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juce::MemoryMappedAudioFormatReader Class Referenceabstract

A specialised type of AudioFormatReader that uses a MemoryMappedFile to read directly from an audio file. More...

#include <juce_MemoryMappedAudioFormatReader.h>

Inheritance diagram for juce::MemoryMappedAudioFormatReader:
Collaboration diagram for juce::MemoryMappedAudioFormatReader:

Public Member Functions

virtual AudioChannelSet getChannelLayout ()
 Get the channel layout of the audio stream. More...
 
const FilegetFile () const noexcept
 Returns the file that is being mapped. More...
 
const StringgetFormatName () const noexcept
 Returns a description of what type of format this is. More...
 
Range< int64getMappedSection () const noexcept
 Returns the sample range that's currently memory-mapped and available for reading. More...
 
size_t getNumBytesUsed () const
 Returns the number of bytes currently being mapped. More...
 
virtual void getSample (int64 sampleIndex, float *result) const noexcept=0
 Returns the samples for all channels at a given sample position. More...
 
bool mapEntireFile ()
 Attempts to map the entire file into memory. More...
 
virtual bool mapSectionOfFile (Range< int64 > samplesToMap)
 Attempts to map a section of the file into memory. More...
 
bool read (int *const *destSamples, int numDestChannels, int64 startSampleInSource, int numSamplesToRead, bool fillLeftoverChannelsWithCopies)
 Reads samples from the stream. More...
 
void read (AudioBuffer< float > *buffer, int startSampleInDestBuffer, int numSamples, int64 readerStartSample, bool useReaderLeftChan, bool useReaderRightChan)
 Fills a section of an AudioBuffer from this reader. More...
 
virtual void readMaxLevels (int64 startSample, int64 numSamples, Range< float > *results, int numChannelsToRead)
 Finds the highest and lowest sample levels from a section of the audio stream. More...
 
virtual void readMaxLevels (int64 startSample, int64 numSamples, float &lowestLeft, float &highestLeft, float &lowestRight, float &highestRight)
 Finds the highest and lowest sample levels from a section of the audio stream. More...
 
virtual bool readSamples (int **destSamples, int numDestChannels, int startOffsetInDestBuffer, int64 startSampleInFile, int numSamples)=0
 Subclasses must implement this method to perform the low-level read operation. More...
 
int64 searchForLevel (int64 startSample, int64 numSamplesToSearch, double magnitudeRangeMinimum, double magnitudeRangeMaximum, int minimumConsecutiveSamples)
 Scans the source looking for a sample whose magnitude is in a specified range. More...
 
void touchSample (int64 sample) const noexcept
 Touches the memory for the given sample, to force it to be loaded into active memory. More...
 

Public Attributes

unsigned int bitsPerSample = 0
 The number of bits per sample, e.g. More...
 
InputStreaminput
 The input stream, for use by subclasses. More...
 
int64 lengthInSamples = 0
 The total number of samples in the audio stream. More...
 
StringPairArray metadataValues
 A set of metadata values that the reader has pulled out of the stream. More...
 
unsigned int numChannels = 0
 The total number of channels in the audio stream. More...
 
double sampleRate = 0
 The sample-rate of the stream. More...
 
bool usesFloatingPointData = false
 Indicates whether the data is floating-point or fixed. More...
 

Protected Member Functions

 MemoryMappedAudioFormatReader (const File &file, const AudioFormatReader &details, int64 dataChunkStart, int64 dataChunkLength, int bytesPerFrame)
 Creates an MemoryMappedAudioFormatReader object. More...
 
int64 filePosToSample (int64 filePos) const noexcept
 Converts a byte position in the file to a sample index. More...
 
int64 sampleToFilePos (int64 sample) const noexcept
 Converts a sample index to a byte position in the file. More...
 
const void * sampleToPointer (int64 sample) const noexcept
 Converts a sample index to a pointer to the mapped file memory. More...
 
template<typename SampleType , typename Endianness >
Range< floatscanMinAndMaxInterleaved (int channel, int64 startSampleInFile, int64 numSamples) const noexcept
 Used by AudioFormatReader subclasses to scan for min/max ranges in interleaved data. More...
 

