FLAC and Opus support

This adds the MP4-registered codec entry "fLaC", as well as the
non-registered codec entries "flac" and "FLAC".

Browsers added FLAC support before the MP4 Registration Authority listed
the codec entry "fLaC", and went with "flac". Bugs have been opened
with browsers to address this, but in order to deal with legacy
playlist manifests (they may list "flac" or even "FLAC"), this
replaces any instance of "flac" and "opus" (any case) with the first
compatible codec string.

Author: jprjr

src/controller/buffer-controller.ts

@@ -2,6 +2,7 @@ import { Events } from '../events';
 import { logger } from '../utils/logger';
 import { ErrorDetails, ErrorTypes } from '../errors';
 import { BufferHelper } from '../utils/buffer-helper';
+import { getCodecCompatibleName } from '../utils/codecs';
 import { getMediaSource } from '../utils/mediasource-helper';
 import { ElementaryStreamTypes } from '../loader/fragment';
 import type { TrackSet } from '../types/track';
@@ -29,6 +30,7 @@ import { LevelDetails } from '../loader/level-details';
 
 const MediaSource = getMediaSource();
 const VIDEO_CODEC_PROFILE_REPACE = /([ha]vc.)(?:\.[^.,]+)+/;
+const AUDIO_CODEC_REGEXP = /flac|opus/gi;
 
 export default class BufferController implements ComponentAPI {
   // The level details used to determine duration, target-duration and live
@@ -254,7 +256,14 @@ export default class BufferController implements ComponentAPI {
             '$1'
           );
           if (currentCodec !== nextCodec) {
-            const mimeType = `${container};codecs=${levelCodec || codec}`;
+            let trackCodec = levelCodec || codec;
+            if (trackName.indexOf('audio') !== -1) {
+              trackCodec = trackCodec.replace(
+                AUDIO_CODEC_REGEXP,
+                getCodecCompatibleName
+              );
+            }
+            const mimeType = `${container};codecs=${trackCodec}`;
             this.appendChangeType(trackName, mimeType);
             logger.log(
               `[buffer-controller]: switching codec ${currentCodec} to ${nextCodec}`
@@ -712,7 +721,12 @@ export default class BufferController implements ComponentAPI {
           );
         }
         // use levelCodec as first priority
-        const codec = track.levelCodec || track.codec;
+        let codec = track.levelCodec || track.codec;
+        if (codec) {
+          if (trackName.indexOf('audio') !== -1) {
+            codec = codec.replace(AUDIO_CODEC_REGEXP, getCodecCompatibleName);
+          }
+        }
         const mimeType = `${track.container};codecs=${codec}`;
         logger.log(`[buffer-controller]: creating sourceBuffer(${mimeType})`);
         try {

src/controller/level-controller.ts

@@ -14,7 +14,7 @@ import {
 import { Level } from '../types/level';
 import { Events } from '../events';
 import { ErrorTypes, ErrorDetails } from '../errors';
-import { isCodecSupportedInMp4 } from '../utils/codecs';
+import { isCodecSupportedInMp4, getCodecCompatibleName } from '../utils/codecs';
 import { addGroupId, assignTrackIdsByGroup } from './level-helper';
 import BasePlaylistController from './base-playlist-controller';
 import { PlaylistContextType, PlaylistLevelType } from '../types/loader';
@@ -26,6 +26,8 @@ const chromeOrFirefox: boolean = /chrome|firefox/.test(
   navigator.userAgent.toLowerCase()
 );
 
+const AUDIO_CODEC_REGEXP = /flac|opus/gi;
+
 export default class LevelController extends BasePlaylistController {
   private _levels: Level[] = [];
   private _firstLevel: number = -1;
@@ -109,6 +111,13 @@ export default class LevelController extends BasePlaylistController {
         levelParsed.audioCodec = undefined;
       }
 
+      if (levelParsed.audioCodec) {
+        levelParsed.audioCodec = levelParsed.audioCodec.replace(
+          AUDIO_CODEC_REGEXP,
+          getCodecCompatibleName
+        );
+      }
+
       const levelKey = `${levelParsed.bitrate}-${levelParsed.attrs.RESOLUTION}-${levelParsed.attrs.CODECS}`;
       levelFromSet = levelSet[levelKey];
 

src/controller/stream-controller.ts

@@ -1210,7 +1210,12 @@ export default class StreamController
         }
       }
       // HE-AAC is broken on Android, always signal audio codec as AAC even if variant manifest states otherwise
-      if (ua.indexOf('android') !== -1 && audio.container !== 'audio/mpeg') {
+      if (
+        audioCodec &&
+        audioCodec.indexOf('mp4a.40.5') !== -1 &&
+        ua.indexOf('android') !== -1 &&
+        audio.container !== 'audio/mpeg'
+      ) {
         // Exclude mpeg audio
         audioCodec = 'mp4a.40.2';
         this.log(`Android: force audio codec to ${audioCodec}`);

src/remux/passthrough-remuxer.ts

@@ -246,6 +246,12 @@ function getParsedTrackCodec(
   if (parsedCodec === 'avc1' || type === ElementaryStreamTypes.VIDEO) {
     return 'avc1.42e01e';
   }
+  if (parsedCodec === 'fLaC') {
+    return 'fLaC';
+  }
+  if (parsedCodec === 'Opus') {
+    return 'Opus';
+  }
   return 'mp4a.40.5';
 }
 export default PassThroughRemuxer;

src/utils/codecs.ts

@@ -14,6 +14,9 @@ const sampleEntryCodesISO = {
     dtsh: true,
     'ec-3': true,
     enca: true,
+    fLaC: true, // MP4-RA listed codec entry for FLAC
+    flac: true, // legacy browser codec name for FLAC
+    FLAC: true, // some manifests may list "FLAC" with Apple's tools
     g719: true,
     g726: true,
     m4ae: true,
@@ -83,3 +86,38 @@ export function isCodecSupportedInMp4(codec: string, type: CodecType): boolean {
     `${type || 'video'}/mp4;codecs="${codec}"`
   );
 }
+
+interface CodecNameCache {
+  flac?: string;
+  opus?: string;
+}
+
+const CODEC_COMPATIBLE_NAMES: CodecNameCache = {};
+
+type LowerCaseCodecType = 'flac' | 'opus';
+
+function getCodecCompatibleNameLower(
+  lowerCaseCodec: LowerCaseCodecType
+): string {
+  if (CODEC_COMPATIBLE_NAMES[lowerCaseCodec]) {
+    return CODEC_COMPATIBLE_NAMES[lowerCaseCodec]!;
+  }
+
+  const codecsToCheck = {
+    flac: ['fLaC', 'flac', 'FLAC'],
+    opus: ['Opus', 'opus'],
+  }[lowerCaseCodec];
+
+  for (let i = 0; i < codecsToCheck.length; i++) {
+    if (isCodecSupportedInMp4(codecsToCheck[i], 'audio')) {
+      CODEC_COMPATIBLE_NAMES[lowerCaseCodec] = codecsToCheck[i];
+      return codecsToCheck[i];
+    }
+  }
+
+  return lowerCaseCodec;
+}
+
+export function getCodecCompatibleName(codec: string): string {
+  return getCodecCompatibleNameLower(codec.toLowerCase() as LowerCaseCodecType);
+}