New control block for AudioTrack and AudioRecord

{

public:

    // FIXME merge with AudioTrackShared::Buffer, AudioTrack::Buffer, and AudioRecord::Buffer

    //       and rename getNextBuffer() to obtainBuffer()

    struct Buffer {

        Buffer() : raw(NULL), frameCount(0) { }

        union {

    // pts is the local time when the next sample yielded by getNextBuffer

    // will be rendered.

    // Pass kInvalidPTS if the PTS is unknown or not applicable.

    // On entry:

    //  buffer              != NULL

    //  buffer->raw         unused

    //  buffer->frameCount  maximum number of desired frames

    // On successful return:

    //  status              NO_ERROR

    //  buffer->raw         non-NULL pointer to buffer->frameCount contiguous available frames

    //  buffer->frameCount  number of contiguous available frames at buffer->raw,

    //                      0 < buffer->frameCount <= entry value

    // On error return:

    //  status              != NO_ERROR

    //  buffer->raw         NULL

    //  buffer->frameCount  0

    virtual status_t getNextBuffer(Buffer* buffer, int64_t pts = kInvalidPTS) = 0;

    virtual void releaseBuffer(Buffer* buffer) = 0;