[FFmpeg-devel] [PATCH] Make sure AVFormatContext->start_time is initialized after the first patch

[Martin Storsjö]

On Wed, 2 Jun 2010, Baptiste Coudurier wrote:

> On 06/02/2010 12:33 AM, Martin Storsj? wrote:
> > On Fri, 28 May 2010, Martin Storsj? wrote:
> > 
> > > On Fri, 28 May 2010, Baptiste Coudurier wrote:
> > > 
> > > > On 05/25/2010 11:57 AM, Michael Niedermayer wrote:
> > > > > On Tue, May 25, 2010 at 12:54:50AM +0300, Martin Storsj? wrote:
> > > > > > Hi,
> > > > > > 
> > > > > > When discussing a ffserver patch with Baptiste, he insisted that if
> > > > > > AVFormatContext->start_time isn't initialized after the first
> > > > > > packet, it's
> > > > > > a bug that should be fixed within libavformat, instead of handled in
> > > > > > ffserver.
> > > > > > 
> > > > > > This attached patch is one way of solving it, although I'm not sure
> > > > > > if
> > > > > > this is the correct way.
> > > > > 
> > > > > The problem might be that ffserver calls av_seek_frame()
> > > > > with that the first packet demuxed might no longer correspond to the
> > > > > first packet.
> > > > > thus i think its not unreasonable if lavf doesnt set start_time to the
> > > > > first dts/pts once seeking has happened
> > > > 
> > > > Hummm, av_find_stream_info should set the start_time however.
> > > > Isn't av_find_stream_info called ?
> > > 
> > > As far as I can see in open_input_stream, we first call
> > > av_find_stream_info, then a few lines later do av_seek_frame.
> > 
> > Baptiste, ping?
> > 
> > With the current code:
> > 
> >      if (ist->start_time != AV_NOPTS_VALUE)
> >          c->cur_pts -= av_rescale_q(ist->start_time, ist->time_base,
> > AV_TIME_BASE_Q);
> > 
> > Either we assume that start_time shouldn't ever have the value
> > AV_NOPTS_VALUE - in that case we should just remove the if and change it
> > into an assert instead.
> > 
> > If not, if there's even a remote chance that start_time could be
> > AV_NOPTS_VALUE in some cases, this if statement absolutely needs an else
> > branch. If not, the same problem (an absolute timestamp where a relative
> > one was expected) will appear in the rest of ffserver somewhere.
> 
> Then you need to set to set a similar field to ist->start_time in the contact
> and set it to the first pts you get with av_read_frame.

Yes, there is such a field already, c->first_pts.

Would the attached be ok, or should we skip using ist->start_time and only 
use c->first_pts?

// Martin
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