8000 feat: support emsg box parsing · videojs/mux.js@2e77285 · GitHub
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feat: support emsg box parsing
1 parent 2e50704 commit 2e77285

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2 files changed

+85
-2
lines changed

2 files changed

+85
-2
lines changed

‎lib/mp4/emsg.js

+76
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,76 @@
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var parseStringUntilNullChar = function(data) {
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var index = 0;
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var curChar = String.fromCharCode(data[index]);
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var retString = '';
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while (curChar !== '\0') {
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retString += curChar;
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index++;
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curChar = String.fromCharCode(data[index]);
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}
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// Add nullChar
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retString += curChar;
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return retString;
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};
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var parseEmsgBox = function(boxData) {
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var offset = 0
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var version = boxData[offset];
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var scheme_id_uri, value, timescale, presentation_time, presentation_time_delta, event_duration, id;
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// version 0 vs version 1 have different formats.
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if (version === 0) {
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// Parse id and value strings first.
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scheme_id_uri = parseStringUntilNullChar(boxData);
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offset += scheme_id_uri.length - 1;
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value = parseStringUntilNullChar(boxData.subarray(offset));
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var dv = new DataView(boxData);
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timescale = dv.getUint32(12);
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presentation_time_delta = dv.getUint32(16);
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event_duration = dv.getUint32(20);
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id = dv.getUint32(24);
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offset = 28;
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} else if (version === 1) {
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var dv = new DataView(boxData);
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timescale = dv.getUint32(0);
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presentation_time = dv.getBigUint64(4);
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event_duration = dv.getUint32(12);
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id = dv.getUint32(16);
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offset = 20;
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scheme_id_uri = parseStringUntilNullChar(boxData.subarray(offset));
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offset += scheme_id_uri.length - 1;
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value = parseStringUntilNullChar(boxData.subarray(offset));
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offset += value.length - 1;
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}
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var message_data = boxData.subarray(offset, boxData.byteLength);
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return { scheme_id_uri, value,
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timescale, presentation_time,
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presentation_time_delta,
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event_duration, id,
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message_data };
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};
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var scaleTime = function(presentationTime, timescale, timeDelta, offset) {
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return presentationTime ? presentationTime / timescale : offset + timeDelta / timescale;
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};
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// TODO: This may need to return more ID3 specific data rather than just data, pts, duration.
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var getEmsgData = function(data, ptOffset) {
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var emsgBoxes = findBox(data, ['emsg']);
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var parsedBoxes = [];
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emsgBoxes.forEach(function(boxData) {
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// TODO: We may need to check for ID3 specific schemeIdURI before returning data.
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var parsedBox = parseEmsgBox(boxData);
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var pts = scaleTime(parsedBox.presentation_time, parsedBox.timescale, parsedBox.presentation_time_delta, ptOffset);
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var duration = scaleTime(parsedBox.duration, parsedBox.timescale);
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parsedBoxes.push({
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data: parsedBox.message_data,
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pts,
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duration,
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});
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});
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return parsedBoxes;
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};
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module.exports = getEmsgData;

‎lib/mp4/probe.js

+9-2
5B40
Original file line numberDiff line numberDiff line change
@@ -16,8 +16,9 @@ var parseTfhd = require('../tools/parse-tfhd.js');
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var parseTrun = require('../tools/parse-trun.js');
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var parseTfdt = require('../tools/parse-tfdt.js');
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var getUint64 = require('../utils/numbers.js').getUint64;
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var getEmsgData = require('../mp4/emsg.js');
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var timescale, startTime, compositionStartTime, getVideoTrackIds, getTracks,
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getTimescaleFromMediaHeader;
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getTimescaleFromMediaHeader, getEmsg;
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var window = require('global/window');
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2324

@@ -370,6 +371,11 @@ getTracks = function(init) {
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return tracks;
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};
372373

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// TODO: If we are returning specific ID3 emsg data lets modify the function signature.
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getEmsg = function(segmentData, ptOffset) {
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return getEmsgData(segmentData, ptOffset);
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};
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module.exports = {
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// export mp4 inspector's findBox and parseType for backwards compatibility
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findBox: findBox,
@@ -379,5 +385,6 @@ module.exports = {
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compositionStartTime: compositionStartTime,
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videoTrackIds: getVideoTrackIds,
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tracks: getTracks,
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getTimescaleFromMediaHeader: getTimescaleFromMediaHeader
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getTimescaleFromMediaHeader: getTimescaleFromMediaHeader,
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getEmsg: getEmsg,
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};

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