[M4IF Technotes] ´ð¸´: [M4IF Technotes] Decoder specific in fo for visual atoms

[Dave Singer]

The size problem is an artifact of mpeg4 file format version 1.  We 
thought (wrongly) that we shouldn't pujt a size in the track header 
and sample description, and reserved those fields to 320x240. 
Version 2 fixes that bug.  Most players are 'version 2';  a few 
version 1 players will notice this and check the visual headers for 
the truth.
>-----????-----
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>[mailto:technotes-admin   lists.m4if.org] ?? Stage NexVision
>????: 2003?5?7? 16:18
>???: technotes   lists.m4if.org
>??: [M4IF Technotes] Decoder specific info for visual atoms
>
>Dear experts,
>
>   I'm trying to encode my own MP4 file.
>In order to do this, I've made an MP4 file analyser (atom + descriptor
>analysers)
>Then, I've found a file called "sorenson.mp4" which is very basic and
>plays
>well in all player I have (wmp4player from MPEG4IP project, Philips one,
>TVM4 one, and MPEGable)
>I have extracted the information (ie headers from that file which is
>320x240), and modified them accordingly to my analyser.
>However, on some players, the image is struck to 320x240 size, while in
>some
>it's the right size which is read (720x576).
>
>This is the place in the file where I modified the size values:
>in the tkhd atom, mp4v atom, esds for the scene description atom, and in
>the
>visual bitstream header (directly in the frames)
>
>I've understood all the atom information except in 2 places :
>
>   I am missing some information about 2 little parts of the MPEG4
>standard.
>I've read the ISO 14496-1:1998 document, but I can't find any
>information
>about the decoder specific info for my 'mp4v' atom (descriptor with tag
>0x05)
>I've found the good "decoder specific information" for the 'mp4s' scene
>description, (in chapter 9.3-4).
>In this document, however, for visual track only, they refers to the
>"Annex
>L", I don't have, or I can't find.
>
>Does any of you can explain me if these 'crazy' 32 bytes contains any
>informations about the movie size ?
>
>Decoder specific info
>\/
>05 80808020 00 00 01 B0 01 00 00 01 B5 0E E0 40 40 AF
>00 00 01 00 00 00 01 20 00 84 5D 4C 28 50 20 F0 A3 1F
>
>My second question is where can I find a free BIFS decoder, because I
>can't
>understand easily the first 10 bytes in the "mdat" atom which are BIFS
>commands.
>
>When I try to decompose them, I find some bits that are not described in
>Part 2, (or I don't know where).
>
>I know it's quite a long mail, but if you could arrive till this line,
>you
>might be able to answer me ;-) (please...)
>
>Sincerly
>Cyril Russo
>
>
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-- 
David Singer
Apple Computer/QuickTime