IIRC, in many containers embedded subtitles will be interleaved with the video and audio atoms/boxes/packets/etc., and so pulling out the subtitles requires sca

IIRC, in many containers embedded subtitles will be interleaved with the video and audio atoms/boxes/packets/etc., and so pulling out the subtitles requires scanning the full file. Not quite as expensive as decoding or re-encoding, but still as slow as "stream the full file into memory and demux the streams"