Problem: probe() and MediaPool's movie sources called std::fs::read and then
filmcraft_codecs::open_bytes, so a clip cost its full size in memory, twice
while probing (a 245 MiB MP4 peaked at 494 MiB just to import).
Fix: container footage on disk is opened through a positional-read
ByteReader (stream::FileReader) and FilmCraft's reader openers
(filmcraft_media::reader::open_reader; MP4/MOV, Matroska/WebM, MXF, Ogg,
MPEG-PS/TS), which read the index and then single samples. Probing takes this
path only when nothing probed before containers (still/model extensions,
PSD/SVG/PDF, image magic) claims the file; everything else, whole-file audio
formats, in-memory files (add_bytes) and wasm32 builds keep the byte path.
Regression test: probing and decoding a frame and audio of a movie with a
256 MiB tail grows peak RSS by <64 MiB (512 MiB before), same results.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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