H.264 streams that redefine the same pic_parameter_set_id in-band with
different content cannot be safely stream-copied into an avc1/fMP4 HLS
segment: the avcC advertises a single parameter set, so VideoToolbox
(Safari/Chrome on macOS) decodes with the wrong PPS and desyncs mid-GOP,
surfacing as PIPELINE_ERROR_DECODE / kVTVideoDecoderBadDataErr (-12909).
At playback start, a bitstream scan (DetectMultiplePPSH264) runs for H.264
files on the probe-ensure path, grouping in-band PPS by id and flagging any
id carrying more than one distinct definition. The result is a runtime-only
flag (VideoTrack.MultiplePPS, json:"-") memoized per process — never written
to the database, no schema change, recomputed on the first play after a
restart.
The v3 planner and legacy resolver disqualify a copy-unsafe source from the
video stream-copy / remux ladder, routing it to a real transcode. Direct
play of the original container is left intact: decoders that reparse in-band
parameter sets (ExoPlayer, VLC, native) handle the source fine.
Part of #135.
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