[MPlayer-dev-eng] RFC [PATCH] mjpa decoder

[Togni Roberto]

Hi all.

Please do not apply this patch: it's a mess and can break other mjpeg 
movies.
The attached patch makes mjpa playable. (samples on ftp, I just 
uploaded a second sample mjpa2.mov).
Some details on mjpa format can be found at 
http://developer.apple.com/techpubs/quicktime/qtdevdocs/QTFF/qtdd-64.html

I had to change output format from YV12 to YUY2, because ffmpeg is 
broken when decoding interlaced files to YV12 format (Y is ok, but 
colors are not).

By the way, also the strandard mjpeg file BABY VOX... on ftp looks 
wrong with YV12 format (look at the orange and blue squares near the 
ligths at the beginning of the movie).

I added some code to force field ordering, because the original ffmpeg 
code don't get it always right: mjpa files have two fields in each 
chunk, top field first, and some other data embedded into JPEG APP1 
marker (mostly needed for type B decoding, only default QT and HT are 
necessary for type A, but my samples don't use them). Please note that 
top field first is just an assumption (got somewhere on the net, now I 
can't find out where), the official way to get frame order is by 
decoding "fiel" section of mov file. Other sections that have to be 
decoded if default tables are used are "mjqt" (quantization tables) and 
"mjht" (huffman tables)

Most of the messy stuff in this patch is needed to access a private 
structure member (bottom_field) of ffmpeg mjpeg decoder.

Now I have to make a choice: should I try to hack mjpa support into 
ffmpeg or write a native Mplayer decoder? If I take this second option, 
should I copy and reuse code from ffmpeg or try to call it? Can I patch 
libavcodec to export what I need (since libavcodec is not part of 
mplayer)?

I'd like to know your opinion about it.

Ciao,
  Roberto
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