[Generic] Check iframes for known file extensions

[johnhawkinson]

As discussed in #12692, this is the easy option, 1.:

1. Check file extension of iframes for ../utils/KNOWN_EXTENSIONS. (This could happen fairly early in GenericIE)

Since Sergey said

By default only 1 can be applied.

Unfortunately, between then and now(*), the test case I had updated to point to a Youtube video, and I don't have a test case for the direct iframe link. I searched https://publicwww.com/ and didn't come up with anything. I guess they're not common.

So I don't know if this is worth committing without a test. It works against my local webserver with the iframe from yesterday inserted:

<iframe height="360" width="640"
      src="https://cdn-e2.streamable.com/video/mp4/wfatk.mp4?token=1492919903_c3707bc86745b37c149c2be0da56b98a275b2b74"
    >
    </iframe>

Or I could add a test to test_InfoExtractor.py?

---

(*) I suppose maybe it's fortunate that it happened so quickly, rather than happening next week after this was committed and breaking the test case while no one was watching.

[johnhawkinson]

fyi, VF has another of these tonight

http://www.vanityfair.com/hollywood/2017/04/snl-melissa-mccarthy-sean-spicer-easter-bunny-hitler

which has

<div
  class="embed iframe-embed-component "
  data-type="iframe"
  data-url="https://cdn-e2.streamable.com/video/mp4/wb4dr.mp4?token=1493525991_6e4d1806902118fba090b4e528109b806e5d8c4d"
>
  <iframe
    height="360" width="640"
    src="https://cdn-e2.streamable.com/video/mp4/wb4dr.mp4?token=1493525991_6e4d1806902118fba090b4e528109b806e5d8c4d"
  >
  </iframe>
</div>

And this code properly works against it.

I imagine they'll replace it with a Youtube link when SNL posts their youtube stuff, though, like last week…