fix: calculating segment start time in live dash-mpd

fixes #21 again
fent · Dec 9, 2018 · 9dbd89a · 9dbd89a
1 parent 956e229
commit 9dbd89a
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Showing 5 changed files with 46 additions and 22 deletions.
diff --git a/lib/dash-mpd-parser.js b/lib/dash-mpd-parser.js
@@ -1,5 +1,6 @@
-const Writable = require('stream').Writable;
-const sax      = require('sax');
+const Writable  = require('stream').Writable;
+const sax       = require('sax');
+const parseTime = require('./parse-time');
 
 
 /**
@@ -20,9 +21,10 @@ module.exports = class DashMPDParser extends Writable {
     let segmentTemplate;
     let timescale, offset, duration, baseURL;
     let timeline = [];
-    let getSegments = false, startEmitted = false;
+    let getSegments = false;
     let isStatic;
     let treeLevel;
+    let periodStart;
 
     const tmpl = (str) => {
       const context = {
@@ -48,19 +50,13 @@ module.exports = class DashMPDParser extends Writable {
           offset = 0;
           baseURL = [];
           treeLevel = 0;
+          periodStart = parseTime.durationStr(node.attributes.start) || 0;
           break;
         case 'segmentlist':
           seq = parseInt(node.attributes.startnumber) || seq;
           timescale = parseInt(node.attributes.timescale) || timescale;
           duration = parseInt(node.attributes.duration) || duration;
           offset = parseInt(node.attributes.presentationtimeoffset) || offset;
-          if (!startEmitted) {
-            startEmitted = true;
-            if (offset) {
-              currtime += offset;
-            }
-            this.emit('starttime', currtime);
-          }
           break;
         case 'segmenttemplate':
           segmentTemplate = node.attributes;
@@ -84,6 +80,15 @@ module.exports = class DashMPDParser extends Writable {
             targetID = node.attributes.id;
           }
           getSegments = node.attributes.id === targetID + '';
+          if (getSegments) {
+            if (periodStart) {
+              currtime += periodStart;
+            }
+            if (offset) {
+              currtime -= offset / timescale * 1000;
+            }
+            this.emit('starttime', currtime);
+          }
           if (getSegments && segmentTemplate && timeline.length) {
             if (segmentTemplate.initialization) {
               this.emit('item', {

diff --git a/lib/index.js b/lib/index.js
@@ -27,7 +27,7 @@ module.exports = (playlistURL, options) => {
   }
   let relativeBegin = typeof options.begin === 'string';
   let begin = relativeBegin ?
-    parseTime(options.begin) :
+    parseTime.humanStr(options.begin) :
     Math.max(options.begin - liveBuffer, 0) || 0;
   let liveBegin = Date.now() - liveBuffer;
 

diff --git a/lib/parse-time.js b/lib/parse-time.js
@@ -14,7 +14,7 @@ const timeUnits = {
   m: 60000,
   h: 3600000,
 };
-module.exports = (time) => {
+exports.humanStr = (time) => {
   if (typeof time === 'number') { return time; }
   if (numberFormat.test(time)) { return +time; }
   const firstFormat = timeFormat.exec(time);
@@ -33,3 +33,19 @@ module.exports = (time) => {
     return total;
   }
 };
+
+/**
+ * Parses a duration string in the form of "123.456S", returns milliseconds.
+ *
+ * @param {string} time
+ * @return {number}
+ */
+exports.durationStr = (time) => {
+  let total = 0;
+  const r = /(\d+(?:\.\d+)?)(S|M|H)/g;
+  let rs;
+  while ((rs = r.exec(time)) != null) {
+    total += +rs[1] * timeUnits[rs[2].toLowerCase()];
+  }
+  return total;
+};
diff --git a/test/dash-mpd-parser-test.js b/test/dash-mpd-parser-test.js
@@ -11,12 +11,15 @@ describe('dash MPD parser', () => {
       let items = [];
       let endlist = false;
       const parser = new DashMPDParser();
+      let starttime;
+      parser.on('starttime', a => starttime = a);
       parser.on('item', (item) => { items.push(item); });
       parser.on('endlist', () => { endlist = true; });
       parser.on('error', done);
       let rs = fs.createReadStream(filepath);
       rs.pipe(parser);
       rs.on('end', () => {
+        assert.equal(new Date(starttime).toISOString(), '2018-08-20T16:24:21.942Z');
         assert.ok(!endlist);
         assert.deepEqual(items, [
           { url: 'https://videohost.com/139/0001.ts',

diff --git a/test/parse-time-test.js b/test/parse-time-test.js
@@ -4,21 +4,21 @@ const parseTime = require('../lib/parse-time');
 
 describe('parse-time', () => {
   it('Time format 00:00:00.000', () => {
-    assert.equal(parseTime('25.000'), 25000);
-    assert.equal(parseTime('05:30'), 60000 * 5 + 30000);
-    assert.equal(parseTime('01:05:30'), 60000 * 60 + 60000 * 5 + 30000);
-    assert.equal(parseTime('1:30.123'), 60000 + 30000 + 123);
+    assert.equal(parseTime.humanStr('25.000'), 25000);
+    assert.equal(parseTime.humanStr('05:30'), 60000 * 5 + 30000);
+    assert.equal(parseTime.humanStr('01:05:30'), 60000 * 60 + 60000 * 5 + 30000);
+    assert.equal(parseTime.humanStr('1:30.123'), 60000 + 30000 + 123);
   });
 
   it('Time format 0ms, 0s, 0m, 0h', () => {
-    assert.equal(parseTime('2ms'), 2);
-    assert.equal(parseTime('1m'), 60000);
-    assert.equal(parseTime('1m10s'), 60000 + 10000);
-    assert.equal(parseTime('2hm10s500ms'), 3600000 * 2 + 10000 + 500);
+    assert.equal(parseTime.humanStr('2ms'), 2);
+    assert.equal(parseTime.humanStr('1m'), 60000);
+    assert.equal(parseTime.humanStr('1m10s'), 60000 + 10000);
+    assert.equal(parseTime.humanStr('2hm10s500ms'), 3600000 * 2 + 10000 + 500);
   });
 
   it('No format', () => {
-    assert.equal(parseTime('1000'), 1000);
-    assert.equal(parseTime(200), 200);
+    assert.equal(parseTime.humanStr('1000'), 1000);
+    assert.equal(parseTime.humanStr(200), 200);
   });
 });