[youtube] add support for format 278 video-only webm

[sdsucks]

format 278 is 256x144 vp9 video-only webm.

G:>youtube-dl -v -w -c -i -F --youtube-include-dash-manifest -o "F:%(title)s by %(uploader)s.%(ext)s" DZpvgTAHKVM
[debug] System config: []
[debug] User config: []
[debug] Command-line args: ['-v', '-w', '-c', '-i', '-F', '--youtube-include-dash-manifest', '-o', '
F:%(title)s by %(uploader)s.%(ext)s', 'DZpvgTAHKVM']
[debug] Encodings: locale cp949, fs mbcs, out cp949, pref cp949
[debug] youtube-dl version 2014.07.15
[debug] Python version 2.7.5 - Windows-7-6.1.7601-SP1
[debug] Proxy map: {}
[youtube] Setting language
[youtube] DZpvgTAHKVM: Downloading webpage
[youtube] DZpvgTAHKVM: Downloading video info webpage
[youtube] DZpvgTAHKVM: Extracting video information
[youtube] DZpvgTAHKVM: Encrypted signatures detected.
[youtube] encrypted signature length 88 (44.43), itag 22, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 88 (44.43), itag 43, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 88 (44.43), itag 18, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 88 (44.43), itag 5, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 88 (44.43), itag 36, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 88 (44.43), itag 17, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 84 (43.40), itag 138, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 84 (43.40), itag 272, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 84 (43.40), itag 264, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 84 (43.40), itag 271, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 84 (43.40), itag 137, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 84 (43.40), itag 248, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 84 (43.40), itag 136, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 84 (43.40), itag 247, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 84 (43.40), itag 135, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 84 (43.40), itag 244, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 84 (43.40), itag 134, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 84 (43.40), itag 243, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 84 (43.40), itag 133, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 84 (43.40), itag 242, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 84 (43.40), itag 160, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 84 (43.40), itag 140, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 84 (43.40), itag 171, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 88 (44.43), itag 138, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 88 (44.43), itag 272, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 88 (44.43), itag 264, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 88 (44.43), itag 271, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 88 (44.43), itag 137, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 88 (44.43), itag 248, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 88 (44.43), itag 136, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 88 (44.43), itag 247, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 88 (44.43), itag 135, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 88 (44.43), itag 244, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 88 (44.43), itag 134, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 88 (44.43), itag 243, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 88 (44.43), itag 133, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 88 (44.43), itag 242, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 88 (44.43), itag 160, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 88 (44.43), itag 140, html5 player en_US-vflqZIm5b
[youtube] encrypted signature length 88 (44.43), itag 171, html5 player en_US-vflqZIm5b
[youtube] DZpvgTAHKVM: Downloading DASH manifest
[info] Available formats for DZpvgTAHKVM:
format code extension resolution note
139 m4a audio only DASH audio 49k , audio@ 48k (22050Hz), 1.19MiB (worst)
140 m4a audio only DASH audio 129k , audio@128k (44100Hz), 3.17MiB
171 webm audio only DASH audio 131k , audio@ 48k (44100Hz), 3.02MiB
172 webm audio only DASH audio 188k , audio@256k (44100Hz), 4.29MiB
141 m4a audio only DASH audio 255k , audio@256k (44100Hz), 6.29MiB
160 mp4 256x144 DASH video 111k , video only, 2.67MiB
242 webm 426x240 DASH video 283k , video only, 5.20MiB
133 mp4 426x240 DASH video 248k , video only, 6.04MiB
243 webm 640x360 DASH video 524k , video only, 9.59MiB
134 mp4 640x360 DASH video 608k , video only, 14.83MiB
244 webm 854x480 DASH video 798k , video only, 16.29MiB
135 mp4 854x480 DASH video 1112k , video only, 27.26MiB
247 webm 1280x720 DASH video 1751k , video only, 33.22MiB
136 mp4 1280x720 DASH video 2222k , video only, 54.45MiB
248 webm 1920x1080 DASH video 2962k , video only, 53.66MiB
137 mp4 1920x1080 DASH video 4197k , video only, 102.10MiB
264 mp4 1440p DASH video , video only
271 webm 2560x1440 DASH video 25798k , video only, 371.49MiB
272 webm 3840x2160 DASH video 36980k , video only, 651.40MiB
138 mp4 3840x2160 DASH video 25169k , video only, 547.43MiB
278 unknown_video?x256 206k , 2.13MiB
17 3gp 176x144
36 3gp 320x240
5 flv 400x240
43 webm 640x360
18 mp4 640x360
22 mp4 1280x720 (best)