NAME

Audio::Sndfile - read/write audio data via libsndfile

SYNOPSIS

    # Convert file to 32 bit float WAV

    use Audio::Sndfile;

    my $in = Audio::Sndfile.new(filename => "t/data/cw_glitch_noise15.wav", :r);

    my $out-format = Audio::Sndfile::Info::WAV +| Audio::Sndfile::Info::FLOAT;

    my $out = Audio::Sndfile.new(filename   => "out.wav", :w,
                                channels   => $in.channels,
                                samplerate => $in.samplerate,
                                format     => $out-format);

    loop {
        my @in-frames = $in.read-float(1024);
        $out.write-float(@in-frames);
        last if ( @in-frames / $in.channels ) != 1024;
    }

    $in.close;
    $out.close;

Other examples are available in the "examples" sub-directory of the repository.

DESCRIPTION

This library provides a mechanism to read and write audio data files in various formats by using the API provided by libsndfile.

A full list of the formats it is able to work with can be found at:

http://www.mega-nerd.com/libsndfile/#Features

if you need to work with formats that aren't listed then you will need to find another library.

The interface presented is slightly simplified with regard to that of libsndfile and whilst it does nearly everything I need it do, I have opted to release the most useful functionality early and progressively add features as it becomes clear how they should be implemented.

As of the first release, the methods provided for writing audio data do not constrain the items to the range expected by the method. If out of range data is supplied wrapping will occur which may lead to unexpected results.

FRAMES vs ITEMS

In the description of the methods below a 'frame' refers to one or more items ( that is the number of channels in the audio data.) The frame data is interleaved per channel consecutively and must always have a number of items that is a multiple of the number of channels. The read methods will always return a number of items that is the multiple of number of channels - thus you can determine if you got the number back that you requested with something like:

@frames.elems == ( $num-channels * $frames-requested)

The write methods will throw an exception if supplied with an array that isn't some multiple of the number of channels and will always return the number of 'frames' written.

There are no methods provided for interleaving or de-interleaving frame data as Raku's list methods (e.g. zip or rotor) are perfect for this task.

METHODS

new

method new(Audio::Sndfile:U: Str :$filename!, :r)

The :r adverb opens the specified file for reading. If the file can't be opened or there is some other problem with it (such as it not being a supported format,) then an exception will be thrown.

method new(Audio::Sndfile:U: Str :$filename!, :w, Audio::Sndfile::Info :$info)
method new(Audio::Sndfile:U: Str :$filename!, :w, *%info)

The :w adverb opens the specified file for writing. It requires either an existing valid Audio::Sndfile::Info supplied as the info named parameter, or attributes that will be passed to the constructor of Audio::Sndfile::Info. If the file cannot be opened for some reason or the resulting Audio::Sndfile::Info is incomplete or invalid an exception will be thrown.

The info requires the attributes channels, format, samplerate. If copying or converting an existing file opened for reading the clone-info method can be used to obtain a valid Audio::Sndfile::Info.

info

This is an accessor to the Audio::Sndfile::Info for the opened file. It is read-only as it doesn't make sense to change the info after the file has been opened.

There are several accessors delegated to this object:

• format

The format of the file formed by the bitwise or of type, sub-type and endian

• channels

The number of channels in the file.

• samplerate

The sample rate of the file as an Int (e.g. 44100, 48000).

• frames

The number of frames in the file. This only makes sense when the file is opened for reading.

• sections

• seekable

A Bool indicating whether the open file is seekable, this will be True for most regular files and False for special files such as a pipe, however as there currently isn't any easy way to open other than a regular file this may not be useful.

• type

A value of the enum Audio::Sndfile::Info::Format indicating the major format of the file (e.g. WAV,) this is bitwise or-ed with the sub-type and endian to create format (which is what is used by the underlying library functions.)

• sub-type

A value of the enum Audio::Sndfile::Info::Subformat indicating the minor format or sample encoding of the file (e.g PCM_16, FLOAT, ) this is bitwise or-ed with the type and endian to create format

• endian

A value of the enum Audio::Sndfile::Info::End that indicate the endian-ness of the sample data. This is bitwise or-ed with type and sub-type to provide format.

• duration

A Duration object that describes the duration of the file in (possibly fractional) seconds. This probably only makes sense for files opened for reading.

library-version

method library-version(Audio::Sndfile:D: ) returns Str

Returns a string representation of the version reported by libsndfile.

close

method close(Audio::Sndfile:D:) returns Int

This closes the file stream for the opened file. Attempting to write or read the object after this has been called is an error.

error-number

method error-number(Audio::Sndfile:D:) returns Int

This returns non-zero if there was an error in the last read, write or open operation. The actual error message can be obtained with error below.

error

method error(Audio::Sndfile:D:) returns Str

This will return the string describing the last error if error-number was non-zero or 'No Error' otherwise.

sync

method sync(Audio::Sndfile:D:) returns Int

If the file is opened for writing then any buffered data will be flushed to disk. If the file was opened for reading it does nothing.

read-short

multi method read-short(Audio::Sndfile:D: Int $frames) returns Array[int16]
multi method read-short(Audio::Sndfile:D: Int $frames, :$raw!) returns [CArray[int16], Int]

This returns an array of size $frames * $num-channels of 16 bit integers from the opened file. The returned array may be empty or shorter than expected if there is no more data to read.

