directshow mpeg2 text overlay without decoding

Question

I found some directshow filters that does text overlay, but they always build this graph:

source mpeg2 (only video) -> mpeg2 decoder -> overlay -> (some encoder) ... -> file writer

Is possible (also with a third party filter), in directshow, to build a text overlay without decode the mpeg2 stream?

source mpeg2 (only video) -> overlay -> file writer

Because the encoding process is very cpu critical (I have to process about 6 or 8 video in real time) and writing decoded files without compression takes about 170 MB (320x240) every 2 minutes per file.

Thanks

Answer 1

You can't get the overlay burned in to the video without decoding the video first. But you could have a text stream in the file, which was rendered and overlaid at playback time. A custom filter for decoding would be the easiest, and you would implement IStreamBuilder on the custom filter's output pin to connect it to a VMR secondary input when building the graph. Or you could encode it in a recognised caption format, and then choose a player that supports that format.

G