mp3dec.c

著名的 helix realplayer 基于手机 symbian 系统的 播放器全套源代码

/**************************************************************************************
 * Function:    MP3GetNextFrameInfo
 *
 * Description: parse MP3 frame header
 *
 * Inputs:      valid MP3 decoder instance pointer (HMP3Decoder)
 *              pointer to MP3FrameInfo struct
 *              pointer to buffer containing valid MP3 frame header (located using 
 *                MP3FindSyncWord(), above)
 *
 * Outputs:     filled-in MP3FrameInfo struct
 *
 * Return:      error code, defined in mp3dec.h (0 means no error, < 0 means error)
 **************************************************************************************/
int MP3GetNextFrameInfo(HMP3Decoder hMP3Decoder, MP3FrameInfo *mp3FrameInfo, unsigned char *buf)
{
	MP3DecInfo *mp3DecInfo = (MP3DecInfo *)hMP3Decoder;

	if (!mp3DecInfo)
		return ERR_MP3_NULL_POINTER;

	if (UnpackFrameHeader(mp3DecInfo, buf) == -1 || mp3DecInfo->layer != 3)
		return ERR_MP3_INVALID_FRAMEHEADER;

	MP3GetLastFrameInfo(mp3DecInfo, mp3FrameInfo);

	return ERR_MP3_NONE;
}

/**************************************************************************************
 * Function:    MP3ClearBadFrame
 *
 * Description: zero out pcm buffer if error decoding MP3 frame
 *
 * Inputs:      mp3DecInfo struct with correct frame size parameters filled in
 *              pointer pcm output buffer
 *
 * Outputs:     zeroed out pcm buffer
 *
 * Return:      none
 **************************************************************************************/
static void MP3ClearBadFrame(MP3DecInfo *mp3DecInfo, short *outbuf)
{
	int i;

	if (!mp3DecInfo)
		return;

	for (i = 0; i < mp3DecInfo->nGrans * mp3DecInfo->nGranSamps * mp3DecInfo->nChans; i++)
		outbuf[i] = 0;
}

/**************************************************************************************
 * Function:    MP3Decode
 *
 * Description: decode one frame of MP3 data
 *
 * Inputs:      valid MP3 decoder instance pointer (HMP3Decoder)
 *              double pointer to buffer of MP3 data (containing headers + mainData)
 *              number of valid bytes remaining in inbuf
 *              pointer to outbuf, big enough to hold one frame of decoded PCM samples
 *              flag indicating whether MP3 data is normal MPEG format (useSize = 0)
 *                or reformatted as "self-contained" frames (useSize = 1)
 *
 * Outputs:     PCM data in outbuf, interleaved LRLRLR... if stereo
 *                number of output samples = nGrans * nGranSamps * nChans
 *              updated inbuf pointer, updated bytesLeft
 *
 * Return:      error code, defined in mp3dec.h (0 means no error, < 0 means error)
 *
 * Notes:       switching useSize on and off between frames in the same stream 
 *                is not supported (bit reservoir is not maintained if useSize on)
 **************************************************************************************/
int MP3Decode(HMP3Decoder hMP3Decoder, unsigned char **inbuf, int *bytesLeft, short *outbuf, int useSize)
{
	int offset, bitOffset, mainBits, gr, ch, fhBytes, siBytes, freeFrameBytes;
	int prevBitOffset, sfBlockBits, huffBlockBits;
	unsigned char *mainPtr;
	MP3DecInfo *mp3DecInfo = (MP3DecInfo *)hMP3Decoder;

	if (!mp3DecInfo)
		return ERR_MP3_NULL_POINTER;

	/* unpack frame header */
	fhBytes = UnpackFrameHeader(mp3DecInfo, *inbuf);
	if (fhBytes < 0)
		return ERR_MP3_INVALID_FRAMEHEADER;		/* don't clear outbuf since we don't know size (failed to parse header) */
	*inbuf += fhBytes;
	
	/* unpack side info */
	siBytes = UnpackSideInfo(mp3DecInfo, *inbuf);
	if (siBytes < 0) {
		MP3ClearBadFrame(mp3DecInfo, outbuf);
		return ERR_MP3_INVALID_SIDEINFO;
	}
	*inbuf += siBytes;
	*bytesLeft -= (fhBytes + siBytes);
	
	/* if free mode, need to calculate bitrate and nSlots manually, based on frame size */
	if (mp3DecInfo->bitrate == 0 || mp3DecInfo->freeBitrateFlag) {
		if (!mp3DecInfo->freeBitrateFlag) {
			/* first time through, need to scan for next sync word and figure out frame size */
			mp3DecInfo->freeBitrateFlag = 1;
			mp3DecInfo->freeBitrateSlots = MP3FindFreeSync(*inbuf, *inbuf - fhBytes - siBytes, *bytesLeft);
			if (mp3DecInfo->freeBitrateSlots < 0) {
				MP3ClearBadFrame(mp3DecInfo, outbuf);
				return ERR_MP3_FREE_BITRATE_SYNC;
			}
			freeFrameBytes = mp3DecInfo->freeBitrateSlots + fhBytes + siBytes;
			mp3DecInfo->bitrate = (freeFrameBytes * mp3DecInfo->samprate * 8) / (mp3DecInfo->nGrans * mp3DecInfo->nGranSamps);
		}
		mp3DecInfo->nSlots = mp3DecInfo->freeBitrateSlots + CheckPadBit(mp3DecInfo);	/* add pad byte, if required */
	}

