Unable to convert some audio formats

[tryWabbit]

Thank you for creating this beautiful library, It is really helpful for other developers.

I'm trying to convert an m4a file to some formats and but it is throwing me an error:-

Code I'm using:-

let inputURL = audioUrl!
let outputURL = URL(fileURLWithPath: NSTemporaryDirectory() + "trimmed.aifc")
print(inputURL)
print(outputURL)
if FileManager.default.fileExists(atPath: outputURL.path) {
    try? FileManager.default.removeItem(atPath: outputURL.path)
}
do {
    try AudioConverter.convert(inputURL, to: outputURL)
} catch let error {
    print(error)
}

When I try to convert .m4a to .aifc I get

2023-10-07 17:27:42.978255+0530 RPTools[45431:2069254] [AMCP]  91395          HALC_ProxyIOContext.cpp:1329  HALC_ProxyIOContext::IOWorkLoop: skipping cycle due to overload
2023-10-07 17:27:42.987289+0530 RPTools[45431:2068879] [AudioEncoder] SFBAudioEncodingSettingsKeyCoreAudioFileTypeID is not set: guessed 'AIFC' based on extension "aifc"
2023-10-07 17:27:42.987459+0530 RPTools[45431:2068879] [AudioEncoder] SFBAudioEncodingSettingsKeyCoreAudioFormatID is not set: guessed 'lpcm' based on format 'AIFC'
2023-10-07 17:27:42.987533+0530 RPTools[45431:2068879] [AudioEncoder] SFBAudioEncodingSettingsKeyCoreAudioFormatFlags is not set; mFormatFlags will be zero which is probably incorrect
2023-10-07 17:27:42.987619+0530 RPTools[45431:2068879] [AudioEncoder] SFBAudioEncodingSettingsKeyCoreAudioBitsPerChannel is not set; mBitsPerChannel will be zero which is probably incorrect
2023-10-07 17:27:42.987676+0530 RPTools[45431:2068879] [AudioEncoder] AudioFileOpenWithCallbacks failed: 1718449215 'fmt?'
Error Domain=NSOSStatusErrorDomain Code=1718449215 "(null)"
2023-10-07 17:27:49.140740+0530 RPTools[45431:2069254] [AMCP]  91395          HALC_ProxyIOContext.cpp:1329  HALC_ProxyIOContext::IOWorkLoop: skipping cycle due to overload

Same error I get with ac3 and eac3.

Any help will be truly appreciated.

[sbooth]

The problem is that encoders can't necessarily deduce what the desired output format is based on the input format, and rather than guessing an error is thrown. For example, compressed audio typically has no bits per channel. When converting to PCM, what bits per channel value is desired by the caller? There is no way to know.

For the Core Audio encoder there are many supported formats and the possibilities for matching input and output formats are numerous. With this in mind, the caller often needs to provide more information on what format is desired and the log states as much:

2023-10-07 17:27:42.987533+0530 RPTools[45431:2068879] [AudioEncoder] SFBAudioEncodingSettingsKeyCoreAudioFormatFlags is not set; mFormatFlags will be zero which is probably incorrect
2023-10-07 17:27:42.987619+0530 RPTools[45431:2068879] [AudioEncoder] SFBAudioEncodingSettingsKeyCoreAudioBitsPerChannel is not set; mBitsPerChannel will be zero which is probably incorrect

To perform the conversion to AIFC it's necessary to set the format flags and bits per channel on the encoder:

let encoder = try AudioEncoder(url: destURL, encoderName: .coreAudio)
encoder.settings = [
	.coreAudioBitsPerChannel: 16,
	.coreAudioFormatFlags: kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsBigEndian | kAudioFormatFlagIsPacked
]
let converter = try AudioConverter(url: url, encoder: encoder)
try converter.convert()

[tryWabbit]

Thank you so much for the quick reply @sbooth It worked like a charm.

