The following sample file is mono, but exiftool claims has 2 audio channels:
exiftool Bontempi-B3-A3-Chord.m4a
ExifTool Version Number : 12.60
File Name : Bontempi-B3-A3-Chord.m4a
Directory : .
File Size : 33 kB
File Modification Date/Time : 2023:05:27 11:58:39+09:00
File Access Date/Time : 2023:05:27 11:58:40+09:00
File Inode Change Date/Time : 2023:05:27 11:58:39+09:00
File Permissions : -rw-r--r--
File Type : MP4
File Type Extension : mp4
MIME Type : video/mp4
Major Brand : MP4 v2 [ISO 14496-14]
Minor Version : 0.2.0
Compatible Brands : mp42, isom, iso2
Media Data Size : 31951
Media Data Offset : 44
Movie Header Version : 0
Create Date : 0000:00:00 00:00:00
Modify Date : 0000:00:00 00:00:00
Time Scale : 1000
Duration : 1.94 s
Preferred Rate : 1
Preferred Volume : 100.00%
Preview Time : 0 s
Preview Duration : 0 s
Poster Time : 0 s
Selection Time : 0 s
Selection Duration : 0 s
Current Time : 0 s
Next Track ID : 2
Track Header Version : 0
Track Create Date : 0000:00:00 00:00:00
Track Modify Date : 0000:00:00 00:00:00
Track ID : 1
Track Duration : 1.94 s
Track Layer : 0
Track Volume : 100.00%
Matrix Structure : 1 0 0 0 1 0 0 0 1
Media Header Version : 0
Media Create Date : 0000:00:00 00:00:00
Media Modify Date : 0000:00:00 00:00:00
Media Time Scale : 44100
Media Duration : 1.94 s
Media Language Code : und
Handler Description : SoundHandler
Balance : 0
Audio Format : mp4a
Audio Channels : 2
Audio Bits Per Sample : 16
Audio Sample Rate : 44100
Handler Type : Metadata
Handler Vendor ID : Apple
Title : Bontempi B3 A3 Chord
Artist : freewavesamples.com
Encoder : Lavf58.76.100
Avg Bitrate : 132 kbps
This is according to mpv:
mpv Bontempi-B3-A3-Chord.m4a
(+) Audio --aid=1 (*) (aac 1ch 44100Hz)
File tags:
Artist: freewavesamples.com
Title: Bontempi B3 A3 Chord
AO: [coreaudio] 44100Hz mono 1ch floatp
A: 00:00:01 / 00:00:01 (88%)
Exiting... (End of file)
Bontempi-B3-A3-Chord.m4a
Dual mono? (https://producerhawk.com/dual-mono-vs-stereo/)
ExifTool is reporting the metadata written in the file, which may or may not be correctly written by the originating software.
- Phil