[mpeg2-dev] Low-level API example code

[Erik W. <om...@te...>]

Here's an attempt at a piece of user code for a basic mpeg2 player, using
the lowest-level API.

This is gonna look like a gstreamer plugin, and really really rough....:

int more_data(bitstream_t *bs, unsigned char **buf, int *len) {
  mpeg2element *element = bitstream_get_private(bs);
  GstBuffer *buffer = gst_pad_pull(element->dec);

  *buf = GST_BUFFER_DATA(buffer);
  *len = GST_BUFFER_SIZE(buffer);

  // store buffer somewhere for future unref
}

// would probably need a callback to unref the buffer

dec = mpeg2_init();
bs = bitstream_init();
bitstream_set_callback(bs,more_data);
bitstream_set_private(bs,element);
mpeg2_set_bitstream(dec,bs);

mpeg2_parse_sequence(dec,seq);

while(1) {
  mpeg2_parse_picture(dec,&pic);
  while (mpeg2_parse_slice(dec,&slice)) {
    while (mpeg2_parse_macroblock(dec,&mb)) {
      mpeg2_idct(dec,&mb);
      mpeg2_motion_comp(dec,&mb);
      mpeg2_place(dec,&mb,&image);
    }
  }
}


A mainloop for something with hardware motion comp would look like:

while(1) {
  mpeg2_parse_picture(dec,&pic);
  while (mpeg2_parse_slice(dec,&slice)) {
    while (mpeg2_parse_macroblock(dec,&mb)) {
      send_mb_data_to_hardware(&slice,&mb);
    }
  }
}


An alternate use for the low-level API is when recoding to something else,
say MPEG-4.  You'd want to extract the motion-vectors and keep track of
them as hints for motion-search in the mpeg-4 code, or even just steal
them <g>.

For something like mp3, there are things you can do with the subband data
that will save you time, like applying basic equalization.  Given a
low-level API for that (parse, process, synthesize), you can do whatever
funky processing you need to.  Totally impossible without a low-level API,
unless you spend a lot more time later doing the processing the hard way
(i.e. doing full motion-search, or applying an expensive EQ).

      Erik Walthinsen <om...@te...> - System Administrator
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