Due to my limited knowledge, I'm also having issues converting the format to ac3 and eac3. I know this solution I can provide settings for ac3 and eac3 manually but I haven't found them yet, if you already know the settings for those two formats it would be a great help otherwise I will continue my research and will eventually find something.

Thank you so much for the help again, I really appreciate it.

[sbooth]

The afconvert command-line tool may be used to show Core Audio's supported file and data formats:

% afconvert -hf
Audio file and data formats:
    '3gpp' = 3GP Audio (.3gp, .3gpp)
               data_formats: 'aac ' 'aace' 'aacf' 'aacg' 'aach' 'aacl' 
                             'aacp' 'samr' 
    '3gp2' = 3GPP-2 Audio (.3g2, .3gp2)
               data_formats: 'aac ' 'aace' 'aacf' 'aacg' 'aach' 'aacl' 
                             'aacp' 'samr' 
    'adts' = AAC ADTS (.aac, .adts)
               data_formats: 'aac ' 'aach' 'aacp' 
    'ac-3' = AC3 (.ac3)
               data_formats: 'ac-3' 
    'AIFC' = AIFC (.aifc, .aiff, .aif)
               data_formats: I8 BEI16 BEI24 BEI32 BEF32 BEF64 UI8 'ulaw' 
                             'alaw' 'MAC3' 'MAC6' 'ima4' 'QDMC' 'QDM2' 
                             'Qclp' 'agsm' 
    'AIFF' = AIFF (.aiff, .aif)
               data_formats: I8 BEI16 BEI24 BEI32 
    'amrf' = AMR (.amr)
               data_formats: 'samr' 'sawb' 
    'm4af' = Apple MPEG-4 Audio (.m4a, .m4r)
               data_formats: '.mp1' '.mp2' '.mp3' 'aac ' 'aace' 'aacf' 
                             'aacg' 'aach' 'aacl' 'aacp' 'ac-3' 'alac' 
                             'ec-3' 'flac' 'paac' 'pac3' 'pec3' 
    'm4bf' = Apple MPEG-4 AudioBooks (.m4b)
               data_formats: 'aac ' 'aace' 'aacf' 'aacg' 'aach' 'aacl' 
                             'aacp' 'paac' 
    'caff' = CAF (.caf, .caff)
               data_formats: '.mp1' '.mp2' '.mp3' 'aac ' 'aace' 'aacf' 
                             'aacg' 'aach' 'aacl' 'aacp' 'ac-3' 'alac' 
                             'alaw' 'apac' 'dvi8' 'ec-3' 'flac' 'ilbc' 
                             'ima4' I8 BEI16 BEI24 BEI32 BEF32 BEF64 LEI16 
                             LEI24 LEI32 LEF32 LEF64 'ms\x00\x02' 'ms\x00\x11' 
                             'ms\x001' 'opus' 'paac' 'pac3' 'pach' 'pacp' 
                             'pec3' 'pusa' 'qaac' 'qac3' 'qach' 'qacp' 
                             'qapc' 'qec3' 'qflc' 'qlac' 'qusa' 'samr' 
                             'ulaw' 'usac' 'zaac' 'zac3' 'zach' 'zacp' 
                             'zec3' 'zlac' 
    'ec-3' = EC3 (.ec3, .eac3)
               data_formats: 'ec-3' 
    'flac' = FLAC (.flac)
               data_formats: 'flac' 
    'loas' = LATM/LOAS (.loas, .latm, .xhe)
               data_formats: 'aac ' 'aace' 'aacf' 'aacg' 'aach' 'aacl' 
                             'aacp' 'usac' 
    'MPG1' = MPEG Layer 1 (.mp1, .mpeg, .mpa, .m1a, .m2a)
               data_formats: '.mp1' 
    'MPG2' = MPEG Layer 2 (.mp2, .mpeg, .mpa, .m1a, .m2a)
               data_formats: '.mp2' 
    'MPG3' = MPEG Layer 3 (.mp3, .mpeg, .mpa, .m1a, .m2a)
               data_formats: '.mp3' 
    'mp4f' = MPEG-4 Audio (.mp4, .mpg4)
               data_formats: '.mp1' '.mp2' '.mp3' 'aac ' 'aace' 'aacf' 
                             'aacg' 'aach' 'aacl' 'aacp' 'ac-3' 'alac' 
                             'apac' 'ec-3' 'flac' LEF32 BEF32 LEF64 BEF64 
                             LEI32 BEI32 UI0 UI0 UI0 UI0 'opus' 'paac' 
                             'pac3' 'pach' 'pacp' 'pec3' 'pusa' 'qaac' 
                             'qac3' 'qach' 'qacp' 'qapc' 'qec3' 'qflc' 
                             'qlac' 'qusa' 'usac' 
    'NeXT' = NeXT/Sun (.snd, .au)
               data_formats: I8 BEI16 BEI24 BEI32 BEF32 BEF64 'ulaw' 'alaw' 
    'Sd2f' = Sound Designer II (.sd2)
               data_formats: I8 BEI16 BEI24 BEI32 
    'WAVE' = WAVE (.wav)
               data_formats: UI8 LEI16 LEI24 LEI32 LEF32 LEF64 'ulaw' 
                             'alaw' 'ms\x00\x11' 'ms\x00\x02' 'ms\x001' 
    'BW64' = WAVE (BW64 for length over 4 GB) (.wav)
               data_formats: UI8 LEI16 LEI24 LEI32 LEF32 LEF64 'ulaw' 
                             'alaw' 'ms\x00\x11' 'ms\x00\x02' 'ms\x001' 
    'RF64' = WAVE (RF64 for length over 4 GB) (.wav)
               data_formats: UI8 LEI16 LEI24 LEI32 LEF32 LEF64 'ulaw' 
                             'alaw' 'ms\x00\x11' 'ms\x00\x02' 'ms\x001' 
    'W64f' = Wave64 (.w64)
               data_formats: UI8 LEI16 LEI24 LEI32 LEF32 LEF64 'ulaw' 
                             'alaw' 'ms\x00\x11' 'ms\x00\x02' 'ms\x001' 

