counters - Why are movies/video-clips counted with 本?

I just noticed in my Facebook uploads that for my videos, it says I have 25本. What's the reasoning behind using 〜本 to count videos or movie clips? The only line of reasoning I can come up with would be thinking of the the movies as as old reel of actual film

    

Even though they are circular, they are more flat than long, so I would think those would be counted as 〜枚 instead of 〜本.

So what's the reasoning for using 〜本?

Answer

A good resource for this type of question is 『数え方の辞典』. It includes the following:

映画の作品数・上映数は「本」で数えます。細長い映画のフィルムが、巻かれた状態でひとつの作品として扱われることに由来します。

There is further information on various cases when it may be counted as 作, 作品, 巻き, 巻 (kan), 齣 (koma), カット, シーン, 場面 etc. For more details, I recommend consulting this at a library or getting your own copy.