add cmaf id3 in emsg support for hls.js

monyone · Jul 2, 2021 · f361dd9 · f361dd9
1 parent c36cf9f
commit f361dd9
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diff --git a/src/remux/passthrough-remuxer.ts b/src/remux/passthrough-remuxer.ts
@@ -4,6 +4,7 @@ import {
   getStartDTS,
   offsetStartDTS,
   parseInitSegment,
+  parseId3TrackSamples,
 } from '../utils/mp4-tools';
 import { ElementaryStreamTypes } from '../loader/fragment';
 import { logger } from '../utils/logger';
@@ -199,6 +200,28 @@ class PassThroughRemuxer implements Remuxer {
       dropped: 0,
     };
 
+    if (this.initPTS != null) {
+      const samples = parseId3TrackSamples(data);
+
+      for (let index = 0; index < samples.length; index++) {
+        const sample = samples[index];
+        if (sample == null) {
+          continue;
+        }
+        if (sample.timescale == null) {
+          continue;
+        }
+
+        sample.pts = sample.pts / sample.timescale - this.initPTS;
+        sample.dts = sample.dts / sample.timescale - this.initPTS;
+        sample.duration =
+          sample.duration != null
+            ? sample.duration / sample.timescale
+            : undefined;
+        id3Track.samples.push(sample);
+      }
+    }
+
     result.audio = track.type === 'audio' ? track : undefined;
     result.video = track.type !== 'audio' ? track : undefined;
     result.text = textTrack;

diff --git a/src/utils/mp4-tools.ts b/src/utils/mp4-tools.ts
@@ -9,11 +9,26 @@ type Mp4BoxData = {
 
 const UINT32_MAX = Math.pow(2, 32) - 1;
 const push = [].push;
+const ID3_SCHEME_ID_URIS = [
+  'https://aomedia.org/emsg/ID3',
+  'https://developer.apple.com/streaming/emsg-id3',
+];
 
 export function bin2str(data: Uint8Array): string {
   return String.fromCharCode.apply(null, data);
 }
 
+export function readNullTerminatedString(buffer, offset): string {
+  let i = offset;
+
+  while (String.fromCharCode(buffer[i]) !== '\0' && i < buffer.byteLength) {
+    i++;
+  }
+
+  const val = new Uint8Array(buffer.subarray(offset, i));
+  return bin2str(val);
+}
+
 export function readUint16(
   buffer: Uint8Array | Mp4BoxData,
   offset: number
@@ -112,6 +127,60 @@ export function findBox(
   return results;
 }
 
+export function parseId3TrackSamples(data) {
+  const emsgs = findBox(data, ['emsg']);
+  return emsgs.map((emsg) => {
+    try {
+      const data = emsg.data.subarray(emsg.start, emsg.end);
+      let offset = 0;
+
+      const view = new DataView(data.buffer, data.byteOffset, data.byteLength);
+      const version = view.getUint8(offset);
+      if (version !== 1) {
+        return undefined;
+      }
+
+      // skip over 3 bytes of flags
+      offset += 4;
+      const timescale = view.getUint32(offset);
+      offset += 4;
+      const presentationTime = Number(view.getBigUint64(offset));
+      offset += 8;
+      const eventDuration = view.getUint32(offset);
+      offset += 4;
+      const id = view.getUint32(offset);
+      offset += 4;
+      const schemeIdUri = readNullTerminatedString(data, offset);
+      if (!ID3_SCHEME_ID_URIS.includes(schemeIdUri)) {
+        return undefined;
+      }
+
+      // skip over the null byte
+      offset += schemeIdUri.length + 1;
+      const value = readNullTerminatedString(data, offset);
+      // skip over the null byte
+      offset += value.length + 1;
+      // the rest is id3 payload
+      const messageData = new Uint8Array(
+        data.subarray(offset, data.byteLength)
+      );
+
+      return {
+        timescale,
+        pts: presentationTime,
+        dts: presentationTime,
+        duration: eventDuration !== 0xffffffff ? eventDuration : undefined,
+        id,
+        schemeIdUri,
+        value,
+        data: messageData,
+      };
+    } catch (e) {
+      return undefined;
+    }
+  });
+}
+
 type SidxInfo = {
   earliestPresentationTime: number;
   timescale: number;