| 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 specification |
| 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/raw1)--- |
| ! (audio/raw... |
| ! ! |
| (-------------------------) |
| |
| |
| Known stream fourccs are: |
| |
| Type Tags MIME type |
| ------------------------------------------ |
| H263 H263 I263 video/x-h263 |
| MJPEG MJPG image/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 video/x-wmv, wmvversion = (int) 1 |
| WMV2 WMV2 video/x-wmv, wmvversion = (int) 2 |
| WMV3 WMV3 video/x-wmv, wmvversion = (int) 3 |
| WMA1 WMA1 audio/x-wma, wmaversion = (int) 1 |
| WMA2 WMA2 audio/x-wma, wmaversion = (int) 2 |
| audio/x-wma, wmaversion = (int) 3 |
| |
| 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/x-msvideo. 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/format/asfspec.aspx (v01.20.01e, September 2003) |
| |
| [2] divx at euro.ru. ASF format version 1.0, |
| reconstruction. http://avifile.sourceforge.net/asf-1.0.htm |
