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

Baptiste Coudurier baptiste.coudurier
Wed Jun 2 21:36:17 CEST 2010

On 06/02/2010 12:30 PM, Martin Storsj? wrote:
> 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,
>>> 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?

Humm is c->first_pts in ist->time_base ?
I'd like to know also why start_time isn't set in this case :)

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