Blog/20130624 YouTube bitrates
1 YouTube bitrates - for your consideration
So we're here at the Opencast Unconference / Diverse 2013, and there's a two things in particular that have made me think about bandwidths and video bitrates again. (Access to OER has been an important topic, see Publications, e.g. the Access 2 OER report, or Bridging the Bandwidth Gap - OER and the Digital Divide.)
I was trying to watch Bob Moon's excellent talk "Educating Teachers in Developing World Contexts: The imperative for radical reform", available here http://sms.cam.ac.uk/media/1476758. The available formats are
|MPEG-4 Video||1024x576||1.93 Mbits/sec||719.83 MB|
|WebM||1024x576||1.57 Mbits/sec||585.28 MB|
|MP3||249.75 kbits/sec||90.64 MB|
|MP3||124.75 kbits/sec||45.32 MB|
|MP3||62.2 kbits/sec||22.66 MB|
Somehow the lowest bitrate video is 1.5 Mb/s? My connection (in a remote, but not-so-remote area in Germany) has about 220kb/s, so no chance of seeing that video. The audio versions are a saver here (and the introduction of audio-only versions of video was due to my relentless campaigning). The connection at the University of Applied Sciences Osnabrück was about 5 Mb/s, so enough bandwidth to watch this. However, this talk is mainly slides, so, um, 1.5 Mb/s?
The second thing that happened was that apparently the multi-format workflows were removed from Opencast Matterhorn. (Do correct me if I got this wrong.)
1.1 YouTube bitrates
So a quick experiment, to provide some more data: I had a quick look at the bitrates of a YouTube video, and these were:
|Resolution||frames per sec||bitrate||format (container, codec)||size||YouTube itag code|
|144p||12fps||80 kb/s||(3gp, mpeg4)||317 kB||itag=17|
|240p||24fps||350 kb/s||(flv, flv1)||1.4 MB|
|360p||24fps||520 kb/s||(mp4, H264)||2 MB||itag=18|
|360p||24fps||520 kb/s||(flv, H264)||2 MB|
|480p||24fps||830 kb/s||(flv, H264)||2.9 MB|
|720p||24fps||1.6 Mb/s||(mp4, H264)||6.3 MB|
|1080p||24fps||3 Mb/s||(mp4, H264)||12.4 MB|
(Those aren't necessarily accurate, as for adaptive encoding they will vary with the type of video content. But these were for normal motion content. In fact for an advertisement featuring Beyoncé.) (Also see Wikipedia on YouTube, Quality_and_codecs.)
1.2 Some questions, left as an exercise
So here's a question for consideration (left as an exercise for the reader, in an enquiry-based way):
Why would YouTube bother creating all these different formats? It's a massive site, with a massive number of videos being added all the time, a massive load on the servers? Surely it would be much easier to just use one format, say 720p video at 1.5 Mb/s, and be done with it? So why does YouTube bother?
Follow-up question: Having answered the previous question, what are the implication for other streaming services?
Invitation to discuss via twitter: https://twitter.com/bjoernhassler/status/349271480133099520.
2013-06-24 | Back to blog|