DirectShow filter graph using WMASFWriter creates video which is too short

2
votes

I am attempting to create a DirectShow source filter based on the pushsource example from the DirectShow SDK. This essentially outputs a set of bitmaps to a video. I have set up a filter graph which uses Async_reader with a Wave Parser for audio and my new filter to push the video (the filter is a CSourceStream and I populate my frames in the FillBuffer function). These are both connected to a WMASFWriter to output a WMV.

Each bitmap can last for several seconds so in the FillBuffer function I'm calling SetTime on the passed IMediaSample with a start and end time several seconds apart. This works fine when rendering to the screen but writing to disk results in a file which is too short in duration. It seems like the last bitmap is being ignored when writing a WMV (it is shown as the video ends rather than lasting for the intended duration). This is the case both with my filter and a modified pushsource filter (in which the frame length has been increased).

I've seen additional odd behaviour in that it was not possible to have a video that wasn't a multiple of 10 seconds in length at one point whilst I was trying to make this work. I'm not sure what this was, but I though I'd mention it incase it's relevant.

1
c++directshow

1 Answers

1
votes

I think the end time is simply ignored. Normally video samples only have a start time because they are a point in time. If there is movement in the video, the movement is fluent, though the video are just points in time.

I think the solution is simple. Because video stays the same until the next frame is received, you can just add a dummy frame at the end of your video. You can simply repeat the previous frame.