GMFBridge DirectShow filter SetLiveTiming effect

Question

I am using the excellent GMFBridge directshow family of filters to great effect, allowing me to close a video recording graph and open a new one, with no data-loss.

My original source graph was capturing live video from standard video and audio inputs.

There is an undocumented method on the GMFBridgeController filter named SetLiveTiming(). From the name, I figured that this should be set to true if we are capturing from a Live graph (not from a file) as is my case. I set this value to true and everything worked as expected

The same capture hardware allows me to capture live TV signals (ATSC in my case), so I created a new version of the graph using the BDA architecture filters, for tuning purposes. Once the data flows out from the MPEG demuxer, the rest of the graph is virtually the same as my original graph.

However, on this ocassion my muxing graph (on the other side of the bridge) was not working. Data flowed from the BridgeSource filter (video and audio) and reached an MP4 muxer filter, however no data was flowing from the muxer output feeding a FileWriter filter.

After several hours I traced the problem to the SetLiveTiming() setting. I turned it off and everything began working as expected. and the muxer filter began producing an output file, however, the audio was not synchronized to the video.

Can someone enlighten me on the real purpose of the SetLiveTiming() setting and perhaps, why one graph works with the setting enabled, while the other fails?

UPDATE

I managed to compile the GMFBridge Project, and it seems that the filter is dropping every received sample because of a negative timestamp computation. However I am completely baffled at the results I am seeing after enabling the filter log.

UPDATE 2: The dropped samples were introduced by the way I launched the secondary (muxer) graph. I inspected a sample using a SampleGrabber (thus inside a streaming thread) as a trigger-point and used a Task.Run() .NET call to instantiate the muxer graph. This somehow messed up the clocks and I ended having a 'reference start point' in the future - when the bridge attempted to fix the timestamp by subtracting the reference start point, it produced a negative timestamp - once I corrected this and spawned the graph from the application thread (by posting a graph event), the problem was fixed.

Unfortunately, my multiplexed video (regardless of the SetLiveTiming() setting) is still out of sync.

I read that the GMFBridge filter can have trouble when the InfTee filter is being used, however, I think that my graph shouldn't have this problem, as no instance of the InfTee filter is directly connected to the bridge sink.

Here is my current source graph:

                                                                   -->[TIF]
                                                                  |
 [NetworkProvider]-->[DigitalTuner]-->[DigitalCapture]-->[demux]--|-->[Mpeg Tables]
                                                                  |
                                                                  |-->[lavAudioDec]-->[tee]-->[audioConvert]-->[sampleGrabber]-->[NULL]
                                                                  |                        |
                                                                  |                        |
                                                                  |                         ->[aacEncoder]----------------
                                                                  |                                                       |--->[*Bridge Sink*]
                                                                   -->[VideoDecoder]-->[sampleGrabber]-->[x264Enc]--------

Here is my muxer graph:

                      video  
 ...  |bridge source|-------->[MP4 muxer]--->[fileWriter]
             |                     ^
             |        audio        |
              ---------------------

All the sample grabbers in the graph are read-only. If I mux the output file without bridging (by placing the muxer on the capture graph), the output file remains in sync, (this ended being not true, the out-of-sync problem was introduced by a latency setting in the H264 encoder) but then I can't avoid losing some seconds between releasing the current capture graph, and running the new one (with the updated file name)

UPDATE 3:

The out of sync problem was inadvertently introduced by me several days ago, when I switched off a "Zero-latency" setting in the x264vfw encoder. I hadn't noticed that this setting had desynchronized my already-working graphs too and I was blaming the bridge filter.

In summary, I screwed up things by:

1. Launching the muxer graph from a thread other than the Application thread (the thread processing the graph's event loop).

2. A latency switch in an upstream filter that was probably delaying things too much for the muxer to be able to keep-up.

Answer 1

Author's comment:

// using this option, you can share a common clock 
// and avoid any time mapping (essential if audio is in mux graph)
[id(13), helpstring("Live Timing option")]
HRESULT SetLiveTiming([in] BOOL bIsLiveTiming);

The method enables a special mode of operation which addresses live data. In this mode sample times are converted between the graphs as relative to respective clock start times. Otherwise, the default mode is to expect reset of time stamps to zero with graph changes.