mp4box/src/parsing/dfLa.js

JavaScript version of GPAC's MP4Box tool

BoxParser.createFullBoxCtor("dfLa", "FLACSpecificBox", function(stream) {
    var BLOCKTYPE_MASK = 0x7F;
    var LASTMETADATABLOCKFLAG_MASK = 0x80;

    var boxesFound = [];
    var knownBlockTypes = [
        "STREAMINFO",
        "PADDING",
        "APPLICATION",
        "SEEKTABLE",
        "VORBIS_COMMENT",
        "CUESHEET",
        "PICTURE",
        "RESERVED"
    ];

    // for (i=0; ; i++) { // to end of box
    do {
        var flagAndType = stream.readUint8();

        var type = Math.min(
            (flagAndType & BLOCKTYPE_MASK),
            (knownBlockTypes.length - 1)
        );

        // if this is a STREAMINFO block, read the true samplerate since this
        // can be different to the AudioSampleEntry samplerate.
        if (!(type)) {
            // read past all the other stuff
            stream.readUint8Array(13);

            // extract samplerate
            this.samplerate = (stream.readUint32() >> 12);

            // read to end of STREAMINFO
            stream.readUint8Array(20);
        } else {
            // not interested in other block types so just discard length bytes
            stream.readUint8Array(stream.readUint24());
        }

        boxesFound.push(knownBlockTypes[type]);

        if (!!(flagAndType & LASTMETADATABLOCKFLAG_MASK)) {
            break;
        }
    } while (true);

    this.numMetadataBlocks =
        boxesFound.length + " (" + boxesFound.join(", ") + ")";
});