Why don’t all Canon MOV metadata tags copy to an M4A file with ExifTool?
Asked 10/17/2020
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2 answers
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I’m extracting audio from a Canon .MOV file to .m4a with ffmpeg, then using ExifTool to copy metadata from the video file into the audio file. Basic metadata copies, but many camera-setting fields do not appear in the M4A afterward, including items like Long Exposure Noise Reduction, ISO Expansion, Live View Shooting, Focus Distance, and other Canon-specific settings.
Commands used:
ffmpeg -i MVI_5918.MOV -vn -ac 1 MVI_5918_p1_mono.m4a exiftool -TagsFromFile MVI_5918.MOV -@ exif2xmp.args MVI_5918_p1_mono.m4a
Why are these tags missing, and is there a way to force ExifTool to copy them into the M4A/XMP metadata?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
5y ago
2 Answers
5
The reason is that those are not EXIF tags, they are MakerNotes. All EXIF tags are Metadata, but not all Metadata are EXIF tags.
When listing data, you should always use the command suggested in ExifTool FAQ #3 so you can see all the information and where it is located. Do so and you'll find that tags such as LongExposureNoiseReduction, ISOExpansion, LCDDisplayAtPowerOn, etc will show up as part of one of the Canon MakerNotes groups (see Canon tags, CanonCustom tags, CanonRaw tags). These tags do not have corresponding tags in the XMP namespace, as they are proprietary to Canon and cannot be simply copied to XMP.
To copy them to XMP, you would have to figure out a existing XMP tag you would want to re-purpose or you could create you're own XMP tags to cover them. But any new tags you create for this would be unlikely to be read by existing programs, as they wouldn't be part of known specs.
Originally by user37960. Source · Licensed CC BY-SA 4.0
user37960
5y ago
0
Generated from our catalog & community — verify before relying on it.
Those missing fields are likely not standard EXIF tags—they’re Canon MakerNotes or related proprietary metadata. ExifTool can read them from the MOV, but when you copy metadata to an M4A using XMP mappings, only tags that have valid destination tags in XMP/QuickTime can be written.
So ExifTool isn’t “dropping” them by mistake; many Canon-specific camera settings simply have no corresponding standard XMP tags to copy into.
To confirm where tags live, use ExifTool’s detailed group output (as recommended in the ExifTool FAQ) so you can see whether a field is EXIF, MakerNotes, CanonCustom, CanonRaw, etc.
If you need to preserve those proprietary values, your options are limited:
- keep the original MOV metadata alongside the file,
- copy only the standard tags that have valid destinations, or
- define/customize your own XMP tags and map those Canon values into them.
In short: you can’t force standard XMP copying to preserve Canon MakerNotes unless you create custom tag mappings.
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