[FFmpeg-user] How do I increase the playback size of a video without rescaling it?

[Chris Wood]

I have a 720x576 video that when played in VLC fills the window
horizontally, so if I maximise the window it effectively fills the display.
When played on TV (via my PS/3) it plays full screen.

I have another video 1280x720 that plays back in a small rectangle, ditto
on the TV. Why? I can use ffmpeg to resize this video to make the image
larger by using the scale function, but this adds pixels by interpolation
and makes the file larger - pointlessly in a way because no new information
is being added that couldn't be added by the video player itself.

This can't be an issue about the lack of pixels, because the 720x576 video
plays back larger than the 1280x720 video. I've experimented with the DAS
and SAR values, which change the shape of the image but not make it bigger.
What am I not understanding?

Chris