88 lines
2.1 KiB
JavaScript
88 lines
2.1 KiB
JavaScript
DataView.prototype.getString = function(offset, length) {
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text = '';
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let end = offset + length;
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for (let i = offset; i < end; i++) {
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text += String.fromCharCode(this.getUint8(i));
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}
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return text;
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}
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class MP4Tree {
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constructor(data) {
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this.data = new DataView(data);
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this.codecs = [];
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this.idx = 0;
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this.parse_codecs();
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}
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parse_codecs() {
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this.parse_into('moov', 8);
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while (this.idx < this.data.byteLength) {
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if (!this.parse_until('trak')) {
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break;
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}
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const curr_track_end = this.idx + this.read_next_head().len;
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this.idx += 8
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this.parse_into('mdia', 8);
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this.parse_into('minf', 8);
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const track_type_head = this.read_next_head().name;
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if (track_type_head == 'smhd' || track_type_head == 'vmhd') {
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this.parse_into('stbl', 8);
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this.parse_into('stsd', 16);
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const media_sample = this.read_next_head().name;
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if (media_sample == 'avc1') {
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this.parse_avc1();
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} else if (media_sample == 'mp4a') {
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this.parse_mp4a();
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}
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}
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this.idx = curr_track_end;
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}
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}
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parse_avc1() {
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this.parse_into('avc1', 86);
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this.parse_into('avcC', 8);
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const avc_profile = (this.data.getUint32(this.idx) & 0xffffff).toString(16);
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this.codecs.push('avc1.' + avc_profile);
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}
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parse_mp4a() {
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this.parse_into('mp4a', 36);
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this.parse_into('esds', 12);
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const oti = this.data.getUint8(this.idx + 13).toString(16);
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const aot = (this.data.getUint8(this.idx + 31) >> 3).toString(10);
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this.codecs.push(["mp4a", oti, aot].join('.'));
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}
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get_mime() {
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return 'video/mp4; codecs="' + this.get_codec_string() + '"';
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}
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get_codec_string() {
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return this.codecs.join(', ');
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}
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parse_into(name, header_offset) {
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this.parse_until(name);
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this.idx += header_offset;
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}
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parse_until(name) {
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let curr_head = null;
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while (this.idx + 8 < this.data.byteLength) {
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curr_head = this.read_next_head();
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if (curr_head.name == name) {
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return true;
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} else {
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this.idx += curr_head.len;
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}
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}
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return false;
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}
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read_next_head() {
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return {"len": this.data.getUint32(this.idx), "name": this.data.getString(this.idx + 4, 4)};
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}
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}
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