Blog/20130624 YouTube bitrates

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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

Type bitrate total size
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.

1.3 Notes

Related articles, discussing similar problems over five years ago(!): Multimedia Encoding Workflow, Multiformat Media Delivery, Video Distribution.


2013-06-24 | Leave a comment | Back to blog