[alsa-devel] Audio Video synchronization for data received from a HDMI receiver chip

[Hans Verkuil]

On Wednesday, May 18, 2011 06:10:43 Bhupesh SHARMA wrote:
> Hi,
> 
> (adding alsa mailing list in cc)
> 
> > On Thursday, May 12, 2011 18:59:33 Charlie X. Liu wrote:
> > > Which HDMI receiver chip?
> > 
> > Indeed, that's my question as well :-)
> 
> We use Sil 9135 receiver chip which is provided by Silicon Image.
> Please see details here: http://www.siliconimage.com/products/product.aspx?pid=109
>  
> > Anyway, this question comes up regularly. V4L2 provides timestamps for
> > each
> > frame, so that's no problem. But my understanding is that ALSA does not
> > give
> > you timestamps, so if there are processing delays between audio and
> > video, then
> > you have no way of knowing. The obvious solution is to talk to the ALSA
> > people
> > to see if some sort of timestamping is possible, but nobody has done
> > that.
> 
> I am aware of the time stamping feature provided by V4L2, but I am also
> not sure whether the same feature is supported by ALSA. I have included
> alsa-mailing list also in copy of this mail. Let's see if we can get
> some sort of confirmation on this from them.
>  
> > This is either because everyone that needs it hacks around it instead
> > of trying
> > to really solve it, or because it is never a problem in practice.
> 
> What should be the proper solution according to you to solve this issue.
> Do we require a Audio-Video Bridge kind of utility/mechanism?

I don't believe so. All you need is reliable time stamping for your audio
and video streams. That's enough for userspace to detect AV sync issues.

Regards,

	Hans

> 
> Regards,
> Bhupesh
> 
> > 
> > >
> > > -----Original Message-----
> > > From: linux-media-owner at vger.kernel.org
> > > [mailto:linux-media-owner at vger.kernel.org] On Behalf Of Bhupesh
> > SHARMA
> > > Sent: Wednesday, May 11, 2011 10:49 PM
> > > To: linux-media at vger.kernel.org
> > > Cc: Laurent Pinchart; Guennadi Liakhovetski; Hans Verkuil
> > > Subject: Audio Video synchronization for data received from a HDMI
> > receiver
> > > chip
> > >
> > > Hi Linux media folks,
> > >
> > > We are considering putting an advanced HDMI receiver chip on our SoC,
> > > to allow reception of HDMI audio and video. The chip receives HDMI
> > data
> > > from a host like a set-up box or DVD player. It provides a video data
> > > interface
> > > and SPDIF/I2S audio data interface.
> > >
> > > We plan to support the HDMI video using the V4L2 framework and the
> > HDMI
> > > audio using ALSA framework.
> > >
> > > Now, what seems to be intriguing us is how the audio-video
> > synchronization
> > > will be maintained? Will a separate bridging entity required to
> > ensure the
> > > same
> > > or whether this can be left upon a user space application like
> > mplayer or
> > > gstreamer.
> > >
> > > Also is there a existing interface between the V4L2 and ALSA
> > frameworks and
> > > the same
> > > can be used in our design?
> > >
> > > Regards,
> > > Bhupesh
> > > ST Microelectronics
> > > --
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> > 
> > 
> > --
> > regards
> > Shiraz Hashim
> 
>