With the the ':raw' adverb specified it will return a two element array containing the raw CArray returned from the underlying library and the number of frames. This is for convenience (and efficiency ) where the data is going to be passed directly to another native libray function.

write-short

multi method write-short(Audio::Sndfile:D: @frames) returns Int
multi method write-short(Audio::Sndfile:D: CArray[int16] $frames-in, Int $frames) returns Int

This writes the array @frames of 16 bit integers to the file. @frames must have a number of elements that is a multiple of the number of channels or an exception will be thrown.

If the files isn't opened for writing or if it has been closed an error will occur.

If the values are outside the range for an int16 then wrapping will occur.

The second multi is for the convenience of applications which may have obtained their data from some native function.

read-int

multi method read-int(Audio::Sndfile:D: Int $frames) returns Array[Int]
multi method read-int(Audio::Sndfile:D: Int $frames, :$raw!) returns [CArray[int32], Int]

This returns an array of size $frames * $num-channels of 32 bit integers from the opened file. The returned array may be empty or shorter than expected if there is no more data to read.

With the the ':raw' adverb specified it will return a two element array containing the raw CArray returned from the underlying library and the number of frames. This is for convenience (and efficiency ) where the data is going to be passed directly to another native libray function.

write-int

multi method write-int(Audio::Sndfile:D: @frames) returns Int
multi method write-int(Audio::Sndfile:D: CArray[int32] $frames-in, Int $frames) returns Int

This writes the array @frames of 32 bit integers to the file. @frames must have a number of elements that is a multiple of the number of channels or an exception will be thrown.

If the files isn't opened for writing or if it has been closed an error will occur.

If the values are outside the range for an int32 then wrapping will occur.

The second multi is for the convenience of applications which may have obtained their data from some native function.

read-float

multi method read-float(Audio::Sndfile:D: Int $frames) returns Array[num32]
multi method read-float(Audio::Sndfile:D: Int $frames, :$raw!) returns [CArray[num32], Int]

This returns an array of size $frames * $num-channels of 32 bit floating point numbers from the opened file. The returned array may be empty or shorter than expected if there is no more data to read.

With the the ':raw' adverb specified it will return a two element array containing the raw CArray returned from the underlying library and the number of frames. This is for convenience (and efficiency ) where the data is going to be passed directly to another native libray function.

write-float

multi method write-float(Audio::Sndfile:D: @frames) returns Int
multi method write-float(Audio::Sndfile:D: CArray[num32] $frames-in, Int $frames) returns Int

This writes the array @frames of 32 bit floating point numbers to the file. @frames must have a number of elements that is a multiple of the number of channels or an exception will be thrown.

If the files isn't opened for writing or if it has been closed an error will occur.

If the values are outside the range for a num32 then wrapping will occur.

The second multi is for the convenience of applications which may have obtained their data from some native function.

read-double

multi method read-double(Audio::Sndfile:D: Int $frames) returns Array[num64]
multi method read-double(Audio::Sndfile:D: Int $frames, :$raw!) returns [CArray[num64], Int]

This returns an array of size $frames * $num-channels of 64 bit floating point numbers from the opened file. The returned array may be empty or shorter than expected if there is no more data to read.

With the the ':raw' adverb specified it will return a two element array containing the raw CArray returned from the underlying library and the number of frames. This is for convenience (and efficiency ) where the data is going to be passed directly to another native libray function.

write-double

multi method write-double(Audio::Sndfile:D: @frames) returns Int
multi method write-double(Audio::Sndfile:D: CArray[num64] $frames-in, Int $frames) returns Int

This writes the array @frames of 64 bit floating point numbers to the file. @frames must have a number of elements that is a multiple of the number of channels or an exception will be thrown.

If the files isn't opened for writing or if it has been closed an error will occur.

If the values are outside the range for a num64 then wrapping will occur.

As of the time of the initial release, this may fail if the frame data was directly retrieved via read-double due to an infelicity in the runtime, this should be fixed at some point but can be worked around by copying the values.

The second multi is for the convenience of applications which may have obtained their data from some native function.

clone-info

method clone-info(Audio::Sndfile:D: ) returns Audio::Sndfile::Info

This returns a new Audio::Sndfile::Info based on the details of the current file suitable for being passed to new for instance when copying or converting the file.