From dfe834c6ad70f04d9fe1deb4e250af385da833c2 Mon Sep 17 00:00:00 2001
From: birme <jonas.birme@eyevinn.se>
Date: Tue, 19 Jan 2021 15:01:32 +0100
Subject: [PATCH] Added a function to get delta times for each media sequence

---
 index.js            | 27 ++++++++++++++++++++++++++-
 spec/hlsvod_spec.js | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/index.js b/index.js
index d56c74f..f3d51fd 100644
--- a/index.js
+++ b/index.js
@@ -32,6 +32,7 @@ class HLSVod {
     this.discontinuities = {};
     this.rangeMetadata = null;
     this.matchedBandwidths = {};
+    this.deltaTimes = [];
   }
 
   toJSON() {
@@ -51,7 +52,8 @@ class HLSVod {
       startTimeOffset: this.startTimeOffset,
       usageProfileMapping: this.usageProfileMapping,
       usageProfileMappingRev: this.usageProfileMappingRev,
-      discontinuities: this.discontinuities
+      discontinuities: this.discontinuities,
+      deltaTimes: this.deltaTimes,
     };
     return JSON.stringify(serialized);
   }
@@ -78,6 +80,7 @@ class HLSVod {
     this.usageProfileMapping = de.usageProfileMapping;
     this.usageProfileMappingRev = de.usageProfileMappingRev;
     this.discontinuities = de.discontinuities;
+    this.deltaTimes = de.deltaTimes;
   }
 
   /**
@@ -427,6 +430,16 @@ class HLSVod {
     return this.discontinuities[this.mediaSequences.length - 1];
   }
 
+  /**
+   * Get the delta times for each media sequence. 
+   * Returns the sum of the segments' duration for each media sequence and the diff to the previous
+   * media sequence. E.g. [ 0, 2, 2, -2, ... ] means that the second media sequence is 2 second longer
+   * than the first one. The fourth one is 2 seconds shorter than the previous media sequence
+   * 
+   */
+  getDeltaTimes() {
+    return this.deltaTimes.map(o => o.interval);
+  }
 
   // ----- PRIVATE METHODS BELOW ----
 
@@ -613,6 +626,10 @@ class HLSVod {
         reject('Failed to init media sequences');
       } else {
         let discSeqNo = 0;
+        this.deltaTimes.push({
+          interval: 0,
+        });
+        let lastMseqSum = 0;
         for (let seqNo = 0; seqNo < this.mediaSequences.length; seqNo++) {
           const mseq = this.mediaSequences[seqNo];
           const bwIdx = Object.keys(mseq.segments)[0];
@@ -622,6 +639,14 @@ class HLSVod {
             debug(`Increasing discont sequence ${discSeqNo}`);
           }
           this.discontinuities[seqNo] = discSeqNo;
+          const mseqSum = mseq.segments[bwIdx] ? mseq.segments[bwIdx].map(o => o.duration ? o.duration : 0).reduce((acc, curr) => acc + curr, 0) : 0;
+          if (seqNo > 0) {
+            const interval = mseqSum - lastMseqSum;
+            this.deltaTimes.push({
+              interval: interval,
+            });
+          }
+          lastMseqSum = mseqSum;
         }
         resolve();
       }
diff --git a/spec/hlsvod_spec.js b/spec/hlsvod_spec.js
index 33705ff..7987d1b 100644
--- a/spec/hlsvod_spec.js
+++ b/spec/hlsvod_spec.js
@@ -1515,3 +1515,37 @@ describe("HLSVod time metadata", () => {
     });
   });
 });
+
+describe("HLSVod delta time", () => {
+  let mockMasterManifest;
+  let mockMediaManifest;
+
+  beforeEach(() => {
+    mockMasterManifest = function() {
+      return fs.createReadStream('testvectors/hls1/master.m3u8');
+    };
+    
+    mockMediaManifest = function(bandwidth) {
+      return fs.createReadStream('testvectors/hls1/' + bandwidth + '.m3u8');
+    };
+  });
+
+  it("is calculated and available for each media sequence", done => {
+    mockVod = new HLSVod('http://mock.com/mock.m3u8');
+    mockVod2 = new HLSVod('http://mock.com/mock2.m3u8');
+    mockVod.load(mockMasterManifest, mockMediaManifest)
+    .then(() => {
+      return mockVod2.loadAfter(mockVod, mockMasterManifest, mockMediaManifest);
+    }).then(() => {
+      let mockVod2Durations = [];
+      for (let i = 0; i < mockVod2.getLiveMediaSequencesCount(); i++) {
+        mockVod2Durations.push(mockVod2.getLiveMediaSequenceSegments(i)['1497000']
+          .map(o => o.duration ? o.duration : 0).reduce((acc, dur) => acc + dur, 0));
+      }
+      const deltas2 = mockVod2.getDeltaTimes();
+      expect(mockVod2Durations.slice(0, 9)).toEqual([ 51.266, 51.266, 51.266, 51.266, 51.266, 54, 54, 54, 54 ]);
+      expect(deltas2.slice(0, 9)).toEqual([ 0, 0, 0, 0, 0, 2.7340000000000018, 0, 0, 0 ]);
+      done();
+    })
+  });
+});
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