For the moment, what do you need for frames -> seconds? Both PAL and NTSC? Are there others?
From what I remember about analog video standards, SECAM was the third. There are variations on those, also, it seems. This page
has some detail (I googled SECAM... whee) regarding those standards. Specifically, charts on the page showing, for each standard, the lines per field, horizontal/vertical frequencies, color subcarrier frequency (for PAL and NTSC), sound carrier frequency, and video bandwidth.
Other links on the site provide interesting info, but other/better (?) sources for the conversion data are probably easily found. That site seems to want to charge for the service of performing video conversions between standards and I tend to be suspicious of commercial sites
hiding behind pretending to be
embedded within informative sites. A personal problem of mine, perhaps.
In other words: If you add those conversions, to ensure accuracy, you might want to cross-reference the information provided there (or wherever you obtain it) with information from other sources.