extractH264NalUnits()

fl::vector< fl::u8 > fl::extractH264NalUnits	(	fl::span< const fl::u8 >	data,
		const Mp4TrackInfo &	track,
		fl::string *	error )

Definition at line 283 of file mp4_parser.cpp.hpp.

                                                         {
    fl::vector<fl::u8> annexB;
 
    if (!track.isValid) {
        if (error) *error = "Invalid track info";
        return annexB;
    }
 
    fl::u8 nalLenSize = track.lengthSizeMinusOne + 1; // typically 4
 
    // Emit SPS NAL units with Annex B start codes
    for (const auto& sps : track.sps) {
        annexB.push_back(0x00);
        annexB.push_back(0x00);
        annexB.push_back(0x00);
        annexB.push_back(0x01);
        for (fl::size j = 0; j < sps.size(); j++) {
            annexB.push_back(sps[j]);
        }
    }
 
    // Emit PPS NAL units
    for (const auto& pps : track.pps) {
        annexB.push_back(0x00);
        annexB.push_back(0x00);
        annexB.push_back(0x00);
        annexB.push_back(0x01);
        for (fl::size j = 0; j < pps.size(); j++) {
            annexB.push_back(pps[j]);
        }
    }
 
    // Find mdat box and convert AVCC NAL units to Annex B
    fl::size mdatPos = fl::size(-1);
    {
        fl::size pos = 0;
        while (pos + 8 <= data.size()) {
            bool ok = true;
            fl::u32 boxSize = readU32BE(data, pos, ok);
            if (!ok || boxSize < 8) break;
            if (boxIs(data, pos + 4, "mdat")) {
                mdatPos = pos;
                break;
            }
            pos += boxSize;
        }
    }
 
    if (mdatPos == fl::size(-1)) {
        if (error) *error = "No mdat box found";
        return annexB;
    }
 
    bool ok = true;
    fl::u32 mdatSize = readU32BE(data, mdatPos, ok);
    if (!ok) {
        if (error) *error = "Invalid mdat box size";
        return annexB;
    }
 
    fl::size mdatBody = mdatPos + 8;
    fl::size mdatEnd = mdatPos + mdatSize;
    if (mdatEnd > data.size()) mdatEnd = data.size();
 
    fl::size pos = mdatBody;
    while (pos + nalLenSize <= mdatEnd) {
        fl::u32 nalLen = 0;
        for (fl::u8 k = 0; k < nalLenSize; k++) {
            nalLen = (nalLen << 8) | data[pos + k];
        }
        pos += nalLenSize;
 
        if (pos + nalLen > mdatEnd) break;
 
        // Emit Annex B start code + NAL data
        annexB.push_back(0x00);
        annexB.push_back(0x00);
        annexB.push_back(0x00);
        annexB.push_back(0x01);
        for (fl::u32 j = 0; j < nalLen; j++) {
            annexB.push_back(data[pos + j]);
        }
        pos += nalLen;
    }
 
    return annexB;
}

References fl::Mp4TrackInfo::isValid, fl::Mp4TrackInfo::lengthSizeMinusOne, pos, fl::Mp4TrackInfo::pps, fl::vector< T >::push_back(), fl::span< T, Extent >::size(), and fl::Mp4TrackInfo::sps.

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