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/**
 * Decodes an audio frame from \p buf into \p samples.
 * The avcodec_decode_audio2() function decodes an audio frame from the input
 * buffer \p buf of size \p buf_size. To decode it, it makes use of the
 * audio codec which was coupled with \p avctx using avcodec_open(). The
 * resulting decoded frame is stored in output buffer \p samples.  If no frame
 * could be decompressed, \p frame_size_ptr is zero. Otherwise, it is the
 * decompressed frame size in \e bytes.
 *
 * @warning You \e must set \p frame_size_ptr to the allocated size of the
 * output buffer before calling avcodec_decode_audio2().
 *
 * @warning The input buffer must be \c FF_INPUT_BUFFER_PADDING_SIZE larger than
 * the actual read bytes because some optimized bitstream readers read 32 or 64
 * bits at once and could read over the end.
 *
 * @warning The end of the input buffer \p buf should be set to 0 to ensure that
 * no overreading happens for damaged MPEG streams.
 *
 * @note You might have to align the input buffer \p buf and output buffer \p
 * samples. The alignment requirements depend on the CPU: On some CPUs it isn't
 * necessary at all, on others it won't work at all if not aligned and on others
 * it will work but it will have an impact on performance. In practice, the
 * bitstream should have 4 byte alignment at minimum and all sample data should
 * be 16 byte aligned unless the CPU doesn't need it (AltiVec and SSE do). If
 * the linesize is not a multiple of 16 then there's no sense in aligning the
 * start of the buffer to 16.
 *
 * @param avctx the codec context
 * @param[out] samples the output buffer
 * @param[in,out] frame_size_ptr the output buffer size in bytes
 * @param[in] buf the input buffer
 * @param[in] buf_size the input buffer size in bytes
 * @return On error a negative value is returned, otherwise the number of bytes
 * used or zero if no frame could be decompressed.
 */
int avcodec_decode_audio2(AVCodecContext *avctx, int16_t *samples,
                         int *frame_size_ptr,
                         uint8_t *buf, int buf_size);