UnpackFrameHeader()

int fl::third_party::UnpackFrameHeader	(	MP3DecInfo *	mp3DecInfo,
		const unsigned char *	buf )

Definition at line 223 of file bitstream.hpp.

{
 
    int verIdx;
    FrameHeader *fh;
 
    /* validate pointers and sync word */
    if (!mp3DecInfo || !mp3DecInfo->FrameHeaderPS || (buf[0] & SYNCWORDH) != SYNCWORDH || (buf[1] & SYNCWORDL) != SYNCWORDL)
        return -1;
 
    fh = ((FrameHeader *)(mp3DecInfo->FrameHeaderPS));
 
    /* read header fields - use bitmasks instead of GetBits() for speed, since format never varies */
    verIdx =         (buf[1] >> 3) & 0x03;
    fh->ver =        (MPEGVersion)( verIdx == 0 ? MPEG25 : ((verIdx & 0x01) ? MPEG1 : MPEG2) );
    fh->layer = 4 - ((buf[1] >> 1) & 0x03);     /* easy mapping of index to layer number, 4 = error */
    fh->crc =   1 - ((buf[1] >> 0) & 0x01);
    fh->brIdx =      (buf[2] >> 4) & 0x0f;
    fh->srIdx =      (buf[2] >> 2) & 0x03;
    fh->paddingBit = (buf[2] >> 1) & 0x01;
    fh->privateBit = (buf[2] >> 0) & 0x01;
    fh->sMode =      (StereoMode)((buf[3] >> 6) & 0x03);      /* maps to correct enum (see definition) */    
    fh->modeExt =    (buf[3] >> 4) & 0x03;
    fh->copyFlag =   (buf[3] >> 3) & 0x01;
    fh->origFlag =   (buf[3] >> 2) & 0x01;
    fh->emphasis =   (buf[3] >> 0) & 0x03;
 
    /* check parameters to avoid indexing tables with bad values */
    if (fh->srIdx == 3 || fh->layer == 4 || fh->brIdx == 15)
        return -1;
 
    fh->sfBand = &sfBandTable[fh->ver][fh->srIdx]; /* for readability (we reference sfBandTable many times in decoder) */
    if (fh->sMode != Joint)       /* just to be safe (dequant, stproc check fh->modeExt) */
        fh->modeExt = 0;
 
    /* init user-accessible data */
    mp3DecInfo->nChans = (fh->sMode == Mono ? 1 : 2);
    mp3DecInfo->samprate = samplerateTab[fh->ver][fh->srIdx];
    mp3DecInfo->nGrans = (fh->ver == MPEG1 ? NGRANS_MPEG1 : NGRANS_MPEG2);
    mp3DecInfo->nGranSamps = ((int)samplesPerFrameTab[fh->ver][fh->layer - 1]) / mp3DecInfo->nGrans;
    mp3DecInfo->layer = fh->layer;
    mp3DecInfo->version = fh->ver;
    
    /* get bitrate and nSlots from table, unless brIdx == 0 (free mode) in which case caller must figure it out himself
     * question - do we want to overwrite mp3DecInfo->bitrate with 0 each time if it's free mode, and
     *  copy the pre-calculated actual free bitrate into it in mp3dec.c (according to the spec, 
     *  this shouldn't be necessary, since it should be either all frames free or none free)
     */
    if (fh->brIdx) {
        mp3DecInfo->bitrate = ((int)bitrateTab[fh->ver][fh->layer - 1][fh->brIdx]) * 1000;
    
        /* nSlots = total frame bytes (from table) - sideInfo bytes - header - CRC (if present) + pad (if present) */
        mp3DecInfo->nSlots = (int)slotTab[fh->ver][fh->srIdx][fh->brIdx] - 
            (int)sideBytesTab[fh->ver][(fh->sMode == Mono ? 0 : 1)] - 
            4 - (fh->crc ? 2 : 0) + (fh->paddingBit ? 1 : 0);
    }
 
    /* load crc word, if enabled, and return length of frame header (in bytes) */
    if (fh->crc) {
        fh->CRCWord = ((int)buf[4] << 8 | (int)buf[5] << 0);
        return 6;
    } else {
        fh->CRCWord = 0;
        return 4;
    }
}

References bitrateTab, fl::third_party::_FrameHeader::brIdx, fl::third_party::_FrameHeader::copyFlag, fl::third_party::_FrameHeader::crc, fl::third_party::_FrameHeader::CRCWord, fl::third_party::_FrameHeader::emphasis, FL_NOEXCEPT, Joint, fl::third_party::_FrameHeader::layer, fl::third_party::_FrameHeader::modeExt, Mono, MPEG1, MPEG2, MPEG25, NGRANS_MPEG1, NGRANS_MPEG2, fl::third_party::_FrameHeader::origFlag, fl::third_party::_FrameHeader::paddingBit, fl::third_party::_FrameHeader::privateBit, samplerateTab, samplesPerFrameTab, fl::third_party::_FrameHeader::sfBand, sfBandTable, sideBytesTab, slotTab, fl::third_party::_FrameHeader::sMode, fl::third_party::_FrameHeader::srIdx, SYNCWORDH, SYNCWORDL, and fl::third_party::_FrameHeader::ver.

Referenced by MP3Decode(), and MP3GetNextFrameInfo().

Here is the caller graph for this function: