More accurate indication of current position in file writing graphs

[mikecopperwhite]

IMediaSeeking::GetCurrentPosition called on the filter graph does not give accurate progress information for a file writing graph (see https://msdn.microsoft.com/en-gb/library/windows/desktop/dd407028(v=vs.85).aspx)

For file writing graphs we need to query the current position on the muxer filter.

How to find the 'muxer' filter?

• look at the filters upstream of the file writer.
• manually specify which filter to use for position
• call renderers to see which implement GetCurrentPosition

How to determine if this is a graph where we need to query the muxer for current position?

• Make this an optional behaviour which is selected it manually by the user
• Look for renderer filters that are likely not to report position accurately - e.g. file writer

Perform some tests on graphedit to see what it's doing to get progress for different renderer filters or file writers.

[mikecopperwhite]

One way to achieve this:

Create a property page for filters which is 'IMediaSeeking' which is a limited subset of the find window but calls IMediaSeeking directly on that filter only, not the graph.

This might just be limited to showing the current position - as recommended in the MSDN docs for getting the progress of a file writing graph. Perhaps should initially test this with the Avi Mux filter.