From d17649ec2c79356dce64bb1efa6ed9c9fdbf1cc9 Mon Sep 17 00:00:00 2001
From: Brion Vibber <brion@pobox.com>
Date: Fri, 24 May 2019 12:02:28 -0700
Subject: [PATCH 1/2] Cache buffer.byteLength in NalByteStream.push

Significant speedup in (pre-Chromium) Edge, especially for high
bitrates such as uncompressed or lightly-compressed frames.

Previously, buffer.byteLength and buffer.length got looked up
multiple times per byte processed in Edge, leading to higher
CPU usage.
---
 lib/codecs/h264.js | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/lib/codecs/h264.js b/lib/codecs/h264.js
index 1b66cdad..ec619c8a 100644
--- a/lib/codecs/h264.js
+++ b/lib/codecs/h264.js
@@ -40,6 +40,7 @@ NalByteStream = function() {
       swapBuffer.set(data.data, buffer.byteLength);
       buffer = swapBuffer;
     }
+    var len = buffer.byteLength;
 
     // Rec. ITU-T H.264, Annex B
     // scan for NAL unit boundaries
@@ -52,7 +53,7 @@ NalByteStream = function() {
     // ^ sync point        ^ i
 
     // advance the sync point to a NAL start, if necessary
-    for (; syncPoint < buffer.byteLength - 3; syncPoint++) {
+    for (; syncPoint < len - 3; syncPoint++) {
       if (buffer[syncPoint + 2] === 1) {
         // the sync point is properly aligned
         i = syncPoint + 5;
@@ -60,7 +61,7 @@ NalByteStream = function() {
       }
     }
 
-    while (i < buffer.byteLength) {
+    while (i < len) {
       // look at the current byte to determine if we've hit the end of
       // a NAL unit boundary
       switch (buffer[i]) {
@@ -82,7 +83,7 @@ NalByteStream = function() {
         // drop trailing zeroes
         do {
           i++;
-        } while (buffer[i] !== 1 && i < buffer.length);
+        } while (buffer[i] !== 1 && i < len);
         syncPoint = i - 2;
         i += 3;
         break;

From 46e4327a2c6c33feaf9b50a7848a34cbb38c9bbf Mon Sep 17 00:00:00 2001
From: Brion Vibber <brion@pobox.com>
Date: Sat, 1 Jun 2019 02:16:08 -0700
Subject: [PATCH 2/2] Basic support for FLAC-in-MP4 audio tracks

Allows for creating an MP4 stream with FLAC contents using
the MP4 box generation functions or AudioSegmentStream.

Use codec string 'fLaC' and specify a 'metadata' field in the
track info with the FLAC METADATA_BLOCK_HEADER fields to go
into the dfLa box.

See https://github.com/xiph/flac/blob/master/doc/isoflac.txt
for details of the MP4 embedding of FLAC audio.

Also allows variable-length audio packets in AudioSegmentStream

FLAC may have variable-length packets, so allow passing a
duration in samples on incoming frames.

This gets FLAC with, say, 960 samples per frame working
consistently in Firefox and Chrome.
---
 lib/mp4/audio-frame-utils.js |  2 +-
 lib/mp4/mp4-generator.js     | 22 +++++++++++++++++++---
 2 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/lib/mp4/audio-frame-utils.js b/lib/mp4/audio-frame-utils.js
index faa5f4ab..93813d3f 100644
--- a/lib/mp4/audio-frame-utils.js
+++ b/lib/mp4/audio-frame-utils.js
@@ -121,7 +121,7 @@ var generateSampleTable = function(frames) {
     currentFrame = frames[i];
     samples.push({
       size: currentFrame.data.byteLength,
-      duration: 1024 // For AAC audio, all samples contain 1024 samples
+      duration: currentFrame.duration || 1024 // For AAC audio, all samples contain 1024 samples
     });
   }
   return samples;
diff --git a/lib/mp4/mp4-generator.js b/lib/mp4/mp4-generator.js
index 032a7ba2..74f4806f 100644
--- a/lib/mp4/mp4-generator.js
+++ b/lib/mp4/mp4-generator.js
@@ -11,7 +11,7 @@
 
 var UINT32_MAX = Math.pow(2, 32) - 1;
 
-var box, dinf, esds, ftyp, mdat, mfhd, minf, moof, moov, mvex, mvhd,
+var box, dfLa, dinf, esds, ftyp, mdat, mfhd, minf, moof, moov, mvex, mvhd,
     trak, tkhd, mdia, mdhd, hdlr, sdtp, stbl, stsd, traf, trex,
     trun, types, MAJOR_BRAND, MINOR_VERSION, AVC1_BRAND, VIDEO_HDLR,
     AUDIO_HDLR, HDLR_TYPES, VMHD, SMHD, DREF, STCO, STSC, STSZ, STTS;
@@ -23,10 +23,12 @@ var box, dinf, esds, ftyp, mdat, mfhd, minf, moof, moov, mvex, mvhd,
     avc1: [], // codingname
     avcC: [],
     btrt: [],
+    dfLa: [],
     dinf: [],
     dref: [],
     esds: [],
     ftyp: [],
+    fLaC: [],
     hdlr: [],
     mdat: [],
     mdhd: [],
@@ -184,6 +186,13 @@ box = function(type) {
   return result;
 };
 
+dfLa = function(track) {
+  return box(types.dfLa, new Uint8Array([
+    0x00, // version
+    0x00, 0x00, 0x00 // flags
+  ]), track.metadata || []);
+};
+
 dinf = function() {
   return box(types.dinf, box(types.dref, DREF));
 };
@@ -465,7 +474,10 @@ stbl = function(track) {
   };
 
   audioSample = function(track) {
-    return box(types.mp4a, new Uint8Array([
+    var audioSampleBox = new Uint8Array([
+
+      // FLACSampleEntry extends AudioSampleEntry
+      // https://github.com/xiph/flac/blob/master/doc/isoflac.txt
 
       // SampleEntry, ISO/IEC 14496-12
       0x00, 0x00, 0x00,
@@ -488,7 +500,11 @@ stbl = function(track) {
       0x00, 0x00 // samplerate, 16.16
 
       // MP4AudioSampleEntry, ISO/IEC 14496-14
-    ]), esds(track));
+    ]);
+    if (track.codec === 'fLaC') {
+      return box(types.fLaC, audioSampleBox, dfLa(track));
+    }
+    return box(types.mp4a, audioSampleBox, esds(track));
   };
 }());