Creating Core Audio Format (.caf) Files

Q: I'm trying to author Core Audio Format files using QuickTime Player but it doesn't have a .caf file exporter. How can I create .caf files on Mac OS X?

A: While QuickTime supports importing Core Audio Format (.caf) files, it does not currently provide an audio exporter capable of creating these files.

The easiest way to create a Core Audio Format file is by using the afconvert tool located in /usr/bin/.

afconvert (a.k.a. Audio File Convert) will convert a source audio file to a new audio file and supports a large set of file formats, data formats and encoding options.

For example, Listing 1 demonstrates how you might use afconvert from the Terminal to create a .caf file containing AAC audio encoded with an average data rate of 192kbps.

Listing 1: Convert an .aif file to a .caf file.

afconvert -v -f 'caff' -d aac -s 1 -b 192000 MySource.aif MyOutput.caf
NAME
     afconvert -- Audio File Convert

SYNOPSIS
     afconvert [option...] input_file [output_file]

DESCRIPTION
     Audio File Convert will convert a source audio file to a new audio file of the specified file type containing audio data of the specified data type.

OPTIONS (may appear before or after arguments)
     { -f | --file } file_format:
        '3gpp' = 3GP Audio (.3gp)
                   data_formats: 'aac ' 'samr' 
        '3gp2' = 3GPP2 Audio (.3g2)
                   data_formats: 'aac ' 'samr' 
        'adts' = AAC ADTS (.aac, .adts)
                   data_formats: 'aac ' 
        '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' 
        'caff' = Apple CAF (.caf)
                   data_formats: '.mp1' '.mp2' '.mp3' 'MAC3' 'MAC6' 
                                 'QDM2' 'QDMC' 'Qclp' 'Qclq' 'aac ' 'aacl' 
                                 'agsm' 'alac' 'alaw' 'drms' 'dvca' 'dvi ' 
                                 'dvi8' 'ilbc' 'ima4' 'lpc ' I8 BEI16 
                                 BEI24 BEI32 BEF32 BEF64 LEI16 LEI24 
                                 LEI32 LEF32 LEF64 'ms\x00\x02' 'ms\x00\x11' 'ms\x001' 
                                 'ms\x00U' 'samr' 'ulaw' 'vdva' 
        'MPG1' = MPEG Layer 1 (.mp1, .mpeg, .mpa)
                   data_formats: '.mp1' 
        'MPG2' = MPEG Layer 2 (.mp2, .mpeg, .mpa)
                   data_formats: '.mp2' 
        'MPG3' = MPEG Layer 3 (.mp3, .mpeg, .mpa)
                   data_formats: '.mp3' 
        'mp4f' = MPEG4 Audio (.mp4)
                   data_formats: 'aac ' 'aacl' 
        'm4af' = MPEG4 Audio (.m4a)
                   data_formats: 'aac ' 'aacl' 'alac' 
        'NeXT' = NeXT/Sun (.snd, .au)
                   data_formats: I8 BEI16 BEI24 BEI32 BEF32 
                                 BEF64 'ulaw' 
        'Sd2f' = Sound Designer II (.sd2)
                   data_formats: I8 BEI16 BEI24 BEI32 
        'WAVE' = WAVE (.wav)
                   data_formats: UI8 LEI16 LEI24 LEI32 LEF32 
                                 LEF64 'ulaw' 'alaw' 
    { -d | --data } data_format[@sample_rate_hz][/format_flags][#frames_per_packet] :
        [-][BE|LE]{F|[U]I}{8|16|24|32|64} (PCM)
            e.g. BEI16   F32@44100
        or a data format appropriate to file format, as above
        format_flags: hex digits, e.g. '80'
        Frames per packet can be specified for some encoders, e.g.: samr#12
    { -c | --channels } number_of_channels
        add/remove channels without regard to order
    { -l | --channellayout } layout_tag
        layout_tag: name of a constant from CoreAudioTypes.h
          (prefix "kAudioChannelLayoutTag_" may be omitted)
        if specified once, applies to output file; if twice, the first
          applies to the input file, the second to the output file
    { -b | --bitrate } bit_rate_bps
         e.g. 128000
    { -q | --quality } codec_quality
        codec_quality: 0-127
    { -r | --src-quality } src_quality
        src_quality (sample rate converter quality): 0-127
    { --src-complexity } src_complexity
        src_complexity (sample rate converter complexity): line, norm, bats
    { -v | --verbose }
        print progress verbosely
    { -s | --strategy } strategy
        bitrate allocation strategy for encoding an audio track
        0 for CBR, 1 for ABR, 2 for VBR_constrained, 3 for VBR
    { -t | --tag }
        If encoding to CAF, store the source file's format and name in a user chunk.
        If decoding from CAF, use the destination format and filename found in a user chunk.
    --read-track track_index
        For input files containing multiple tracks, the index (0..n-1) of the track
        to read and convert.
    --prime-method method
        decode priming method (see AudioConverter.h)
    --no-filler
        don't page-align audio data in the output file
    { -u | --userproperty } property value
        set an arbitrary property to a given value
        property must be a four char code
        value is a signed 32-bit integer
        A maximum of 8 properties may be set
        e.g. use '-u vbrq <sound_quality>' to set the sound quality level (<sound_quality>: 0-127) 
             for VBR encoding strategy (i.e., -s 3) 
    { -h | --help }
        print help

References

Introduction to Apple Core Audio Format Specification

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Document Revision History

Date Notes
2009-01-07 First Version

Posted: 2009-01-07

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