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[FIX] Compute FFmpeg tx3g end time in one step - #2387
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#2378 derives the end of a tx3g cue as start_ms + duration * 1000 / timescale. Both terms are truncated separately, so the end can land 1 ms before the GPAC path's, which converts pts + duration at once. On a real m4v with 797 cues, 99 ended 1 ms early (e.g. timescale 600, pts 135725, duration 2725: 230749 instead of 230750).
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Repro instructions:
Build with
-DWITH_FFMPEG=ONand extract thetx3gtrack of sample 162 on the sample platform (Yomeddine_1080p_HD, m4v, 797 cues) with--out=srt; compare against the default (GPAC) build.Follow-up to #2378. It derives a cue's end as
start_ms + pkt.duration * 1000 / timescale; both terms are truncated separately, so the end can land 1 ms before the GPAC path, which convertspts + durationin one step. On sample 162, 99 of 797 cues ended 1 ms early (e.g. timescale 600, pts 135725, duration 2725 → 230749 instead of 230750). This computes(pts + pkt.duration) * 1000 / timescale.Verified: on the FFmpeg build,
--out=srtoutput is now byte-identical to the GPAC build on sample 162 and on five synthetictx3gfiles (video + subtitle, subtitle-only,texthandler, #2378's own sample, and one with a cue at 0 plus contiguous and overlapping cues).cargo fmt --checkandcargo clippy --features enable_mp4_ffmpeg -- -D warningsare clean.