Trying to figure something out. Take a camera that can record 1080P and 720P. Say it's got a codec with a 50mb/sec data rate. If you're shooting a moving subject, or panning or have a scene with a lot of moving details, would you get a better result recording at 720 because the codec is having to process a lot less info and so has less break-up? So it'd be better to shoot 720/25P than 1080/25P in some situations?
Steve

Trying to figure something out. Take a camera that can record 1080P and 720P. Say it's got a codec with a 50mb/sec data rate. If you're shooting a moving subject, or panning or have a scene with a lot of moving details, would you get a better result recording at 720 because the codec is having to process a lot less info and so has less break-up? So it'd be better to shoot 720/25P than 1080/25P in some situations?
Steve

I think the 720p would handle the motion a bit better but not so much more than to give up the extra resolution. I would have to see both videos side by side, but maybe it would be better to shoot in 720p, considering that scenario. But then again if the codec is efficient enough like AVC-intra, I don't think you will see any percieved motion artifacts shooting in either, 1080p or 720p, so I guess I would stick with 1080p.

Take a camera that can record 1080P and 720P. Say it's got a codec with a 50mb/sec data rate. If you're shooting a moving subject, or panning or have a scene with a lot of moving details, would you get a better result recording at 720 because the codec is having to process a lot less info and so has less break-up?

Since you point out that both choices are progressive, the only way that a codec would influence how motion is preserved in the image would be if it was working as temporal compression...like long GOP MPEG or Windows Media. If you had an I-frame codec (no temporal compression), then how motion is captured will have more to do with the camera (aperture, shutter speed, etc...) than the compression.

Now...that's not to say that the choice of framesize has no affect on -overall- image 'quality'...with a fixed data rate, as you point out, the fewer pixels you're handling, the better the image 'quality' (meaning really 'accuracy' I suppose). However motion specifically won't be affected by framesize choice.

I interpreted the OP as refering to a situation where high motion in the scene was leading to compression artifacts. In that case, for a given bitrate yes 720P25 will definitely have less artifacting than 1080P25 option.

If the 1080 is interlaced, the answer is less clearcut, although on balance I would anticipate the 720P would still be preferable.