Static Protected Member Functions

static void clearSamplesBeyondAvailableLength (int **destSamples, int numDestChannels, int startOffsetInDestBuffer, int64 startSampleInFile, int &numSamples, int64 fileLengthInSamples)
 Used by AudioFormatReader subclasses to clear any parts of the data blocks that lie beyond the end of their available length. More...
 

Protected Attributes

int bytesPerFrame
 
int64 dataChunkStart
 
int64 dataLength
 
File file
 
std::unique_ptr< MemoryMappedFilemap
 
Range< int64mappedSection
 

Detailed Description

A specialised type of AudioFormatReader that uses a MemoryMappedFile to read directly from an audio file.

This allows for incredibly fast random-access to sample data in the mapped region of the file, but not all audio formats support it - see AudioFormat::createMemoryMappedReader().

Note that before reading samples from a MemoryMappedAudioFormatReader, you must first call mapEntireFile() or mapSectionOfFile() to ensure that the region you want to read has been mapped.

See also
AudioFormat::createMemoryMappedReader, AudioFormatReader

{Audio}

Constructor & Destructor Documentation

◆ MemoryMappedAudioFormatReader()

juce::MemoryMappedAudioFormatReader::MemoryMappedAudioFormatReader ( const File file,
const AudioFormatReader details,
int64  dataChunkStart,
int64  dataChunkLength,
int  bytesPerFrame 
)
protected

Creates an MemoryMappedAudioFormatReader object.

Note that before attempting to read any data, you must call mapEntireFile() or mapSectionOfFile() to ensure that the region you want to read has been mapped.

Member Function Documentation

◆ clearSamplesBeyondAvailableLength()

static void juce::AudioFormatReader::clearSamplesBeyondAvailableLength ( int **  destSamples,
int  numDestChannels,
int  startOffsetInDestBuffer,
int64  startSampleInFile,
int numSamples,
int64  fileLengthInSamples 
)
inlinestaticprotectedinherited

Used by AudioFormatReader subclasses to clear any parts of the data blocks that lie beyond the end of their available length.

References int(), jassert, and juce::zeromem().

◆ filePosToSample()

int64 juce::MemoryMappedAudioFormatReader::filePosToSample ( int64  filePos) const
inlineprotectednoexcept

Converts a byte position in the file to a sample index.

◆ getChannelLayout()

virtual AudioChannelSet juce::AudioFormatReader::getChannelLayout ( )
virtualinherited

Get the channel layout of the audio stream.

◆ getFile()

const File& juce::MemoryMappedAudioFormatReader::getFile ( ) const
inlinenoexcept

Returns the file that is being mapped.

◆ getFormatName()

const String& juce::AudioFormatReader::getFormatName ( ) const
inlinenoexceptinherited

Returns a description of what type of format this is.

E.g. "AIFF"

◆ getMappedSection()

Range<int64> juce::MemoryMappedAudioFormatReader::getMappedSection ( ) const
inlinenoexcept

Returns the sample range that's currently memory-mapped and available for reading.

◆ getNumBytesUsed()

size_t juce::MemoryMappedAudioFormatReader::getNumBytesUsed ( ) const
inline

Returns the number of bytes currently being mapped.

◆ getSample()

virtual void juce::MemoryMappedAudioFormatReader::getSample ( int64  sampleIndex,
float result 
) const
pure virtualnoexcept

Returns the samples for all channels at a given sample position.

The result array must be large enough to hold a value for each channel that this reader contains.

◆ mapEntireFile()

bool juce::MemoryMappedAudioFormatReader::mapEntireFile ( )

Attempts to map the entire file into memory.

◆ mapSectionOfFile()

virtual bool juce::MemoryMappedAudioFormatReader::mapSectionOfFile ( Range< int64 samplesToMap)
virtual

Attempts to map a section of the file into memory.

◆ read() [1/2]

bool juce::AudioFormatReader::read ( int *const *  destSamples,
int  numDestChannels,
int64  startSampleInSource,
int  numSamplesToRead,
bool  fillLeftoverChannelsWithCopies 
)
inherited

Reads samples from the stream.

