Function

AudioFileReadPackets

Reads a fixed duration of audio data from an audio file.

Declaration

OSStatus AudioFileReadPackets(AudioFileID inAudioFile, Boolean inUseCache, UInt32 *outNumBytes, AudioStreamPacketDescription *outPacketDescriptions, SInt64 inStartingPacket, UInt32 *ioNumPackets, void *outBuffer);

Parameters

inAudioFile

The audio file whose audio packets you want to read.

inUseCache

Set to true to cache the data. Otherwise, set to false.

outNumBytes

On output, the number of bytes actually read.

outPacketDescriptions

On output, an array of packet descriptions for the packets that were read. The array that you pass must be large enough to accommodate descriptions for the number of packets requested in the ioNumPackets parameter.

This parameter applies only to variable bit-rate data. If the file being read contains constant bit-rate (CBR) data, such as linear PCM, this parameter does not get filled. Pass NULL if the file’s data format is CBR.

inStartingPacket

The packet index of the first packet you want to read.

ioNumPackets

On input, the number of packets to read. On output, the number of packets actually read.

You will see a difference in the input and output values when this function has reached the end of the file you are reading. In this case, the output value for this parameter is smaller than its input value.

outBuffer

Memory that you allocate to hold the read packets. Determine an appropriate size by multiplying the number of packets requested (in the ioNumPackets parameter) by the maximum (or upper bound for) packet size of the audio file. For uncompressed audio formats, a packet is equal to a frame.

Return Value

A result code. See Result Codes.

Discussion

If you do not need to read a fixed duration of audio data, but rather want to use your memory buffer most efficiently, use AudioFileReadPacketData instead of this function.

When reading variable bit-rate (VBR) audio data, using this function requires that you allocate more memory than you would for the AudioFileReadPacketData function. See the descriptions for the outBuffer parameter in each of these two functions.

In addition, this function is less efficient than AudioFileReadPacketData when reading compressed file formats that do not have packet tables, such as MP3 or ADTS. Use this function only when you need to read a fixed duration of audio data, or when you are reading only uncompressed audio.

Audio File Services reads one 32-bit chunk of a file at a time.

See Also

Reading and Writing Audio Files

AudioFileReadBytes

Reads bytes of audio data from an audio file.

AudioFileWriteBytes

Writes bytes of audio data to an audio file.

AudioFileReadPacketData

Reads packets of audio data from an audio file.

AudioFileWritePackets

Writes packets of audio data to an audio data file.