	/* useSize != 0 means we're getting reformatted (RTP) packets (see RFC 3119)
	 *  - calling function assembles "self-contained" MP3 frames by shifting any main_data 
	 *      from the bit reservoir (in previous frames) to AFTER the sync word and side info
	 *  - calling function should set mainDataBegin to 0, and tell us exactly how large this
	 *      frame is (in bytesLeft)
	 */
	if (useSize) {
		mp3DecInfo->nSlots = *bytesLeft;
		if (mp3DecInfo->mainDataBegin != 0 || mp3DecInfo->nSlots <= 0) {
			/* error - non self-contained frame, or missing frame (size <= 0), could do loss concealment here */
			MP3ClearBadFrame(mp3DecInfo, outbuf);
			return ERR_MP3_INVALID_FRAMEHEADER;
		}

		/* can operate in-place on reformatted frames */
		mp3DecInfo->mainDataBytes = mp3DecInfo->nSlots;
		mainPtr = *inbuf;
		*inbuf += mp3DecInfo->nSlots;
		*bytesLeft -= (mp3DecInfo->nSlots);
	} else {
		/* out of data - assume last or truncated frame */
		if (mp3DecInfo->nSlots > *bytesLeft)
			return ERR_MP3_INDATA_UNDERFLOW;	

		/* fill main data buffer with enough new data for this frame */
		if (mp3DecInfo->mainDataBytes >= mp3DecInfo->mainDataBegin) {
			/* adequate "old" main data available (i.e. bit reservoir) */
			memmove(mp3DecInfo->mainBuf, mp3DecInfo->mainBuf + mp3DecInfo->mainDataBytes - mp3DecInfo->mainDataBegin, mp3DecInfo->mainDataBegin);
			memcpy(mp3DecInfo->mainBuf + mp3DecInfo->mainDataBegin, *inbuf, mp3DecInfo->nSlots);

			mp3DecInfo->mainDataBytes = mp3DecInfo->mainDataBegin + mp3DecInfo->nSlots;
			*inbuf += mp3DecInfo->nSlots;
			*bytesLeft -= (mp3DecInfo->nSlots);
			mainPtr = mp3DecInfo->mainBuf;
		} else {
			/* not enough data in bit reservoir from previous frames (perhaps starting in middle of file) */
			memcpy(mp3DecInfo->mainBuf + mp3DecInfo->mainDataBytes, *inbuf, mp3DecInfo->nSlots);
			mp3DecInfo->mainDataBytes += mp3DecInfo->nSlots;
			*inbuf += mp3DecInfo->nSlots;
			*bytesLeft -= (mp3DecInfo->nSlots);

			return ERR_MP3_MAINDATA_UNDERFLOW;
		}
	}
	bitOffset = 0;
	mainBits = mp3DecInfo->mainDataBytes * 8;

	/* decode one complete frame */
	for (gr = 0; gr < mp3DecInfo->nGrans; gr++) {
		for (ch = 0; ch < mp3DecInfo->nChans; ch++) {
			/* unpack scale factors and compute size of scale factor block */
			prevBitOffset = bitOffset;
			offset = UnpackScaleFactors(mp3DecInfo, mainPtr, &bitOffset, mainBits, gr, ch);

			sfBlockBits = 8*offset - prevBitOffset + bitOffset;
			huffBlockBits = mp3DecInfo->part23Length[gr][ch] - sfBlockBits;
			mainPtr += offset;
			mainBits -= sfBlockBits;

			if (offset < 0 || mainBits < huffBlockBits) {
				MP3ClearBadFrame(mp3DecInfo, outbuf);
				return ERR_MP3_INVALID_SCALEFACT;
			}

			/* decode Huffman code words */
			prevBitOffset = bitOffset;
			offset = DecodeHuffman(mp3DecInfo, mainPtr, &bitOffset, huffBlockBits, gr, ch);
			if (offset < 0) {
				MP3ClearBadFrame(mp3DecInfo, outbuf);
				return ERR_MP3_INVALID_HUFFCODES;
			}

			mainPtr += offset;
			mainBits -= (8*offset - prevBitOffset + bitOffset);
		}
		/* dequantize coefficients, decode stereo, reorder short blocks */
		Dequantize(mp3DecInfo, gr);

		/* alias reduction, inverse MDCT, overlap-add, frequency inversion */
		for (ch = 0; ch < mp3DecInfo->nChans; ch++)
			IMDCT(mp3DecInfo, gr, ch);

		/* subband transform - if stereo, interleaves pcm LRLRLR */
		Subband(mp3DecInfo, outbuf + gr*mp3DecInfo->nGranSamps*mp3DecInfo->nChans);
	}

	return ERR_MP3_NONE;
}