Question

Is there any comprehensive documentation/tutorial for this function (for iOS core audio) CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer? Couldn’t find anything on the web, and the examples on stack over flow leave much to be desired.

Answer 1

after months of working with CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer, i’ve learned that while it’s hard to find a post or link specifically about the said function, it’s also easy to find a ton of resources about the general topic of audio in iOS, chief amongst them is the book Learning Core Audio..

it takes time for the dense concepts of iOS core audio to sink in and it takes a lot of practice.. once things sink in.. the above method will become an easy tool in a much bigger tool box.. and all its parameters and uses will make intuitive sense

also a quick way to find out about the parameters and what the function does above exactly.. simply go to the documentation provided in the header file (ie in XCode, highlight the method and right click-> Jump to Definition).. you’ll see this in CMSampleBuffer.h (but again if you’re new to core audio.. don’t get frustrated if you look at all these parameters and understand only 10% of it.. it happened to all of us and it takes time):

/*!
    @function   CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer
    @abstract   Creates an AudioBufferList containing the data from the CMSampleBuffer,
                and a CMBlockBuffer which references (and manages the lifetime of) the
                data in that AudioBufferList.  The data may or may not be copied,
                depending on the contiguity and 16-byte alignment of the CMSampleBuffer's
                data. The buffers placed in the AudioBufferList are guaranteed to be contiguous.
                The buffers in the AudioBufferList will be 16-byte-aligned if
                kCMSampleBufferFlag_AudioBufferList_Assure16ByteAlignment is passed in.
*/
CM_EXPORT
OSStatus CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer(
    CMSampleBufferRef sbuf,             /*! @param sbuf
                                        CMSampleBuffer being accessed. */
    size_t *bufferListSizeNeededOut,    /*! @param bufferListSizeNeededOut
                                        Receives the size of the AudioBufferList required to
                                        accommodate the data. May be NULL. */
    AudioBufferList *bufferListOut,     /*! @param bufferListOut
                                        Allocated by the caller, sized as specified by bufferListSizeNeededOut.
                                        It is filled in with pointers into the retained blockBufferOut.
                                        May be NULL. */
    size_t bufferListSize,              /*! @param bufferListSize
                                        Size of the bufferListOut allocated by the client. If bufferListOut
                                        is not NULL and bufferListSize is insufficient, kFigSampleBufferError_ArrayTooSmall
                                        is returned. */ 
    CFAllocatorRef bbufStructAllocator, /*! @param bbufStructAllocator
                                        Allocator to use when creating the CMBlockBuffer structure. */
    CFAllocatorRef bbufMemoryAllocator, /*! @param bbufMemoryAllocator
                                        Allocator to use for memory block held by the CMBlockBuffer. */
    uint32_t flags,                     /*! @param flags
                                        Flags controlling operation. */
    CMBlockBufferRef *blockBufferOut)   /*! @param blockBufferOut
                                        The retained CMBlockBuffer. */
                            __OSX_AVAILABLE_STARTING(__MAC_10_7,__IPHONE_4_0);