Multichannel ALAC misidentified as stereo by mkvinfo after muxing into MKV
I'm testing this on a Mac with ffmpeg version 4.1 and mkvmerge/mkvinfo v40.0.0 ('Old Town Road + Pony') 64-bit.
Wrap a 5.1 ALAC file into an MKV container:
mkvmerge mdl -o "Channel Test (5.1).mkv". This file plays back with all 6 channels.
However, mkvinfo misidentifies the number of audio channels:
mkvinfo "Channel Test (5.1).mkv"
... |+ Tracks | + Track | + Track number: 1 (track ID for mkvmerge & mkvextract: 0) | + Track UID: 3084434016894002583 | + Track type: audio | + Codec ID: A_ALAC | + Codec's private data: size 24 | + Language: und | + Audio track | + Sampling frequency: 44100 | + Channels: 2 ...
The correct number of channels can be identified in original ALAC file:
mdls "Channel Test (5.1).m4a"
MDItemAlbum = "Channel Test Tracks" kMDItemAlternateNames = ( "Channel Test (5.1).m4a" ) kMDItemAudioBitRate = 312150 kMDItemAudioChannelCount = 6 ...
The same problem does not occur if the original audio source is a 5.1 FLAC file. mkvinfo correctly identifies the audio track as 6 channels.