Weird substance on top of beer

i bottled a stout about 17 days ago and about two days after bottling i noticed a film (white, maybe 1 mm thick) at the neckline of almost each bottle. thought that i had an infection, but was willing to wait it out and see how it turned out. today i checked and the film, while still present, is very faint.
could it have been yeast?
i am chilling a couple bottles now to test the taste of the beer. more on that later.

Don't worry. I'm sure it's just a mini krausen ring from the fermentation that took place in the bottles. It's fairly common.

well, after a taste test on two bottles, it seems i worried for nothing. the beer tastes fine, unremarkable in every aspect, just as i would expect "green" beer to taste. i believe that after several weeks in the bottle it will become a good stout.

I had the same thing one time. I knew mine was a mold as the FG was finished, but the mold kept growing (from 3-4 weeks into the secondary). The stuff mostly dissapated when bottling. It reminded me of white pond scum. My bottles had some in the neck, but it died from the CO2. Papazian said something like this was from an infection - however, my beer turned out great.

Just make extra sure to clean all the equipment that came into contact with the beer (including the bottles).

You should be fine.

Cheers.