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