gst-ffmpeg-0.10.13/ext/ffmpeg/gstffmpegprotocol.c#365

static int
gst_ffmpeg_pipe_read (URLContext * h, unsigned char *buf, int size)
{
  GstFFMpegPipe *ffpipe;
  const guint8 *data;
  guint available;

  ffpipe = (GstFFMpegPipe *) h->priv_data;

  GST_LOG ("requested size %d", size);

  GST_FFMPEG_PIPE_MUTEX_LOCK (ffpipe);

  GST_LOG ("requested size %d", size);

  while ((available = gst_adapter_available (ffpipe->adapter)) < size
      && !ffpipe->eos) {
    GST_DEBUG ("Available:%d, requested:%d", available, size);
    ffpipe->needed = size;
    GST_FFMPEG_PIPE_SIGNAL (ffpipe);
    GST_FFMPEG_PIPE_WAIT (ffpipe);
  }

  size = MIN (available, size);
  if (size) {
    GST_LOG ("Getting %d bytes", size);
    data = gst_adapter_peek (ffpipe->adapter, size);
    memcpy (buf, data, size);
    gst_adapter_flush (ffpipe->adapter, size);
    GST_LOG ("%d bytes left in adapter",
        gst_adapter_available (ffpipe->adapter));
    ffpipe->needed = 0;
  }
  GST_FFMPEG_PIPE_MUTEX_UNLOCK (ffpipe);

  return size;
}