89 lines
2.7 KiB
Plaintext
89 lines
2.7 KiB
Plaintext
ASF Demuxer Plugin
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==================
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Overview
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--------
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This plugin is a demuxer for Microsoft's ASF Advanced Streaming Format
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or ASF [1]. This demuxer only supports ASF v1.0 since the vast
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majority of existing ASF files use that version. The specification
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has been derived from a third party source [2] without reference to
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the original.
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Design
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------
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The ASF format can carry any combination of audio, video or
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'ASF_Command_Media' streams. For simplicity it is assumed that each
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file can carry up to 16 audio streams and 16 video streams. These are
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implemented as dynamic pads and appear as appropriate once the file
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headers have been parsed.
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(-------------------------)
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! asfdemux !
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! (video/raw0)---
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! (video/raw1)---
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! (video/raw...
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--- src !
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! (audio/raw0)---
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! (audio/raw1)---
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! (audio/raw...
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! !
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(-------------------------)
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Known stream fourccs are:
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Type Tags MIME type
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------------------------------------------
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H263 H263 I263 video/x-h263
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MJPEG MJPG image/jpeg
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MPEG4 DIVX divx DX50 video/mpeg
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XVID xvid mp4s
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MP4S M4S2 m4s2
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0x04000000
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MSMPEG4V1 MPG4 video/mpeg
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MSMPEG4V2 MP42 video/mpeg
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MSMPEG4V3 MP43 DIV3 video/mpeg
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WMV1 WMV1 video/x-wmv, wmvversion = (int) 1
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WMV2 WMV2 video/x-wmv, wmvversion = (int) 2
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WMV3 WMV3 video/x-wmv, wmvversion = (int) 3
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WMA1 WMA1 audio/x-wma, wmaversion = (int) 1
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WMA2 WMA2 audio/x-wma, wmaversion = (int) 2
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audio/x-wma, wmaversion = (int) 3
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These video stream headers is very similar to that used in the AVI
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format as are the audio stream headers. In addition the content types
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are basically the same also so, for compatibility with existing
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plugins the src pads are set up as video/x-msvideo. This enables
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compatibility with the ffmpeg plugin.
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The demuxing process begins with the loop function gst_asf_demux_loop
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and parses the file in a recursive tree as follows:
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gst_asf_demux_loop()
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+-> gst_asf_demux_process_object() <----
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+-> gst_asf_demux_process_stream() \
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|-> gst_asf_demux_process_file() |
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|-> gst_asf_demux_process_header() --+
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|-> gst_asf_demux_process_data()
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+-> gst_asf_demux_process_segment()
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+-> gst_asf_demux_process_chunk()
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Todo
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----
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- Support for ASF v2.0
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- Support for command media streams
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References
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----------
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[1] Microsoft. ASF Specification - Windows Media Technologies.
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http://www.microsoft.com/windows/windowsmedia/format/asfspec.aspx (v01.20.01e, September 2003)
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[2] divx at euro.ru. ASF format version 1.0,
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reconstruction. http://avifile.sourceforge.net/asf-1.0.htm
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