Scripts for processing multichannel audio for playback on Apple TV

multichannel_audio_scripts.md

Multichannel audio-processing scripts for Apple TV

Prerequisites

Apple TV

1. Infuse can play back FLAC and ALAC-encoded multichannel audio wrapped in an MKV container.
2. VLC might play multichannel FLAC without a container. But that stopped working for me when I changed my audio setup to use ARC, so YMMV.

Computer

1. ffmpeg
2. mkvtoolnix
3. cuetools/shntool

Steps

1. If encoded as a single DTS WAV, split into multiple track WAVs from the CUE:

   for i in *.cue; do cue="$i"; wav="`basename "$i" .cue`.wav"; shnsplit -d mkv_audio -f "$cue" -t "%n %t" "$wav"; done;
   

   Note: This will output files to a mkv_audio subdirectory, and if the directory doesn't exist first shnsplit will throw a cryptic error.

2. Convert WAV tracks to either FLAC or ALAC:

   • WAVs to ALAC

     for i in *.wav; do ffmpeg -i "$i" -acodec alac "`basename "$i" .wav`.m4a"; done;
     

   • WAVs to FLAC

     for i in *.wav; do ffmpeg -i "$i" "`basename "$i" .wav`.flac"; done;
     

3. If original tracks are in either FLAC or ALAC, and you want to transcode to the other:

   • FLAC to ALAC

     for i in *.flac; do ffmpeg -i "$i" -acodec alac "`basename "$i" .flac`.m4a"; done;
     

   • ALAC to FLAC

     for i in *.m4a; do ffmpeg -acodec alac -i "$i" "`basename "$i" .m4a`.flac"; done;
     

4. Wrap audio files in MKV container:

   • ALAC to MKV:

     for i in *.m4a; do outfile="`basename "$i" .m4a`.mkv"; mkvmerge "$i" -o "$outfile" ; done;
     

   • FLAC to MKV:

     for i in *.flac; do outfile="`basename "$i" .flac`.mkv"; mkvmerge "$i" -o "$outfile" ; done;
     

5. Remuxing MKVs:

   • FLAC MKV to ALAC MKV:

     for i in *.mkv; do ffmpeg -i "$i" -acodec alac "./output/$i"; done;
     

   • ALAC MKV to FLAC MKV:

     for i in *.mkv; do ffmpeg -i "$i" -c:a flac "./output/$i"; done;
     

Quadraphonic

1. Convert 5.1-encoded audio with empty Center and LFE channels to true 4.0

   for i in *.flac; do ffmpeg -i "$i" -filter_complex "channelmap=0|1|4|5:channel_layout=quad" "./quad_mix/$i"; done;