mp4-remuxer / remuxAudio() : recompute mdatSize / dont rely on audioT…

…rack.len (video-dev#2096)

* mp4-remuxer / remuxAudio() : dont rely on track.len to compute mdatSize

recompute it by looping through all samples and summing their individual size

get rid of track.len as it should now be useless

related to video-dev#2063

src/demux/adts.js

@@ -229,8 +229,6 @@ export function appendFrame (track, data, offset, pts, frameIndex) {
     };
 
     track.samples.push(aacSample);
-    track.len += frameLength;
-
     return { sample: aacSample, length: frameLength + headerLength };
   }
 

src/demux/mpegaudio.js

@@ -67,7 +67,6 @@ const MpegAudio = {
       track.channelCount = header.channelCount;
       track.samplerate = header.sampleRate;
       track.samples.push(sample);
-      track.len += header.frameLength;
 
       return { sample, length: header.frameLength };
     }

src/demux/tsdemuxer.js

@@ -94,7 +94,6 @@ class TSDemuxer {
       inputTimeScale: 90000,
       sequenceNumber: 0,
       samples: [],
-      len: 0,
       dropped: type === 'video' ? 0 : undefined,
       isAAC: type === 'audio' ? true : undefined,
       duration: type === 'audio' ? duration : undefined

src/remux/mp4-remuxer.js

@@ -393,7 +393,6 @@ class MP4Remuxer {
     // next AVC sample DTS should be equal to last sample DTS + last sample duration (in PES timescale)
     this.nextAvcDts = lastDTS + mp4SampleDuration;
     let dropped = track.dropped;
-    track.len = 0;
     track.nbNalu = 0;
     track.dropped = 0;
     if (outputSamples.length && navigator.userAgent.toLowerCase().indexOf('chrome') > -1) {
@@ -434,11 +433,11 @@ class MP4Remuxer {
     const initPTS = this._initPTS;
     const rawMPEG = !track.isAAC && this.typeSupported.mpeg;
 
-    let offset,
-      mp4Sample,
+    let mp4Sample,
       fillFrame,
       mdat, moof,
       firstPTS, lastPTS,
+      offset = (rawMPEG ? 0 : 8),
       inputSamples = track.samples,
       outputSamples = [],
       nextAudioPts = this.nextAudioPts;
@@ -503,7 +502,6 @@ class MP4Remuxer {
         if (delta <= -maxAudioFramesDrift * inputSampleDuration) {
           logger.warn(`Dropping 1 audio frame @ ${(nextPts / inputTimeScale).toFixed(3)}s due to ${Math.round(duration)} ms overlap.`);
           inputSamples.splice(i, 1);
-          track.len -= sample.unit.length;
           // Don't touch nextPtsNorm or i
         } // eslint-disable-line brace-style
 
@@ -522,7 +520,6 @@ class MP4Remuxer {
               fillFrame = sample.unit.subarray();
             }
             inputSamples.splice(i, 0, { unit: fillFrame, pts: newStamp, dts: newStamp });
-            track.len += fillFrame.length;
             nextPts += inputSampleDuration;
             i++;
           }
@@ -543,6 +540,13 @@ class MP4Remuxer {
       }
     }
 
+    // compute mdat size, as we eventually filtered/added some samples
+    let nbSamples = inputSamples.length;
+    let mdatSize = 0;
+    while (nbSamples--) {
+      mdatSize += inputSamples[nbSamples].unit.byteLength;
+    }
+
     for (let j = 0, nbSamples = inputSamples.length; j < nbSamples; j++) {
       let audioSample = inputSamples[j];
       let unit = audioSample.unit;
@@ -568,13 +572,13 @@ class MP4Remuxer {
                   fillFrame = unit.subarray();
                 }
 
-                track.len += numMissingFrames * fillFrame.length;
+                mdatSize += numMissingFrames * fillFrame.length;
               }
               // if we have frame overlap, overlapping for more than half a frame duraion
             } else if (delta < -12) {
               // drop overlapping audio frames... browser will deal with it
               logger.log(`drop overlapping AAC sample, expected/parsed/delta:${(nextAudioPts / inputTimeScale).toFixed(3)}s/${(pts / inputTimeScale).toFixed(3)}s/${(-delta)}ms`);
-              track.len -= unit.byteLength;
+              mdatSize -= unit.byteLength;
               continue;
             }
             // set PTS/DTS to expected PTS/DTS
@@ -583,11 +587,8 @@ class MP4Remuxer {
         }
         // remember first PTS of our audioSamples
         firstPTS = pts;
-        if (track.len > 0) {
-          /* concatenate the audio data and construct the mdat in place
-            (need 8 more bytes to fill length and mdat type) */
-          let mdatSize = rawMPEG ? track.len : track.len + 8;
-          offset = rawMPEG ? 0 : 8;
+        if (mdatSize > 0) {
+          mdatSize += offset;
           try {
             mdat = new Uint8Array(mdatSize);
           } catch (err) {
@@ -646,7 +647,7 @@ class MP4Remuxer {
       lastPTS = pts;
     }
     let lastSampleDuration = 0;
-    let nbSamples = outputSamples.length;
+    nbSamples = outputSamples.length;
     // set last sample duration as being identical to previous sample
     if (nbSamples >= 2) {
       lastSampleDuration = outputSamples[nbSamples - 2].duration;
@@ -656,7 +657,6 @@ class MP4Remuxer {
       // next audio sample PTS should be equal to last sample PTS + duration
       this.nextAudioPts = nextAudioPts = lastPTS + scaleFactor * lastSampleDuration;
       // logger.log('Audio/PTS/PTSend:' + audioSample.pts.toFixed(0) + '/' + this.nextAacDts.toFixed(0));
-      track.len = 0;
       track.samples = outputSamples;
       if (rawMPEG) {
         moof = new Uint8Array();
@@ -715,7 +715,6 @@ class MP4Remuxer {
     for (let i = 0; i < nbSamples; i++) {
       let stamp = startDTS + i * frameDuration;
       samples.push({ unit: silentFrame, pts: stamp, dts: stamp });
-      track.len += silentFrame.length;
     }
     track.samples = samples;
 

tests/unit/demuxer/adts.js

@@ -394,7 +394,6 @@ describe('appendFrame', function () {
       length: 16
     });
     expect(track.samples.length).to.equal(1);
-    expect(track.len).to.equal(7);
   });
 
   it('should not append sample if `parseFrameHeader` fails', function () {
@@ -410,6 +409,5 @@ describe('appendFrame', function () {
 
     expect(appendFrame(track, data, 0, 0, 0)).to.be.undefined;
     expect(track.samples.length).to.equal(0);
-    expect(track.len).to.equal(0);
   });
 });