[youtube] add filesize extraction for f264

[sdsucks]

filesize extraction works for all DASH formats except f264

G:>youtube-dl -v -w -c -i -F --youtube-include-dash-manifest Cu6YksbZ3cs
[debug] System config: []
[debug] User config: []
[debug] Command-line args: ['-v', '-w', '-c', '-i', '-F', '--youtube-include-dash-manifest', 'Cu6Yks
bZ3cs']
[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] Cu6YksbZ3cs: Downloading webpage
[youtube] Cu6YksbZ3cs: Downloading video info webpage
[youtube] Cu6YksbZ3cs: Extracting video information
[youtube] Cu6YksbZ3cs: Downloading DASH manifest
[info] Available formats for Cu6YksbZ3cs:
format code extension resolution note
139 m4a audio only DASH audio 49k , audio@ 48k (22050Hz), 1.28MiB (worst)
140 m4a audio only DASH audio 129k , audio@128k (44100Hz), 3.42MiB
171 webm audio only DASH audio 138k , audio@ 48k (44100Hz), 3.54MiB
172 webm audio only DASH audio 200k , audio@256k (44100Hz), 5.14MiB
141 m4a audio only DASH audio 255k , audio@256k (44100Hz), 6.78MiB
160 mp4 256x144 DASH video 112k , video only, 2.89MiB
242 webm 426x240 DASH video 172k , video only, 3.98MiB
133 mp4 426x240 DASH video 247k , video only, 6.50MiB
243 webm 640x360 DASH video 328k , video only, 7.47MiB
134 mp4 640x360 DASH video 611k , video only, 12.02MiB
244 webm 854x480 DASH video 648k , video only, 14.67MiB
135 mp4 854x480 DASH video 1120k , video only, 25.33MiB
247 webm 1280x720 DASH video 1239k , video only, 28.70MiB
136 mp4 1280x720 DASH video 2243k , video only, 48.26MiB
248 webm 1920x1080 DASH video 1941k , video only, 45.80MiB
137 mp4 1920x1080 DASH video 4285k , video only, 94.51MiB
264 mp4 1440p DASH video , video only
271 webm 2560x1440 DASH video 9659k , video only, 170.91MiB
272 webm 3840x2160 DASH video 21648k , video only, 330.91MiB
138 mp4 3840x2160 DASH video 25010k , video only, 420.25MiB
278 unknown_video?x256 137k , 2.01MiB
17 3gp 176x144
36 3gp 320x240
5 flv 400x240
43 webm 640x360
18 mp4 640x360
22 mp4 1280x720 (best)