The 840AV's capture rates are (not surprisingly) dependent on several factors, such as amount of compression, level of hard disk fragmentation and the capture resolution. At a full 640x480, you can probably sustain 1-2fps with no post-compression, and perhaps double that with.
Capture rates roughly triple at each reduction in resolution, to 320x240, then to 160x120.
For short bursts, you can do much better, but you'll be limited by the amount of ram. Since you seem to be thinking of using it in RTV mode (Retro TiVo), I suggest 320x240 with post-compression. You might get about 10fps, which will be sort of watchable. If you don't mind postage-stamp sized video, you can do even better at 160x120. It might even permit you to record half-decent audio, too.
And you'll need a very, very big disk.
Capture rates roughly triple at each reduction in resolution, to 320x240, then to 160x120.
For short bursts, you can do much better, but you'll be limited by the amount of ram. Since you seem to be thinking of using it in RTV mode (Retro TiVo), I suggest 320x240 with post-compression. You might get about 10fps, which will be sort of watchable. If you don't mind postage-stamp sized video, you can do even better at 160x120. It might even permit you to record half-decent audio, too.
And you'll need a very, very big disk.