Parameters
destSamplesan array of buffers into which the sample data for each channel will be written. If the format is fixed-point, each channel will be written as an array of 32-bit signed integers using the full range -0x80000000 to 0x7fffffff, regardless of the source's bit-depth. If it is a floating-point format, you should cast the resulting array to a (float**) to get the values (in the range -1.0 to 1.0 or beyond) If the format is stereo, then destSamples[0] is the left channel data, and destSamples[1] is the right channel. The numDestChannels parameter indicates how many pointers this array contains, but some of these pointers can be null if you don't want to read data for some of the channels
numDestChannelsthe number of array elements in the destChannels array
startSampleInSourcethe position in the audio file or stream at which the samples should be read, as a number of samples from the start of the stream. It's ok for this to be beyond the start or end of the available data - any samples that are out-of-range will be returned as zeros.
numSamplesToReadthe number of samples to read. If this is greater than the number of samples that the file or stream contains. the result will be padded with zeros
fillLeftoverChannelsWithCopiesif true, this indicates that if there's no source data available for some of the channels that you pass in, then they should be filled with copies of valid source channels. E.g. if you're reading a mono file and you pass 2 channels to this method, then if fillLeftoverChannelsWithCopies is true, both destination channels will be filled with the same data from the file's single channel. If fillLeftoverChannelsWithCopies was false, then only the first channel would be filled with the file's contents, and the second would be cleared. If there are many channels, e.g. you try to read 4 channels from a stereo file, then the last 3 would all end up with copies of the same data.
Returns
true if the operation succeeded, false if there was an error. Note that reading sections of data beyond the extent of the stream isn't an error - the reader should just return zeros for these regions
See also
readMaxLevels

◆ read() [2/2]

void juce::AudioFormatReader::read ( AudioBuffer< float > *  buffer,
int  startSampleInDestBuffer,
int  numSamples,
int64  readerStartSample,
bool  useReaderLeftChan,
bool  useReaderRightChan 
)
inherited

Fills a section of an AudioBuffer from this reader.

This will convert the reader's fixed- or floating-point data to the buffer's floating-point format, and will try to intelligently cope with mismatches between the number of channels in the reader and the buffer.

◆ readMaxLevels() [1/2]

virtual void juce::AudioFormatReader::readMaxLevels ( int64  startSample,
int64  numSamples,
Range< float > *  results,
int  numChannelsToRead 
)
virtualinherited

Finds the highest and lowest sample levels from a section of the audio stream.

This will read a block of samples from the stream, and measure the highest and lowest sample levels from the channels in that section, returning these as normalised floating-point levels.

Parameters
startSamplethe offset into the audio stream to start reading from. It's ok for this to be beyond the start or end of the stream.
numSampleshow many samples to read
resultsthis array will be filled with Range values for each channel. The array must contain numChannels elements.
numChannelsToReadthe number of channels of data to scan. This must be more than zero, but not more than the total number of channels that the reader contains
See also
read

Reimplemented in juce::AudioSubsectionReader.

◆ readMaxLevels() [2/2]

virtual void juce::AudioFormatReader::readMaxLevels ( int64  startSample,
int64  numSamples,
float lowestLeft,
float highestLeft,
float lowestRight,
float highestRight 
)
virtualinherited

Finds the highest and lowest sample levels from a section of the audio stream.

This will read a block of samples from the stream, and measure the highest and lowest sample levels from the channels in that section, returning these as normalised floating-point levels.

Parameters
startSamplethe offset into the audio stream to start reading from. It's ok for this to be beyond the start or end of the stream.
numSampleshow many samples to read
lowestLefton return, this is the lowest absolute sample from the left channel
highestLefton return, this is the highest absolute sample from the left channel
lowestRighton return, this is the lowest absolute sample from the right channel (if there is one)
highestRighton return, this is the highest absolute sample from the right channel (if there is one)
See also
read

◆ readSamples()

virtual bool juce::AudioFormatReader::readSamples ( int **  destSamples,
int  numDestChannels,
int  startOffsetInDestBuffer,
int64  startSampleInFile,
int  numSamples 
)
pure virtualinherited

Subclasses must implement this method to perform the low-level read operation.

Callers should use read() instead of calling this directly.

