Yes, but the screen capture would always be 8bit RGB because that's what PCs are working in - even if the capture is 10bit. And we don't know if the video playback application is using dithering or any other sort of processing. Especially if the source happens to be YCbCr, a screen capture won't do. It might be better to look at the raw uncompressed video stream with a hex editor. When using a full field test pattern, 99.9% of the raw stream should have the exact same byte sequence. So it should be easy enough to figure out the exact YCbCr or RGB data this way.