Extracting RIFF data from both .wav and .flac files
Wave files can contain unofficial metadata, such as Sampler Chunk - "smpl": https://sites.google.com/site/musicgapi/technical-documents/wav-file-format#smpl
These are used for audio looping players and samplers avoiding to loading multiple samples.
I have one such file here:
and a flac file converted using the official flac command line tool:
flac harmonica_1.wav --keep-foreign-metadata
https://github.com/studiorack/basic-harmonica/blob/main/samples/harmonica_1.flac
When running these tools I can confirm the metadata exists in each file:
However I do see a different in the number of bytes (I believe as flac has riff inserted in multiple places)
I can also convert the .flac file back to .wav and it is the same size, and contains the metadata: flac harmonica_1.flac --keep-foreign-metadata
When using other tools I can read the data:
$ sndfile-info har.wav
smpl : 60
Manufacturer : 0
Product : 0
Period : 20833 nsec
Midi Note : 64
Pitch Fract. : 0
SMPTE Format : 0
SMPTE Offset : 00:00:00 00
Loop Count : 1
Cue ID : 131072 Type : 0 Start : 12707 End : 47221 Fraction : 0 Count : 0
Sampler Data : 0
https://linux.die.net/man/1/sndfile-info
This only works for .wav files. There is a feature request for libsndfile to support 'smpl' in flac files: https://github.com/libsndfile/libsndfile/issues/59
$ metaflac ./har.flac --list
smpl<aQ@�1u�METADATA block #7
type: 2 (APPLICATION)
is last: false
length: 20
application ID: 72696666
data contents:
However as you can see the result returned are different. I would like a both .wav and .flac RIFF 'smpl' data to be returned in the same format, so I can verify the results match.
https://exiftool.org appears to be tool to do that. But it also produced inconsistent results between .wav and .flac:
$ exiftool -a -G1 -s ./har.wav
[ExifTool] ExifToolVersion : 12.42
[System] FileName : har.wav
[System] Directory : .
[System] FileSize : 95 kB
[System] FileModifyDate : 2022:10:11 21:16:37-07:00
[System] FileAccessDate : 2022:10:15 14:39:46-07:00
[System] FileInodeChangeDate : 2022:10:15 14:39:50-07:00
[System] FilePermissions : -rw-r--r--
[File] FileType : WAV
[File] FileTypeExtension : wav
[File] MIMEType : audio/x-wav
[RIFF] Encoding : Microsoft PCM
[RIFF] NumChannels : 1
[RIFF] SampleRate : 48000
[RIFF] AvgBytesPerSec : 96000
[RIFF] BitsPerSample : 16
[RIFF] Manufacturer : 0
[RIFF] Product : 0
[RIFF] SamplePeriod : 20833
[RIFF] MIDIUnityNote : 64
[RIFF] MIDIPitchFraction : 0
[RIFF] SMPTEFormat : none
[RIFF] SMPTEOffset : 00:00:00:00
[RIFF] NumSampleLoops : 1
[RIFF] SamplerDataLen : 0
[RIFF] SamplerData : (Binary data 20 bytes, use -b option to extract)
[RIFF] UnshiftedNote : 64
[RIFF] FineTune : 0
[RIFF] Gain : 0
[RIFF] LowNote : 0
[RIFF] HighNote : 127
[RIFF] LowVelocity : 0
[RIFF] HighVelocity : 127
[RIFF] Comment : Recorded on 7/10/2022 in Edison.
[RIFF] Software : FL Studio 20
[Composite] Duration : 0.99 s
and for flac
$ exiftool -a -G1 -s ./har.flac
[ExifTool] ExifToolVersion : 12.42
[System] FileName : har.flac
[System] Directory : .
[System] FileSize : 83 kB
[System] FileModifyDate : 2022:10:11 20:59:37-07:00
[System] FileAccessDate : 2022:10:15 14:44:12-07:00
[System] FileInodeChangeDate : 2022:10:15 14:42:26-07:00
[System] FilePermissions : -rw-r--r--
[File] FileType : FLAC
[File] FileTypeExtension : flac
[File] MIMEType : audio/flac
[FLAC] BlockSizeMin : 4096
[FLAC] BlockSizeMax : 4096
[FLAC] FrameSizeMin : 3442
[FLAC] FrameSizeMax : 6514
[FLAC] SampleRate : 48000
[FLAC] Channels : 1
[FLAC] BitsPerSample : 16
[FLAC] TotalSamples : 47222
[FLAC] MD5Signature : f89646c0d3056ec38c3e33ca79299253
[Vorbis] Vendor : reference libFLAC 1.4.1 20220922
[Composite] Duration : 0.98 s
How can I read this data consistently regardless of .flac or .wav file?
I was helped by the creator of exiftool here: https://exiftool.org/forum/index.php?topic=14064.0
In short flac riff blocks were stored in a custom metadata format which exiftool could parse but needed a custom .ExifTool_config file
The creator added the necessary changes in a commit: https://github.com/exiftool/exiftool/commit/5c2467fa6cdb38233793884e80cee9abf4da48e6#diff-0c24c6846e8207ad8d090e564fdc366dad6386f2ef7c51eea5aa0d72d970ff11
The latest release of ExifTool 12.49 now parses .wav and .flac loop data! "Decode 'riff' metadata blocks in FLAC audio files" https://exiftool.org/history.html
Usage:
exiftool ./har.wav
exiftool ./har.flac
Output:
Encoding : Microsoft PCM
Num Channels : 1
Sample Rate : 48000
Avg Bytes Per Sec : 96000
Bits Per Sample : 16
Manufacturer : 0
Product : 0
Sample Period : 20833
MIDI Unity Note : 64
MIDI Pitch Fraction : 0
SMPTE Format : none
SMPTE Offset : 00:00:00:00
Num Sample Loops : 1
Sampler Data Len : 0
Sampler Data : (Binary data 20 bytes, use -b option to extract)
Unshifted Note : 64
Fine Tune : 0
Gain : 0
Low Note : 0
High Note : 127
Low Velocity : 0
High Velocity : 127
Acidizer Flags : One shot
Root Note : High C
Beats : 2
Meter : 4/4
Tempo : 0
Comment : Recorded on 7/10/2022 in Edison.
Software : FL Studio 20
Duration : 0.87 s
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