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Technical notes:
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Video:
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- The decision intra/predicted macroblock is the algorithm suggested
by the mpeg 1 specification.
- only Huffman based H263 is supported, mainly because of patent
issues.
- MPEG4 is supported, as an extension of the H263 encoder. MPEG4 DC
prediction is used, but not AC prediction. Specific VLC are used for
intra pictures. The output format is compatible with Open DIVX
version 47.
- MJPEG is supported, but in the current version the huffman tables
are not optimized. It could be interesting to add this feature for
the flash format.
- To increase speed, only motion vectors (0,0) are tested for real
time compression. NEW: now motion compensation is done with several
methods : none, full, log, and phods. The code is mmx/sse optimized.
- In high quality mode, full search is used for motion
vectors. Currently, only fcode = 1 is used for both H263/MPEG1. Half
pel vectors are used.
Audio:
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- The mpeg audio layer 2 compatible encoder was rewritten from
scratch. It is one of the simplest encoder you can imagine (800
lines of C code !). It is also one of the fastest because of its
simplicity. There are still some problems of overflow. A minimal
psycho acoustic model could be added. Currently, stereo is
supported, but not joint stereo.
- The AC3 audio encoder was rewritten from scratch. It is fairly
naive, but the result are quiet interesting at 64 kbit/s. It
includes extensions for low sampling rates used in some Internet
formats. Differential and coupled stereo is not handled. Stereo
channels are simply handled as two mono channels.
- The mpeg audio layer 3 decoder was rewritten from scratch. It uses
only integers and can be 16 bit precision for the synthesis filter
at the expense of a slight precision loss. A slower bit exact mode
is available too for compliance testing.
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