Also, do I understand correctly that the videos as uploaded to YouTube are 1920x1080? It would be nice to have them uploaded on archive.org (or directly Wikimedia Commons https://commons.wikimedia.org/wiki/Category:Wikimania_2014_presentation_vide... if you're able to convert to appropriate formats), because it seems 1280x720 is the best one can download directly.
When the labels are ok, I can easily upload everything on archive.org, but I won't be download the 1920x1080 videos and the audio separately to merge them.
Nemo
$ youtube-dl -F 'https://www.youtube.com/watch?v=D5GKyKujsnM&l' [youtube] Confirming age [youtube] D5GKyKujsnM: Downloading webpage [youtube] D5GKyKujsnM: Downloading video info webpage [youtube] D5GKyKujsnM: Extracting video information [youtube] D5GKyKujsnM: Downloading DASH manifest [info] Available formats for D5GKyKujsnM: format code extension resolution note 139 m4a audio only DASH audio 54k , audio@ 48k (22050Hz), 35.58MiB (worst) 140 m4a audio only DASH audio 134k , audio@128k (44100Hz), 94.69MiB 141 m4a audio only DASH audio 261k , audio@256k (44100Hz), 188.05MiB 160 mp4 256x144 DASH video 135k , video only, 76.23MiB 133 mp4 426x240 DASH video 269k , video only, 180.22MiB 134 mp4 640x360 DASH video 311k , video only, 96.32MiB 135 mp4 854x480 DASH video 635k , video only, 245.35MiB 136 mp4 1280x720 DASH video 1358k , video only, 705.61MiB 137 mp4 1920x1080 DASH video 4111k , video only, 1.65GiB 17 3gp 176x144 36 3gp 320x240 5 flv 400x240 18 mp4 640x360 43 webm 640x360 22 mp4 1280x720 (best)