CODEWITHSUNDEEP
c++winapivideodirectshow
Christoph
Christoph

Reputation: 2004

Tee/passthrough DirectShow data as video source

I have an application that gets video samples from a frame grabber card via DirectShow. The application then does some processing and sends the video signal over a network. I now want to duplicate this video signal such that another DirectShow-enabled software (like Skype) can use the original input signal, too.

I know that you can create Tee filters in DirectShow like the one used to split a video signal for recording and preview. However, as I understand, this filter is only useful within a single graph, ie I cannot use it to forward the video from my process to eg Skype.

I also know that I could write my own video source, but this would run in the process of the consuming application. The problem is that I cannot put the logic of my original application in such a video source filter.

The only solution I could think of is my application writing the frames to a shared memory block and a video source filter reading it from there. Synchronisation would be done using a shared mutex or so. Could that work? I specifically do not like the synchronisation part?

And more importantly, is there a better solution to solve this problem?

Upvotes: 4

Views: 259

Answers (1)

Roman Ryltsov
Roman Ryltsov

Reputation: 69642

The APIs work as you identified: a video capture application, such as Skype, is requesting video stream without interprocess communication in mind, there is no IPC involved to consume output generated in another process. Your challenge here is to provide this IPC yourself so that one application is generating the data, and then another extends existing API (virtual video source device) and picks existing data, then delivers as generated.

With video, you have a relatively big stream of data and you are interested in avoiding its excessive copying. File mappings (AKA shared memory) are the right thing to do: you put bytes in one process and they are immediately visible in another. You can synchronize access to the data using names events and mutexes which both processes use collaboratively - to signal availability of new buffer of data, as indication that used buffer is no longer in use etc.

Upvotes: 1

Related Questions