Video file to MediaCapture Stream conversion (using WinRT APIs)

Question

MediaCapture class can get stream from physical devices only. My algorithm Flow is somewhat like this;

1. open a video file or picture file (Done)
2. assign it to a (MediaCapture)stream (Help required)
3. process the stream (Done)
4. Write the stream to video file using StartRecordtoStorageFileAsync(parameters)(Done)

So far I am unable to assign a video/picture object to a stream so that i can write it to a video file after processing. Thanks for help!step 4 is assumed to be done only if input stream is available from step 2!