* craft-video: MPEG-4 Part 2 Simple profile encoder
Adds a clean-room MPEG-4 Visual (ISO/IEC 14496-2) encoder behind the new
`mpeg4` / `mpeg4-encode` features: the stream type Xvid and DivX write,
which craft-media already identifies (CodecId::Mpeg4Video) in MP4, Matroska,
AVI and MXF but which no crate could produce.
- I- and P-VOPs, 4:2:0 8-bit, H.263 quantisation, half-sample motion with a
predictor-seeded diamond search, skipped and intra macroblocks in P-VOPs,
intra refresh within the 132 codings of §7.4.5.
- Constant quantiser or 1-pass average bitrate.
- Headers in band (raw .m4v, AVI) or as extradata / CodecParams (MP4, Matroska).
Tests use ffmpeg/ffprobe as external decoders: every coefficient table entry
and escape mode 1/2 event decodes like the fixed-length escape, and encoded
streams decode without diagnostics, close to the encoder's reconstruction.
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Co-authored-by: alehel <git@ornumhelgaker.no>
