nix youtube enclosure in rss feed

[willkg]

For videos that are hosted on YouTube, we'd also include the YouTube video url in the enclosure list in the RSS feed because Miro was able to use that and download the video.

Miro is essentially dead, now. I don't know of any other rss clients that work with YouTube video links.

Given that, we should nix the special case enclosure.

[codersquid]

I use NewsBlur as an rss client, and I've seen posts that render with youtube videos. I'll try to dig up an example to see if it is something we can do.

[willkg]

So I think I want to make the following changes:

1. nix the youtube-specific code in the RSS enclosures--no more youtube links there
2. the description of an rss item should include a list of all the urls associated with the item: source url, all media urls, all related urls
3. (related to rss feeds not being "valid") we should fix the enclosure metadata particularly fileSize, type and length

I want to tackle items 1 and 2 in this issue and tackle item 3 in issue #196 because there's additional data we need to collect in order to do that correctly.