit over-simplistic and ignoring the case of using vsync? I
> presume the feature mentioned is something to do with querying the
> card's latency and that even if it is supported, MPlayer's problem is
> that it usually uses it by adjusting the video frame rate, which it
> can't do with vsync?

This has nothing to do with the problem in question here. It can cause
(very!) choppy playback or constant a/v sync mismatch, but never
drifting over time. I thoroughly explained the problem here (with
sync-to-video) already...

Rich