Correct video file timestamping issues

src/VideoStreaming/VideoReceiver.cc

@@ -674,6 +674,14 @@ VideoReceiver::startRecording(const QString &videoFile)
     gst_element_sync_state_with_parent(_sink->mux);
     gst_element_sync_state_with_parent(_sink->filesink);
 
+    // Install a probe on the recording branch to drop buffers until we hit our first keyframe
+    // When we hit our first keyframe, we can offset the timestamps appropriately according to the first keyframe time
+    // This will ensure the first frame is a keyframe at t=0, and decoding can begin immediately on playback
+    GstPad* probepad = gst_element_get_static_pad(_sink->queue, "src");
+    gst_pad_add_probe(probepad, (GstPadProbeType)(GST_PAD_PROBE_TYPE_BUFFER /* | GST_PAD_PROBE_TYPE_BLOCK */), _keyframeWatch, this, NULL); // to drop the buffer or to block the buffer?
+    gst_object_unref(probepad);
+
+    // Link the recording branch to the pipeline
     GstPad* sinkpad = gst_element_get_static_pad(_sink->queue, "sink");
     gst_pad_link(_sink->teepad, sinkpad);
     gst_object_unref(sinkpad);
@@ -802,6 +810,33 @@ VideoReceiver::_unlinkCallBack(GstPad* pad, GstPadProbeInfo* info, gpointer user
 }
 #endif
 
+//-----------------------------------------------------------------------------
+#if defined(QGC_GST_STREAMING)
+GstPadProbeReturn
+VideoReceiver::_keyframeWatch(GstPad* pad, GstPadProbeInfo* info, gpointer user_data)
+{
+    Q_UNUSED(pad);
+    if(info != NULL && user_data != NULL) {
+        GstBuffer* buf = gst_pad_probe_info_get_buffer(info);
+        if(GST_BUFFER_FLAG_IS_SET(buf, GST_BUFFER_FLAG_DELTA_UNIT)) { // wait for a keyframe
+            return GST_PAD_PROBE_DROP;
+        } else {
+            VideoReceiver* pThis = (VideoReceiver*)user_data;
+            // reset the clock
+            GstClock* clock = gst_pipeline_get_pipeline_clock(GST_PIPELINE(pThis->_pipeline));
+            GstClockTime time = gst_clock_get_time(clock);
+            gst_object_unref(clock);
+            gst_element_set_base_time(pThis->_pipeline, time); // offset pipeline timestamps to start at zero again
+            buf->dts = 0; // The offset will not apply to this current buffer, our first frame, timestamp is zero
+            buf->pts = 0;
+            qCDebug(VideoReceiverLog) << "Got keyframe, stop dropping buffers";
+        }
+    }
+
+    return GST_PAD_PROBE_REMOVE;
+}
+#endif
+
 //-----------------------------------------------------------------------------
 void
 VideoReceiver::_updateTimer()

src/VideoStreaming/VideoReceiver.h

@@ -119,6 +119,7 @@ private:
 
     static gboolean             _onBusMessage           (GstBus* bus, GstMessage* message, gpointer user_data);
     static GstPadProbeReturn    _unlinkCallBack         (GstPad* pad, GstPadProbeInfo* info, gpointer user_data);
+    static GstPadProbeReturn    _keyframeWatch          (GstPad* pad, GstPadProbeInfo* info, gpointer user_data);
     void                        _detachRecordingBranch  (GstPadProbeInfo* info);
     void                        _shutdownRecordingBranch();
     void                        _shutdownPipeline       ();