RaP: Workaround broken seeking in flv after red5 update.

Since the update to the newer red5, seeking in flv files (webcams in
particular are noticable) has been broken, resulting in cameras
appearing to "hang" any time there is a cut in the generated video -
which happens when start/stop button is pushed, or when cameras are
added or removed.

We can detect the problematic video files because the timestamp of the
first frame is large (old red5 versions always set first frame
timestamp to 0.001 seconds). If we see a file like this, having ffmpeg
remux the file - rewriting the timestamps and index - works around the
problem.

record-and-playback/core/lib/recordandplayback/edl/video.rb

@@ -171,6 +171,7 @@ module BigBlueButton
         videoinfo = {}
 
         corrupt_videos = Set.new
+        remux_flv_videos = Set.new
 
         BigBlueButton.logger.info "Pre-processing EDL"
         for i in 0...(edl.length - 1)
@@ -196,12 +197,50 @@ module BigBlueButton
             BigBlueButton.logger.debug "    width: #{info[:width]}, height: #{info[:height]}, duration: #{info[:duration]}, start_time: #{info[:start_time]}"
             if info[:video][:deskshare_timestamp_bug]
               BigBlueButton.logger.debug("    has early 1.1 deskshare timestamp bug")
+            elsif info[:format][:format_name] == 'flv' and info[:start_time] > Rational(1,1000)
+              BigBlueButton.logger.debug("    has large start time, needs remuxing")
+              remux_flv_videos << videofile
             end
           end
 
           videoinfo[videofile] = info
         end
 
+        if remux_flv_videos.length > 0
+          BigBlueButton.logger.info("Remuxing flv files with large start time")
+          remux_flv_videos.each do |videofile|
+            BigBlueButton.logger.info("  #{File.basename(videofile)}")
+            newvideofile = File.join(File.dirname(output_basename), File.basename(videofile))
+
+            if !File.exist?(newvideofile)
+              ffmpeg_cmd = [*FFMPEG]
+              ffmpeg_cmd += ['-i', videofile, '-c', 'copy', newvideofile]
+
+              exitstatus = BigBlueButton.exec_ret(*ffmpeg_cmd)
+              raise "ffmpeg failed, exit code #{exitstatus}" if exitstatus != 0
+            end
+
+            info = video_info(newvideofile)
+            if !info[:video]
+              BigBlueButton.logger.warn("    Result of remux is corrupt, not using it.")
+              next
+            end
+            BigBlueButton.logger.debug "    width: #{info[:width]}, height: #{info[:height]}, duration: #{info[:duration]}, start_time: #{info[:start_time]}"
+            videoinfo[newvideofile] = info
+
+            # Update the filename in the EDL
+            edl.each do |event|
+              event[:areas].each do |area, videos|
+                videos.each do |video|
+                  if video[:filename] == videofile
+                    video[:filename] = newvideofile
+                  end
+                end
+              end
+            end
+          end
+        end
+
         if corrupt_videos.length > 0
           BigBlueButton.logger.info "Removing corrupt video files from EDL"
           edl.each do |event|
@@ -389,7 +428,7 @@ module BigBlueButton
             BigBlueButton.logger.debug "      offset: left: #{offset_x}, top: #{offset_y}"
 
             BigBlueButton.logger.debug("      start timestamp: #{video[:timestamp]}")
-            seek_offset = this_videoinfo[:video][:start_time]
+            seek_offset = this_videoinfo[:start_time]
             BigBlueButton.logger.debug("      seek offset: #{seek_offset}")
             BigBlueButton.logger.debug("      codec: #{this_videoinfo[:video][:codec_name].inspect}")
             BigBlueButton.logger.debug("      duration: #{this_videoinfo[:duration]}, original duration: #{video[:original_duration]}")