Fix getVideoStartPts when timestamps wrap at MPEG-2 33-bit boundary

src/remux/mp4-remuxer.ts

@@ -100,20 +100,24 @@ export default class MP4Remuxer implements Remuxer {
     this.videoTrackConfig = undefined;
   }
 
-  getVideoStartPts(videoSamples) {
+  getVideoStartPts(videoSamples: VideoSample[]) {
+    // Get the minimum PTS value relative to the first sample's PTS, normalized for 33-bit wrapping
     let rolloverDetected = false;
+    const firstPts = videoSamples[0].pts;
     const startPTS = videoSamples.reduce((minPTS, sample) => {
-      const delta = sample.pts - minPTS;
+      let pts = sample.pts;
+      let delta = pts - minPTS;
       if (delta < -4294967296) {
         // 2^32, see PTSNormalize for reasoning, but we're hitting a rollover here, and we don't want that to impact the timeOffset calculation
         rolloverDetected = true;
-        return normalizePts(minPTS, sample.pts);
-      } else if (delta > 0) {
+        pts = normalizePts(pts, firstPts);
+        delta = pts - minPTS;
+      }
+      if (delta > 0) {
         return minPTS;
-      } else {
-        return sample.pts;
       }
-    }, videoSamples[0].pts);
+      return pts;
+    }, firstPts);
     if (rolloverDetected) {
       this.logger.debug('PTS rollover detected');
     }

tests/index.js

@@ -35,6 +35,7 @@ import './unit/loader/fragment-loader';
 import './unit/loader/fragment';
 import './unit/loader/level';
 import './unit/loader/playlist-loader';
+import './unit/remux/mp4-remuxer';
 import './unit/utils/attr-list';
 import './unit/utils/binary-search';
 import './unit/utils/buffer-helper';

tests/unit/remux/mp4-remuxer.ts

@@ -0,0 +1,93 @@
+import chai from 'chai';
+import EventEmitter from 'eventemitter3';
+import sinonChai from 'sinon-chai';
+import { hlsDefaultConfig } from '../../../src/config';
+import MP4Remuxer from '../../../src/remux/mp4-remuxer';
+import { logger } from '../../../src/utils/logger';
+import type { HlsEventEmitter } from '../../../src/events';
+import type { VideoSample } from '../../../src/types/demuxer';
+import type { TypeSupported } from '../../../src/utils/codecs';
+
+chai.use(sinonChai);
+const expect = chai.expect;
+
+describe('mp4-remuxer', function () {
+  let mp4Remuxer: MP4Remuxer;
+
+  beforeEach(function () {
+    const observer: HlsEventEmitter = new EventEmitter() as HlsEventEmitter;
+    const config = { ...hlsDefaultConfig };
+    const typeSupported: TypeSupported = {
+      mpeg: true,
+      mp3: true,
+      ac3: true,
+    };
+    mp4Remuxer = new MP4Remuxer(observer, config, typeSupported, logger);
+  });
+
+  afterEach(function () {
+    mp4Remuxer.destroy();
+  });
+
+  it('should find the lowest PTS in video samples', function () {
+    const videoSamples = [ptsDts(0, 0), ptsDts(3003, 3003), ptsDts(6006, 6006)];
+    const minPts = mp4Remuxer.getVideoStartPts(videoSamples);
+    expect(minPts).to.eq(0);
+  });
+
+  it('should find the lowest PTS in video samples with decrementing PTS samples', function () {
+    const videoSamples = [
+      ptsDts(3003, 0),
+      ptsDts(1001, 3003),
+      ptsDts(6006, 6006),
+    ];
+    const minPts = mp4Remuxer.getVideoStartPts(videoSamples);
+    expect(minPts).to.eq(1001);
+  });
+
+  it('should find the lowest normalized PTS in video samples with wrapping timestamps 1/2', function () {
+    const videoSamples = [
+      ptsDts(8589925344, 8589922341),
+      ptsDts(2765, 8589925344),
+      ptsDts(8589931350, 8589928347),
+      ptsDts(8589934353, 8589931350),
+      ptsDts(11774, 8589934353),
+      ptsDts(5768, 2765),
+      ptsDts(8771, 5768),
+      ptsDts(14777, 8771),
+    ];
+    const minPts = mp4Remuxer.getVideoStartPts(videoSamples);
+    expect(minPts).to.eq(8589925344);
+    expect(minPts).to.lessThanOrEqual(8589925344);
+  });
+
+  it('should find the lowest normalized PTS in video samples with wrapping timestamps 2/2', function () {
+    const videoSamples = [
+      ptsDts(8589931350, 8589922341),
+      ptsDts(8589928347, 8589928347),
+      ptsDts(8589934353, 8589931350),
+      ptsDts(11774, 8589934353),
+      ptsDts(5768, 2765),
+      ptsDts(8771, 5768),
+      ptsDts(14777, 8771),
+    ];
+    const minPts = mp4Remuxer.getVideoStartPts(videoSamples);
+    expect(minPts).to.eq(8589928347);
+  });
+});
+
+function ptsDts(pts: number, dts: number): VideoSample {
+  return {
+    dts,
+    pts,
+    key: true,
+    frame: true,
+    units: [
+      {
+        data: new Uint8Array(1),
+        type: 0,
+      },
+    ],
+    length: 1,
+  };
+}