Re: Read frame by frame mp4 file, need example.

[Антон Шаров]

Thank you for reply, Nicolas!
 
>The question is ambiguous, since MP4 containers can contains multiple streams and metadata. Do you want to read each >video frame of the first video frame ? Do you want these to be coded or decoded ? All this is important, because before >pulling this data into your application (I would suggesting using appsink element), you will have to design the right pipeline.
 
I don’t quite understand your clarification because I’m quite new to this domain. I split rtsp stream into mp4 files via
rtsp ! h264depay ! h264parse ! splitmuxsink  location=… max-time-size=5 seconds .
Given camera with 15 fps and ~5 sec. video I suppose that I need to iterate over 75 frames. So it is unclear to me what you mean by «video frame of the first frame». Keyframe and it’s subframes  or I-frame and sequential p-frames or all GOP’s in a file.  I need to extract  timestamp for each frame and find the most accurate frame for a given timestamp.
My pipe for this is filesrc ! decodebin ! appsink, where I hope to handle new-sample or preroll event for each frame (buffer contents == frame).
 
>Frame stepping is unlikely what you are a looking for.
 
I supposed that it means just manual iteration over frames in video file — step by step. Like loop  with opencv. 
  
>Среда, 26 июля 2023, 22:42 +03:00 от Nicolas Dufresne <nicolas at ndufresne.ca>:
> 
>Hi,
> 
>Le mercredi 26 juillet 2023 à 18:48 +0300, Антон Шаров via gstreamer-devel a écrit :
>>Hi.
>> 
>>Where I can find example of reading mp4 file frame by frame, so it was equivalent to OpenCv code like:
> 
>The question is ambiguous, since MP4 containers can contains multiple streams and metadata. Do you want to read each video frame of the first video frame ? Do you want these to be coded or decoded ? All this is important, because before pulling this data into your application (I would suggesting using appsink element), you will have to design the right pipeline.
> 
>Nicolas
> 
>> 
>>while(cap.isOpened()):
>>  # Capture frame-by-frame
>>   ret, frame = cap.read()
>> 
>>I saw this frame stepping example  https://fossies.org/linux/gstreamer/tests/examples/stepping/framestep1.c
>>and .  I’ve tried to recreate this example on gstreamer-sharp and here is my approach:
>>https://gist.github.com/sharov-am/78949b8866235ca14112818385893152
> 
>Frame stepping is unlikely what you are a looking for.
> 
>> 
>>And of course it doesn’t work. I’ve read this doc ( https://gstreamer.freedesktop.org/documentation/additional/design/framestep.html?gi-language=c#frame-stepping )
>>and got from it that there are two main very important parameters like flush and intermediate and sequnce of events:
>>2 step start and 1 step done. Also I expected that appsink preroll or new-sample event would be raised, but nothing
>>happens.
>> 
>>My expectations are: I raise step event, some machinery happens and eventually I handle appsink preroll or new-sample
>>events with needed frame buffer with actual frame. And it continues till EOS (end of file).
>>So, what I’m doing wrong?
>> 
>>Also, I’ve noticed that my pipe has WARN messages like
>> 
>>WARN                 basesrc gstbasesrc.c:3132:gst_base_src_loop:<filesrc> error: Internal data stream error.
>>WARN                 basesrc gstbasesrc.c:3132:gst_base_src_loop:<filesrc> error: streaming stopped, reason not-linked (-1)
>>but I’m not sure that this is the cause…
>>Thanks in advance.
>> 
>> 
>> 
> 
> 
 
 
--
С Уважением,
Шаров Антон
 
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