[FFmpeg-devel] [PATCHv2 2/3] avformat/utils: increase detected start_time with skip_samples

[Marton Balint]

On Tue, 8 Mar 2016, Hendrik Leppkes wrote:

> On Tue, Mar 8, 2016 at 10:54 PM, Marton Balint <cus at passwd.hu> wrote:
>>
>> On Tue, 8 Mar 2016, wm4 wrote:
>>
>>> On Tue,  8 Mar 2016 21:29:52 +0100
>>> Marton Balint <cus at passwd.hu> wrote:
>>>
>>>> Signed-off-by: Marton Balint <cus at passwd.hu>
>>>> ---
>>>>  libavformat/utils.c               | 10 ++++--
>>>>  tests/ref/fate/gapless2-ipod-aac1 | 72
>>>> +++++++++++++++++++--------------------
>>>>  tests/ref/fate/gapless2-ipod-aac2 | 72
>>>> +++++++++++++++++++--------------------
>>>>  3 files changed, 80 insertions(+), 74 deletions(-)
>>>>
>>
>>> I'm a probably bit late here, but what's the rationale of increasing the
>>> start time?
>>>
>>
>> According to docs, start time is supposed to be the pts of the first
>> decoded frame, therefore skipped samples must be taken into account, when
>> the start time is determined based on the first packet pts.
>>
>
> But the skipping is performed by avcodec, not avformat, isn't it?

Yes.

> start_time should be the PTS of the first avpacket coming out of
> avformat, never mind what a decoder might do to that later.

Not according to the docs:

"AVStream->start_time: decoding: pts of the first frame of the stream in 
presentation order, in stream time base. Only set this if you are 
absolutely 100% sure that the value you set it to really is the pts of 
the first frame."

If here frame refers to a packet, why the docs is talking about 
presentation order?

Also check the libavformat/mp3dec.c, it does the same kind of start_time 
adjustment based on the skipped samples.

Regards,
Marton