splitmuxsink and timestamps

[Jan Schmidt]

Hi,

On 19/04/17 10:21, Philippe De Muyter wrote:
> Hi Jan,
> 
> On Tue, Apr 18, 2017 at 09:05:56PM +1000, Jan Schmidt wrote:
>> Hi,
>>
>> On 18/04/17 19:26, Philippe De Muyter wrote:
>>> Hello Jan and list
>>>
>>> I would like to enhance splitmuxsink's "location" property with a way
>>> to produce files named after the absolute timestamp of the first frame
>>> included in the file.
>>>
>>> Which of GST_BUFFER_PTS, GST_BUFFER_DTS or GST_BUFFER_TIMESTAMP
>>> should I use for that purpose ?
>>>
>>> I work on a arm board running linux equipped with a camera sensor, and
>>> synchronised using ntp.  Myv4l2 driver produces UTC-time timestamps of
>>> each frame.
>>>
>>> Also, is there a container format that can hold those absolute timestamps,
>>> in order to retrieve them when replaying the file ?
>>
>> In GStreamer 1.12 (and in the 1.11.90 pre-release), there's a
>> format-location-full signal on splitmuxsink that lets you do what you
>> want. It passes the first buffer of a new fragment, and you can use
>> whichever timestamp you want for generating the output filename.
> 
> Thanks
> 
> Is that useable by a gst-launch pipeline ?

No, you need some code to connect to the signal and calculate the
filenames. A python script should do it.

>> GST_BUFFER_TIMESTAMP is an alias for GST_BUFFER_PTS, so they're the same
>> time.
>>
> Is it meant to contain the absolute capture timestamp of the frame ?
> Or is another timestamp field available for that purpose ?

Short answer: No.
Longer answer: PTS can contain whatever timestamp upstream decides -
it's just an incrementing time with some arbitrary start point that
increases according to the playback/capture rate of the video according
to the clock it's being measured against..

> And when replaying h264 encoded files produced by splitmuxsink using splitmuxsrc,
> is it possible to retrieve the original capture timestamps of the frames ?

You'll need to use timecodes for that. Hopefully someone else can
answer, because I've never used them.

- Jan.

> 
> Philippe
> 

-- 
Jan Schmidt, Centricular Ltd - http://centricular.com/

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