A normal VHS encodes about 100 million scan lines over 2 hours. 20 bytes per scan line sounds feasible, since there's somewhere around 200-300 'pixels' of luma available in each scan line.
Thanks, that's a very reasonable back of the envelope calculation.
There are many fun details about VHS, its chroma resolution, and especially some weirdness around the PAL delay line, but they all don't really matter for this.
Wikipedia says there is about 3MHz of bandwidth, so ~200-300 "pixels" seems like a very good ballpark (just going by the fact that a normal PAL signal has about 6 MHz and is commonly digitized as 720x576, 3MHz about halves the horizontal resolution and taking some pixels off for various reasons makes sense).
