Embeds: don't strip `index` parameter in YouTube playlist URLs

[lancewillett]

What I expected to happen:
Copy a YouTube playlist URL and paste it into a blog post, and see the video playback start at the index I chose.

Testing with ​https://www.youtube.com/watch?v=shuRm6PKCVg&index=81&list=PL531A54FA9D00636F

What actually happened:
The video embed works except the playlist starts at the beginning, not the "index" location I chose, as indicated with the index=81 in the embed URL: https://www.youtube.com/watch?v=shuRm6PKCVg&index=81&list=PL531A54FA9D00636F

Embed HTML is as follows:

<iframe width="640" height="360" src="https://www.youtube.com/embed/videoseries?list=PL531A54FA9D00636F" frameborder="0" allowfullscreen=""></iframe>

Note the missing index query parameter.

Steps to repeat:

1. Start a new post, paste in ​https://www.youtube.com/watch?v=shuRm6PKCVg&index=81&list=PL531A54FA9D00636F
2. Publish
3. View post, see playback start at video 1 / 194 instead of 81 / 194 as expected

Notes

Testing with Chrome 36.0 on a MacBook Pro, OS X 10.9.4
WP trunk 4.0-beta3-29445-src with vanilla Twenty Ten theme

[johnbillion]

This is an issue with YouTube's oEmbed response. Here's the oEmbed response for the video you linked above:

{
	"thumbnail_height": 360,
	"type": "video",
	"thumbnail_url": "https:\/\/i.ytimg.com\/vi\/shuRm6PKCVg\/hqdefault.jpg",
	"provider_url": "http:\/\/www.youtube.com\/",
	"html": "\u003ciframe width=\"474\" height=\"267\" src=\"https:\/\/www.youtube.com\/embed\/videoseries?list=PL531A54FA9D00636F\" frameborder=\"0\" allowfullscreen\u003e\u003c\/iframe\u003e",
	"width": 474,
	"provider_name": "YouTube",
	"version": "1.0",
	"height": 267,
	"title": "Side Effects Official Trailer #2 [HD]: Channing Tatum and Rooney Mara",
	"author_name": "ENTV",
	"thumbnail_width": 480,
	"author_url": "http:\/\/www.youtube.com\/user\/ENTV"
}

Note that the URL of the iframe in the html element doesn't contain an index parameter. Best to see if you can report this to YouTube (good luck).

[lancewillett]

Submitted to Google via ​https://developers.google.com/youtube/v3/docs/playlists "Report an Issue" link.