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gstreamer/gst/asfdemux
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Ronald S. Bultje 0ea59b7a7b New typefind system: bytestream is now part of the core all plugins have been modified to use this new typefind syste... 
Original commit message from CVS:
New typefind system:
* bytestream is now part of the core
* all plugins have been modified to use this new typefind system
* asf typefinding added
* mpeg video stream typefiding removed because it's broken
* duplicate typefind entries removed
* extra id3 typefinding added, because we've seen 4 types of files
(riff/wav, flac, vorbis, mp3) with id3 headers and each of these needs
to work. Instead, I've added an id3 element and let it redo typefiding
after the id3 header. this needs a hack because spider only typefinds
once. We can remove this hack once spider supports multiple typefinds.
* with all this, mp3 typefinding is semi-rewritten
* id3 typefinding in flac/vorbis is removed, it's no longer needed
* fixed spider and gst-typefind to use this, too.
* Other general cleanups
2003-10-01 13:14:51 +00:00
..
asfheaders.h ASF muxer, largely based on ffmpeg's one, but well-integrated in GStreamer. Demuxer still needs work. 2003-08-26 19:28:20 +00:00
gstasfdemux.c New typefind system: bytestream is now part of the core all plugins have been modified to use this new typefind syste... 2003-10-01 13:14:51 +00:00
gstasfdemux.h New typefind system: bytestream is now part of the core all plugins have been modified to use this new typefind syste... 2003-10-01 13:14:51 +00:00
gstasfmux.c New typefind system: bytestream is now part of the core all plugins have been modified to use this new typefind syste... 2003-10-01 13:14:51 +00:00
gstasfmux.h ASF muxer, largely based on ffmpeg's one, but well-integrated in GStreamer. Demuxer still needs work. 2003-08-26 19:28:20 +00:00
Makefile.am ASF muxer, largely based on ffmpeg's one, but well-integrated in GStreamer. Demuxer still needs work. 2003-08-26 19:28:20 +00:00
README Describes briefly the design of the ASF demux plugin. 2003-01-23 11:20:20 +00:00

README 

ASF Demuxer Plugin
==================

Overview
--------

This plugin is a demuxer for Microsoft's ASF Advanced Streaming Format
or ASF [1]. This demuxer only supports ASF v1.0 since the vast
majority of existing ASF files use that version. The spcification
has been derived from a third party source [2] without reference to
the original.

Design
------

The ASF format can carry any combination of audio, video or
'ASF_Command_Media' streams. For simplicity it is assumed that each
file can carry up to 16 audio streams and 16 video streams. These are
implemented as dynamic pads and appear as appropriate once the file
headers have been parsed.

    (-------------------------)
    ! asfdemux                !
    !                    (video/raw0)---
    !                    (video/raw1)---
    !                    (video/raw...
  --- src                     !
    !                    (audio/raw0)---
    !                    (audio/raw0)---
    !                    (audio/raw...
    !                         !
    (-------------------------)


Known stream fourccs are:

Type		Tags		MIME type
------------------------------------------
H263		H263 I263	
MJPEG		MJPG		video/jpeg	
MPEG4		DIVX divx DX50	video/mpeg
		XVID xvid mp4s	
		MP4S M4S2 m4s2
		0x04000000
MSMPEG4V1	MPG4		video/mpeg
MSMPEG4V2	MP42		video/mpeg
MSMPEG4V3	MP43 DIV3	video/mpeg
WMV1		WMV1

These video stream headers is very similar to that used in the AVI
format as are the audio stream headers. In addition the content types
are basically the same also so, for compatibility with existing
plugins the src pads are set up as video/avi. This enables
compatibility with the ffmpeg plugin.

The demuxing process begins with the loop function gst_asf_demux_loop
and parses the file in a recursive tree as follows:

	gst_asf_demux_loop()
	+-> gst_asf_demux_process_object()   <----
	    +-> gst_asf_demux_process_stream()    \
	    |-> gst_asf_demux_process_file()      |
	    |-> gst_asf_demux_process_header()  --+
	    |-> gst_asf_demux_process_data()
		+-> gst_asf_demux_process_segment()
		    +-> gst_asf_demux_process_chunk()

Todo
----

- Support for ASF v2.0
- Support for command media streams



References
----------

[1] Microsoft. ASF Specification - Windows Media Technologies. 
http://www.microsoft.com/windows/windowsmedia/WM7/format/asfspec11300e.asp

[2] divx at euro.ru. ASF format version 1.0,
reconstruction. http://avifile.sourceforge.net/asf-1.0.htm