Adding captions support for CBS.com videos

[tmthywynn8]

Request

Add support for downloading the Timed Text subtitles from CBS videos. Though they are not one of the formats supported by Youtube-DL (srt and ass), it can just inform the user that this file will be in its original format.

Current result

Youtube-DL says " has no subtitles":

> python youtube-dl -v --write-pages --list-subs http://www.cbs.com/shows/the-dovekeepers/video/C53AEF08-B010-0AAD-9EA2-6F452AAD1436/the-dovekeepers-part-one-/
[debug] System config: []
[debug] User config: []
[debug] Command-line args: [u'-v', u'--write-pages', u'--list-subs', u'http://www.cbs.com/shows/the-dovekeepers/video/C53AEF08-B010-0AAD-9EA2-6F452AAD1436/the-dovekeepers-part-one-/']
[debug] Encodings: locale cp1252, fs mbcs, out cp437, pref cp1252
[debug] youtube-dl version 2015.07.21
[debug] Python version 2.7.2 - Windows-XP-5.1.2600-SP3
[debug] exe versions: ffmpeg 2.2.3, ffprobe 2.2.3, rtmpdump 2.4
[debug] Proxy map: {}
[CBS] the-dovekeepers-part-one-: Downloading webpage
[CBS] Saving request to the-dovekeepers-part-one-_http_-_www.cbs.com_shows_the-dovekeepers_video_C53AEF08-B010-0AAD-9EA2-6F452AAD1436_the-dovekeepers-part-one-_.dump
[ThePlatform] pLF8YN_N_bh_: Downloading XML
[ThePlatform] Saving request to pLF8YN_N_bh_http_-_link.theplatform.com_s_dJ5BDC_pLF8YN_N_bh_meta.smilformat=smil_mbr=true.dump
[ThePlatform] pLF8YN_N_bh_: Downloading webpage
[ThePlatform] Saving request to pLF8YN_N_bh_http_-_link.theplatform.com_s_dJ5BDC_pLF8YN_N_bh_format=preview.dump
pLF8YN_N_bh_ has no subtitles

Expected result

Youtube-DL should download the Timed Text subtitles.

How to implement

Both XML files contain a pointer to the subtitles (two types?):
pLF8YN_N_bh_http_-_link.theplatform.com_s_dJ5BDC_pLF8YN_N_bh_meta.smilformat=smil_mbr=true.dump
Lines 18, 52, 86, 120, 154, 188, 222, 256: <param name="ClosedCaptionURL" value="http://www.cbsstatic.com/closedcaption/Current/Primetime/DFXP/CBS_DOVEKEEPERS_PT1_CONTENT_CIAN_caption_DFXP.xml"/>
Lines 38, 72, 106, 140, 174, 208, 242, 276: <param name="sMPTE-TTCCURL" value="http://www.cbsstatic.com/closedcaption/Current/Primetime/SMPTE/CBS_DOVEKEEPERS_PT1_CONTENT_CIAN_caption_SMPTE.xml"/>
pLF8YN_N_bh_http_-_link.theplatform.com_s_dJ5BDC_pLF8YN_N_bh_format=preview.dump:
Line 90: "cbs$ClosedCaptionURL": "http://www.cbsstatic.com/closedcaption/Current/Primetime/DFXP/CBS_DOVEKEEPERS_PT1_CONTENT_CIAN_caption_DFXP.xml",
Line 94: "cbs$sMPTE-TTCCURL": "http://www.cbsstatic.com/closedcaption/Current/Primetime/SMPTE/CBS_DOVEKEEPERS_PT1_CONTENT_CIAN_caption_SMPTE.xml",