diff --git a/lib/mss/mss_parser.js b/lib/mss/mss_parser.js
index 356cd8f91f..0f3260d740 100644
--- a/lib/mss/mss_parser.js
+++ b/lib/mss/mss_parser.js
@@ -632,6 +632,7 @@ shaka.mss.MssParser = class {
           timescale: stream.mssPrivateData.timescale,
           duration: stream.mssPrivateData.duration,
           videoNalus: videoNalus,
+          audioConfig: new Uint8Array([]),
           data: null, // Data is not necessary for init segement.
           stream: stream,
         };
diff --git a/lib/transmuxer/mp3_transmuxer.js b/lib/transmuxer/mp3_transmuxer.js
index c5d3b18bb1..3323348e0f 100644
--- a/lib/transmuxer/mp3_transmuxer.js
+++ b/lib/transmuxer/mp3_transmuxer.js
@@ -170,6 +170,7 @@ shaka.transmuxer.Mp3Transmuxer = class {
       timescale: sampleRate,
       duration: duration,
       videoNalus: [],
+      audioConfig: new Uint8Array([]),
       data: {
         sequenceNumber: this.frameIndex_,
         baseMediaDecodeTime: baseMediaDecodeTime,
diff --git a/lib/util/mp4_generator.js b/lib/util/mp4_generator.js
index 50ff84d7c5..7bfc375806 100644
--- a/lib/util/mp4_generator.js
+++ b/lib/util/mp4_generator.js
@@ -33,6 +33,9 @@ shaka.util.Mp4Generator = class {
     /** @private {!Array.<string>} */
     this.videoNalus_ = streamInfo.videoNalus;
 
+    /** @private {!Uint8Array} */
+    this.audioConfig_ = streamInfo.audioConfig;
+
     /** @private {number} */
     this.sequenceNumber_ = 0;
 
@@ -310,6 +313,10 @@ shaka.util.Mp4Generator = class {
         this.stream_.codecs.includes('mp3') ||
         this.stream_.codecs.includes('mp4a.40.34')) {
           bytes = this.mp3_();
+        } else if (this.stream_.codecs.includes('ac-3')) {
+          bytes = this.ac3_();
+        } else if (this.stream_.codecs.includes('ec-3')) {
+          bytes = this.ec3_();
         } else {
           bytes = this.mp4a_();
         }
@@ -471,6 +478,50 @@ shaka.util.Mp4Generator = class {
     return Mp4Generator.box('.mp3', this.audioStsd_());
   }
 
+  /**
+   * Generate a AC-3 box
+   *
+   * @return {!Uint8Array}
+   * @private
+   */
+  ac3_() {
+    const Mp4Generator = shaka.util.Mp4Generator;
+    const dac3Box = Mp4Generator.box('dac3', this.audioConfig_);
+
+    let sinfBox = new Uint8Array([]);
+    if (this.stream_.encrypted) {
+      sinfBox = this.sinf_();
+    }
+
+    let boxName = 'ac-3';
+    if (this.stream_.encrypted) {
+      boxName = 'enca';
+    }
+    return Mp4Generator.box(boxName, this.audioStsd_(), dac3Box, sinfBox);
+  }
+
+  /**
+   * Generate a EC-3 box
+   *
+   * @return {!Uint8Array}
+   * @private
+   */
+  ec3_() {
+    const Mp4Generator = shaka.util.Mp4Generator;
+    const dec3Box = Mp4Generator.box('dec3', this.audioConfig_);
+
+    let sinfBox = new Uint8Array([]);
+    if (this.stream_.encrypted) {
+      sinfBox = this.sinf_();
+    }
+
+    let boxName = 'ec-3';
+    if (this.stream_.encrypted) {
+      boxName = 'enca';
+    }
+    return Mp4Generator.box(boxName, this.audioStsd_(), dec3Box, sinfBox);
+  }
+
   /**
    * Generate a MP4A box
    *
@@ -479,7 +530,12 @@ shaka.util.Mp4Generator = class {
    */
   mp4a_() {
     const Mp4Generator = shaka.util.Mp4Generator;
-    const esdsBox = Mp4Generator.box('esds', this.esds_());
+    let esdsBox;
+    if (this.audioConfig_.byteLength > 0) {
+      esdsBox = Mp4Generator.box('esds', this.audioConfig_);
+    } else {
+      esdsBox = Mp4Generator.box('esds', this.esds_());
+    }
 
     let sinfBox = new Uint8Array([]);
     if (this.stream_.encrypted) {
@@ -1144,6 +1200,7 @@ shaka.util.Mp4Generator.DINF_ = new Uint8Array([]);
  *    timescale: number,
  *    duration: number,
  *    videoNalus: !Array.<string>,
+ *    audioConfig: !Uint8Array,
  *    data: ?shaka.util.Mp4Generator.Data,
  *    stream: !shaka.extern.Stream
  * }}
@@ -1154,6 +1211,8 @@ shaka.util.Mp4Generator.DINF_ = new Uint8Array([]);
  *   The Stream's duration.
  * @property {!Array.<string>} videoNalus
  *   The stream's video nalus.
+ * @property {!Uint8Array} audioConfig
+ *   The stream's audio config.
  * @property {?shaka.util.Mp4Generator.Data} data
  *   The stream's data.
  * @property {!shaka.extern.Stream} stream