Bug 991448 - Skip Theora decode to next keyframe after seek, so that we don't get visual artifacts after a fastSeek. r=cajbir

content/media/ogg/OggReader.cpp

@@ -1379,6 +1379,28 @@ nsresult OggReader::Seek(int64_t aTarget,
     }
   }
 
+  if (HasVideo()) {
+    // Decode forwards until we find the next keyframe. This is required,
+    // as although the seek should finish on a page containing a keyframe,
+    // there may be non-keyframes in the page before the keyframe.
+    // When doing fastSeek we display the first frame after the seek, so
+    // we need to advance the decode to the keyframe otherwise we'll get
+    // visual artifacts in the first frame output after the seek.
+    bool skip = true;
+    while (DecodeVideoFrame(skip, 0) && skip) {
+      ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
+      if (mDecoder->IsShutdown()) {
+        return NS_ERROR_FAILURE;
+      }
+    }
+
+#ifdef DEBUG
+    const VideoData* v = mVideoQueue.PeekFront();
+    if (!v || !v->mKeyframe) {
+      NS_WARNING("Ogg seek didn't end up before a key frame!");
+    }
+#endif
+  }
   return NS_OK;
 }
 

content/media/test/manifest.js

@@ -356,7 +356,10 @@ var gFastSeekTests = [
   { name:"gizmo.mp4", type:"video/mp4", keyframes:[0, 1.0, 2.0, 3.0, 4.0, 5.0 ] },
   // Note: Not all keyframes in the file are actually referenced in the Cues in this file.
   { name:"seek.webm", type:"video/webm", keyframes:[0, 0.8, 1.6, 2.4, 3.2]},
-  // Note: omitting Ogg from this test, as I'm not sure our Ogg seek code is optimal/correct - cpearce
+  // Note: the sync points are the points on both the audio and video streams
+  // before the keyframes. You can't just assume that the keyframes are the sync
+  // points, as the audio required for that sync point may be before the keyframe.
+  { name:"bug516323.indexed.ogv", type:"video/ogg", keyframes:[0, 0.46, 3.06] },
 ];
 
 function IsWindows8OrLater() {