These are all the formats supported for either encoding or decoding.

You can get a list of available formats for encoding using AudioFormatGetProperty with the property kAudioFormatProperty_EncodeFormatIDs. On my system the list is

Format ID	Constant
'aac '	kAudioFormatMPEG4AAC
'aace'	kAudioFormatMPEG4AAC_ELD
'aacf'	kAudioFormatMPEG4AAC_ELD_SBR
'aacg'	kAudioFormatMPEG4AAC_ELD_V2
'aach'	kAudioFormatMPEG4AAC_HE
'aacl'	kAudioFormatMPEG4AAC_LD
'aacp'	kAudioFormatMPEG4AAC_HE_V2
'alac'	kAudioFormatAppleLossless
'alaw'	kAudioFormatALaw
'flac'	kAudioFormatFLAC
'ilbc'	kAudioFormatiLBC
'ima4'	kAudioFormatAppleIMA4
'lpcm'	kAudioFormatLinearPCM
'opus'	kAudioFormatOpus
'ulaw'	kAudioFormatULaw

So I don't believe AC-3 (kAudioFormatAC3) or Enhanced AC-3 (kAudioFormatEnhancedAC3) encoders are available.

[sbooth]

There is a private function in SFBCoreAudioEncoder.mm named AudioFormatIDsForFileTypeID() that might be useful.

SFBAudioEngine/Encoders/SFBCoreAudioEncoder.mm

Line 62 in a6df55e

std::vector<AudioFormatID> AudioFormatIDsForFileTypeID(AudioFileTypeID fileTypeID, bool forEncoding = false)

It takes an AudioFileTypeID and returns a list of supported AudioFormatIDs.

[tryWabbit]

Thank you so much for all the help @sbooth