Of those sentances the one with "in" looks the most idomatic to me. However.
640p refers to the pixel count width wise.
When talking about video the number before the p or i (BTW p is short for progressive not for pixels) refers to the vertical resolution, not horizontal. 640p is not a common/standard resolution. The normal values are.
- 240p: half NTSC
- 480i: NTSC (interlaced)
- 480p: same as NTSC resoloution but progressive scan, also sometimes known as "VGA".
- 576i: PAL (interlaced)
- 576p: PAL resoloution but progressive scan.
- 720p and 1080i: "HD ready".
- 1080p: full HD
The corresponding horizontal resolution is less-well defined. Traditionally analog video was not formed of pixels, the video was split into discrete "lines" but the variations within each line were a continuous analog signal.
Digital systems clearly do have pixels but the number varies. On a square-pixel system it will depend on the aspect ratio (4:3 or 16:9) but there are also "Anamorphic widescreen" systems with non-square pixels.