[gstreamer-bugs] [Bug 341977] [asfdemux] wrong framerate/timestamps with geeks.wmv

[GStreamer (bugzilla.gnome.org)]

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  GStreamer | gst-plugins-ugly | Ver: HEAD CVS




------- Comment #3 from Austin Lund  2009-01-12 02:30 UTC -------
The problems seem to be caused by this segment of code in the
gst_asf_demux_process_chunk function:
...
    if (!stream->fps_known) {
      if (!stream->cache) {
        stream->cache = stream->payload;
      } else {
        gdouble fps;
        gint64 diff;
        gint num, denom;

        /* why is all this needed anyway? (tpm) */
        diff = GST_BUFFER_TIMESTAMP (stream->payload) -
            GST_BUFFER_TIMESTAMP (stream->cache);

        fps = (gdouble) GST_SECOND / diff;

        /* artificial cap */
        if (fps >= 50.0) {
          num = 50;
          denom = 1;
        } else if (fps <= 5.0) {
          num = 5;
          denom = 1;
        } else {
          /* crack alert */
          num = (gint) GST_SECOND;
          while (diff > G_MAXINT) {
            num = num >> 1;
            diff = diff >> 1;
          }
          denom = (gint) diff;
        }
        stream->fps_known = TRUE;
        stream->caps = gst_caps_make_writable (stream->caps);
        gst_caps_set_simple (stream->caps,
            "framerate", GST_TYPE_FRACTION, num, denom, NULL);
        GST_DEBUG ("set up stream with fps %d/%d", num, denom);
        gst_pad_use_fixed_caps (stream->pad);
        gst_pad_set_caps (stream->pad, stream->caps);

        ret = gst_asf_demux_push_buffer (demux, stream, stream->cache);
        stream->cache = NULL;

        ret = gst_asf_demux_push_buffer (demux, stream, stream->payload);
        stream->payload = NULL;
      }
...

I have run this through GDB and it seems that the "stream" is optimised out in
my running version.  However the value of "diff" is 279000000.  This would give
a value for "fps" (which is also optimised out) of 3.58 which is < 5 and hence
it sets the frame rate to 5. 

I do not understand the way in which it thinks the FPS should be calculated by
comparing timestamps between buffers.  Does anyone know why things are done
this way?


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