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

Baptiste Coudurier baptiste.coudurier
Wed Jun 2 21:11:30 CEST 2010


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.

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