feat: parse edts boxes (#375)

Author: Nikola Hristov

lib/tools/mp4-inspector.js

@@ -9,6 +9,8 @@
  */
 'use strict';
 
+var MAX_UINT32 = Math.pow(2, 32);
+
 var
   inspectMp4,
   textifyMp4,
@@ -123,6 +125,40 @@ var
         avgBitrate: view.getUint32(8)
       };
     },
+    edts: function edts(data) {
+      return {
+        boxes: inspectMp4(data)
+      };
+    },
+    elst: function elst(data) {
+      var
+        view = new DataView(data.buffer, data.byteOffset, data.byteLength),
+        result = {
+          version: view.getUint8(0),
+          flags: new Uint8Array(data.subarray(1, 4)),
+          edits: []
+        },
+        entryCount = view.getUint32(4),
+        i;
+      for (i = 8; entryCount; entryCount--) {
+        if (result.version === 0) {
+          result.edits.push({
+            segmentDuration: view.getUint32(i),
+            mediaTime: view.getInt32(i + 4),
+            mediaRate: view.getUint16(i + 8) + view.getUint16(i + 10) / (256 * 256)
+          });
+          i += 12;
+        } else {
+          result.edits.push({
+            segmentDuration: (view.getUint32(i) * MAX_UINT32) + view.getUint32(i + 4),
+            mediaTime: (view.getUint32(i + 8) * MAX_UINT32) + view.getUint32(i + 12),
+            mediaRate: view.getUint16(i + 16) + view.getUint16(i + 18) / (256 * 256)
+          });
+          i += 20;
+        }
+      }
+      return result;
+    },
     esds: function(data) {
       return {
         version: data[0],

test/mp4-inspector.test.js

@@ -215,7 +215,7 @@ QUnit.test('can parse a moov', function(assert) {
   var result = QUnit.dump.parse(mp4.tools.inspect(new Uint8Array(data)));
   var expected = QUnit.dump.parse([{
     type: 'moov',
-    size: 981,
+    size: 1061,
     boxes: [{
       type: 'mvhd',
       version: 1,
@@ -231,7 +231,7 @@ QUnit.test('can parse a moov', function(assert) {
       nextTrackId: 2
     }, {
       type: 'trak',
-      size: 439,
+      size: 475,
       boxes: [{
         type: 'tkhd',
         flags: new Uint8Array([0, 0, 0]),
@@ -247,6 +247,20 @@ QUnit.test('can parse a moov', function(assert) {
         matrix: new Uint32Array(unityMatrix),
         width: 300,
         height: 150
+      }, {
+        type: 'edts',
+        size: 36,
+        boxes: [{
+          type: 'elst',
+          size: 28,
+          version: 0,
+          flags: new Uint8Array([0, 0, 0]),
+          edits: [{
+            segmentDuration: 0,
+            mediaTime: 1024,
+            mediaRate: 1.5
+          }]
+        }]
       }, {
         type: 'mdia',
         size: 327,
@@ -349,7 +363,7 @@ QUnit.test('can parse a moov', function(assert) {
       }]
     }, {
       type: 'trak',
-      size: 414,
+      size: 458,
       boxes: [{
         type: 'tkhd',
         flags: new Uint8Array([0, 0, 0]),
@@ -365,6 +379,20 @@ QUnit.test('can parse a moov', function(assert) {
         matrix: new Uint32Array(unityMatrix),
         width: 300,
         height: 150
+      }, {
+        type: 'edts',
+        size: 44,
+        boxes: [{
+          type: 'elst',
+          size: 36,
+          version: 1,
+          flags: new Uint8Array([0, 0, 0]),
+          edits: [{
+            segmentDuration: 0,
+            mediaTime: 1152921504606847000,
+            mediaRate: 1.5
+          }]
+        }]
       }, {
         type: 'mdia',
         size: 302,

test/utils/mp4-helpers.js

@@ -109,6 +109,14 @@ module.exports.sampleMoov =
               unityMatrix,
               0x01, 0x2c, 0x00, 0x00, // 300 in 16.16 fixed-point
               0x00, 0x96, 0x00, 0x00), // 150 in 16.16 fixed-point
+          box('edts',
+              box('elst',
+                0x00, // version
+                0x00, 0x00, 0x00, // flags
+                0x00, 0x00, 0x00, 0x01, // entry_count
+                0x00, 0x00, 0x00, 0x00, // segment_duration
+                0x00, 0x00, 0x04, 0x00, // media_time
+                0x00, 0x01, 0x80, 0x00)), // media_rate
           box('mdia',
               box('mdhd',
                   0x01, // version 1
@@ -208,6 +216,14 @@ module.exports.sampleMoov =
               unityMatrix,
               0x01, 0x2c, 0x00, 0x00, // 300 in 16.16 fixed-point
               0x00, 0x96, 0x00, 0x00), // 150 in 16.16 fixed-point
+          box('edts',
+              box('elst',
+                  0x01, // version
+                  0x00, 0x00, 0x00, // flags
+                  0x00, 0x00, 0x00, 0x01, // entry_count
+                  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // segment_duration
+                  0x10, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // media_time
+                  0x00, 0x01, 0x80, 0x00)), // media_rate
           box('mdia',
               box('mdhd',
                   0x01, // version 1