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Implement positioned movie playback opcode

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gamer147
2026-07-29 15:41:01 -04:00
parent 92d7fb295e
commit cfd8809339
18 changed files with 523 additions and 46 deletions
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docs/engine-re.md
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@@ -1705,12 +1705,14 @@ The sole call, `CALLBACK_LOAD@0x189`, clarifies its purpose. Ordinary ADV movie
after `0x236`; the load callback passes that value minus one to `0x241`. This is terminal-frame
reconstruction after a numbered load, not restoration of a separately sampled live playback cursor.
The current FFmpeg backend has no initial-position seam. A faithful implementation should add a synchronous
pre-play seek for both video and audio, discard keyframe preroll until the requested timestamp, then rebase
the existing decoder pacing/completion timeline at that point. Simply decoding from zero until
`stop_time_ms-1` would make load latency proportional to the movie length; seeking video without matching
audio would replay stale audio during restoration. Once that bounded decoder primitive exists, the rest of
`0x241` can delegate to the existing `0x236` host/surface lifecycle.
The portable implementation delegates graph/surface ownership to the existing `0x236` lifecycle and adds
one synchronous initial-position boundary before decoder workers start. FFmpeg ABI v3 seeks the independent
video and audio demuxers to their preceding indexed packet. Managed video preroll retains the latest frame
at or before the requested position and queues the first later frame, which is essential for
`stop_time_ms-1` to restore the terminal image rather than run off EOF. Audio preroll drops complete earlier
blocks, trims a straddling block at sample precision, and rebases its remaining timestamps with video
pacing/completion to zero. A real archived `CHAPTER.AGF` regression proves both demuxers seek near 11 seconds;
synthetic regressions pin active-frame selection, terminal-frame retention, audio trimming, and pacing.
### Movie-mask transition `0x24d` and tiled-surface edge `0x248` (2026-07-29)