Inside Macintosh: QuickTime Reference

ExtendedSoundParamBlock

The ExtendedSoundParamBlock is an extended form of SoundParamBlock. Like ExtendedSoundComponentData, it consists of the unextended classic structure followed by new fields.

struct ExtendedSoundParamBlock { SoundParamBlock pb; /*classic SoundParamBlock except recordSize == sizeof(ExtendedSoundParamBlock)*/ short reserved; long extendedFlags; /*flags*/ long bufferSize; /*size of buffer in bytes*/ }; typedef struct ExtendedSoundParamBlock ExtendedSoundParamBlock; typedef ExtendedSoundParamBlock * ExtendedSoundParamBlockPtr;

Unlike SoundComponentData, however, the recordSize field of the SoundParamBlock is used to detect if this is an ExtendedSoundParamBlock.

If the record size is greater than SoundParamBlock, then you know it has been extended. Also, in the future, it is expected that this structure will grow, so you want to check for a record of sufficient size to hold the fields you are seeking.

The fields of ExtendedSoundParamBlock are:

pb: Classic SoundParamBlock record. Its recordSize field allows you to detect extended records.
reserved: Reserved.
extendedFlags: Same interpretation as extendedFlags in ExtendedSoundComponentData.
bufferSize: Size of buffer in bytes. Only valid if extendedFlags field has the kExtendedSoundBufferSizeValid flag set.

Since the embedded SoundParamBlock contains a SoundComponentData, the kExtendedSoundSampleCountNotValid flag set refers to the sampleCount field of that record. Be aware that the embedded SoundComponentData's flags field should never have its kExtendedSoundData flag set. This would mislead a client passed only a pointer to the SoundComponentData to misinterpet it as an extended record.

An ExtendedSoundParamBlock can be passed to the sound component's SoundComponentPlaySourceBuffer routine. Also, the moreRtn of the SoundParamBlock may return a reference to an ExtendedSoundParamBlock.

In both cases, check that the record is extended before interpreting the extended fields.

Inside Macintosh: QuickTime Reference