FFprobe sets the codec; DTS goes to .mka, PCM to .flac or .wav, AC-4/MPEG-H/DTS-UHD to MP4Box. The remux also cuts --sample, --no-mux no longer applies to a Song, and the tagger adds cover fallback, WebP, ARTISTS and ReplayGain. Song tag data now reaches a --remote client.
A song skips the muxer, so the decrypted fragmented MP4 was the delivered file: its header states a length of zero and FLAC in an MP4 is not a FLAC stream, so playback stopped early and tagging failed.
Group selected videos by (resolution, range, codec) and mux each group into one MKV; only language is collapsed, so ranges/codecs/resolutions stay in separate files. Adds --merge-video flag + muxing.merge_video config (global and per-service), docs, and tests.
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