Parameters
destSamplesthe array of destination buffers to fill. Some of these pointers may be null
numDestChannelsthe number of items in the destSamples array. This value is guaranteed not to be greater than the number of channels that this reader object contains
startOffsetInDestBufferthe number of samples from the start of the dest data at which to begin writing
startSampleInFilethe number of samples into the source data at which to begin reading. This value is guaranteed to be >= 0.
numSamplesthe number of samples to read

Implemented in juce::AudioCDReader, juce::AudioSubsectionReader, and juce::BufferingAudioReader.

◆ sampleToFilePos()

int64 juce::MemoryMappedAudioFormatReader::sampleToFilePos ( int64  sample) const
inlineprotectednoexcept

Converts a sample index to a byte position in the file.

◆ sampleToPointer()

const void* juce::MemoryMappedAudioFormatReader::sampleToPointer ( int64  sample) const
inlineprotectednoexcept

Converts a sample index to a pointer to the mapped file memory.

References juce::addBytesToPointer().

◆ scanMinAndMaxInterleaved()

template<typename SampleType , typename Endianness >
Range<float> juce::MemoryMappedAudioFormatReader::scanMinAndMaxInterleaved ( int  channel,
int64  startSampleInFile,
int64  numSamples 
) const
inlineprotectednoexcept

◆ searchForLevel()

int64 juce::AudioFormatReader::searchForLevel ( int64  startSample,
int64  numSamplesToSearch,
double  magnitudeRangeMinimum,
double  magnitudeRangeMaximum,
int  minimumConsecutiveSamples 
)
inherited

Scans the source looking for a sample whose magnitude is in a specified range.

This will read from the source, either forwards or backwards between two sample positions, until it finds a sample whose magnitude lies between two specified levels.

If it finds a suitable sample, it returns its position; if not, it will return -1.

There's also a minimumConsecutiveSamples setting to help avoid spikes or zero-crossing points when you're searching for a continuous range of samples

Parameters
startSamplethe first sample to look at
numSamplesToSearchthe number of samples to scan. If this value is negative, the search will go backwards
magnitudeRangeMinimumthe lowest magnitude (inclusive) that is considered a hit, from 0 to 1.0
magnitudeRangeMaximumthe highest magnitude (inclusive) that is considered a hit, from 0 to 1.0
minimumConsecutiveSamplesif this is > 0, the method will only look for a sequence of this many consecutive samples, all of which lie within the target range. When it finds such a sequence, it returns the position of the first in-range sample it found (i.e. the earliest one if scanning forwards, the latest one if scanning backwards)

◆ touchSample()

void juce::MemoryMappedAudioFormatReader::touchSample ( int64  sample) const
noexcept

Touches the memory for the given sample, to force it to be loaded into active memory.

Member Data Documentation

◆ bitsPerSample

unsigned int juce::AudioFormatReader::bitsPerSample = 0
inherited

The number of bits per sample, e.g.

16, 24, 32.

◆ bytesPerFrame

int juce::MemoryMappedAudioFormatReader::bytesPerFrame
protected

◆ dataChunkStart

int64 juce::MemoryMappedAudioFormatReader::dataChunkStart
protected

◆ dataLength

int64 juce::MemoryMappedAudioFormatReader::dataLength
protected

◆ file

File juce::MemoryMappedAudioFormatReader::file
protected

◆ input

InputStream* juce::AudioFormatReader::input
inherited

The input stream, for use by subclasses.

◆ lengthInSamples

int64 juce::AudioFormatReader::lengthInSamples = 0
inherited

The total number of samples in the audio stream.

◆ map

std::unique_ptr<MemoryMappedFile> juce::MemoryMappedAudioFormatReader::map
protected

◆ mappedSection

Range<int64> juce::MemoryMappedAudioFormatReader::mappedSection
protected

◆ metadataValues

StringPairArray juce::AudioFormatReader::metadataValues
inherited

A set of metadata values that the reader has pulled out of the stream.

Exactly what these values are depends on the format, so you can check out the format implementation code to see what kind of stuff they understand.

◆ numChannels

unsigned int juce::AudioFormatReader::numChannels = 0
inherited

The total number of channels in the audio stream.

◆ sampleRate

double juce::AudioFormatReader::sampleRate = 0
inherited

The sample-rate of the stream.

◆ usesFloatingPointData

bool juce::AudioFormatReader::usesFloatingPointData = false
inherited

Indicates whether the data is floating-point or fixed.


The documentation for this class was generated from the following file: