/**
 * Decode a Data packet.
 * Return a negative value on error, otherwise return the number of bytes used.
 * If no data was decompressed then size parameter of output is zero.
 * In Output AVBuffer format of data is based on the codec used, to use the 
 * data directly from output buffer one might need to use header file of
 * codec used as interface. This output buffer can be directly given to
 * avcodec_encode_data api if encoder support that decoder output.
 * 
 * @param avctx the codec context
 * @param[out] output The Preallocated AVBuffer in which the decoded data will
 *                    be stored, must be freed with free parameter of  AVBuffer
 *                    if size is not 0.
 * @param[in] avpkt The input AVPacket containing the input buffer.
 */