[linux-dvb] Re: sync problems in 2.4 branch for FF cards

["C.Y.M." <syphir@syphir.sytes.net>]

> Jeremy Hall wrote:
> > 
> > I have heard reports that a/v sync problems in the FF 
> drivers no longer 
> > exist in the 2.6 dvb-kernel tree, however for me they still 
> exist in the 
> > 2.4 tree.  Is it possible the fixes could be committed to 2.4?
> 
> To my knowledge there were no fixes/changes wrt to a/v sync.
> 
> Johannes
> 
> 

I'm currently using the 2.6 branch for cvs dvb-kernel and have had the A/V
sync issue for a long time.  After some investigation, it appears the A/V
desync starts to really happen on channels with lower signal quality.  So,
is this a problem with the actual recording or a problem with playback.
Well, if you have poor signal quality, there is not much you can do if the
dvb card gets an error in the data stream.  A clue to this problem might be
how some other programs can play back the *.vdr files.  If I use VLC to
transcode vdr's *.vdr files, it appears that it is capable of fixing the
errors in the recording by dropping coefficents.  This is a debug log of VLC
playing back a recording that causes major A/V desync:

[msmpeg4 @ 0x83a48b0]warning, cliping 1 dct coefficents to -127..127
[msmpeg4 @ 0x83a48b0]warning, cliping 1 dct coefficents to -127..127
[msmpeg4 @ 0x83a48b0]warning, cliping 1 dct coefficents to -127..127
[msmpeg4 @ 0x83a48b0]warning, cliping 1 dct coefficents to -127..127
[msmpeg4 @ 0x83a48b0]warning, cliping 1 dct coefficents to -127..127
[msmpeg4 @ 0x83a48b0]warning, cliping 1 dct coefficents to -127..127

But, if I try to playback a VDR recording that does not have any A/V desync
problems with VLC, then I do not get these "[msmpeg4 @ 0x83a48b0]warning,
cliping 1 dct coefficents to -127..127" messages when I attempt to transode
the *.vdr file.

So, if there is nothing we can do about the errors in the recordings due to
poor signal quality, then perhaps the driver needs to be able to handle
those errors by doing something similar.

--C.Y.M.