[vdr] Re: A/V synchronisation

[Andreas Schultz <aschultz+vdr@warp10.net>]

Hi Joachim,

joachim.koenig@gmx.net wrote:
 > Hi,
 >
 > I do now use vdr (1.0.4) for some time and have the following problem:
 > I use a video beamer as display and an separate amp for the sound.
 > Unfortunately sound and video are always out of sync (the beamer 
delays the
 > picture for
 > app.. 240 ms). I would like to have a function to patch the pts value 
of the
 > sound packets with an offset (configurable). Of course this would 
work only
 > in transfer and playback mode.
 > It would be even better if this offset could be set in the firmware, 
but I
 > assume that the
 > current firmware does not support this. Also I assume that there may be
 > limitations for the
 > offset as the sound needs to be buffered if it is done in the firmware.
 >
 > Don't get me wrong, I do not ask for an implementation (I can do that by
 > myself),
 > but I would like to discuss the issue a bit before doing so. So is there
 > anybody out that may
 > have an opinion an that.

I'm not sure that this would work. The DVB card has only very limited
audio and video buffers. Adding an addional 240ms delay to audio packets
that are already aprox. 380ms late would most certainly overflow those
buffers.
It could be done using a soundcard. Then you are able to delay audio as
much as you like. However the new problem then will be keeping the delay
constant and audio/video in sync.

What you are describing will hit us anyway once somebody creates a
framebuffer device plugin and/or with AC3 playback through soundcards.

The only plugin that deals with manual a/v syncing is currently the dxr3
plugin. The syncing code in there is not from me, but i believe that it
could be modified to introduce almost any audio/video delay.

Andreas




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