GStreamer: how to read mp4 frame by frame and extract capture (camera) time? Need to find closest to given ts frame

Question

Given some timestamp (probably second or ms precision), I need to exctract closest frame in mp4 file with assumed camera timestamp(captured time, not pts or dts) for each frame, what is a more appropriate pipeline to exctract each frame within it's captured timestamp (smth like to use GetReferenceTimestampMeta from buffer)? Given that I work via gstreamer-sharp I expect to use appsink events, smth like:

  private static void AppSink_NewSample(object o, NewSampleArgs args)
    {
       
        if (o is AppSink aps)
        {
            var sample = aps.PullSample();
            var buf = sample.Buffer;
            buf.Map(out var info, MapFlags.Read);
     
            //application/x-rtp
            var tsMeta = buf.GetReferenceTimestampMeta();
            //NOTE tsMeta shouldn't be null there...
            //TODO some timestamps compare logic

            buf.Unmap(info);
        }

        Counter++;
    }

Put it simple -- I need to iterate over frames and select one based on some condition (actually, closest to given timestamp).

Thanks in advance.

Answer 1

I found the way, it is smth like:

            var appSink = (AppSink) readerPipe.GetByName("my_appsink");
            readerPipe.SetName($"frame_stepper");
            var q = readerPipe.SetState(State.Playing);

            var step = 1; 
            while (step < frameNumber)
            {
                appSink.PullSample();
                step++;
            }