Back in December I reported on some tests I ran to determine the data rates used by Youtube for streaming videos at different resolutions. The result was that a 30 second input file generated with a Nokia N8 of around 45 MB in 720p quality was converted by Youtube into 2.7 MBit/s stream (23 MB total) for a 720p HD stream and to a 1.2 MBit/s stream for the 480p resolution. At the time I assumed that those streams are also used on mobile devices, especially for the new smartphones with a dedicated Youtube client that offer a quite nice looking "HQ" streaming from Youtube.
Recently I revisted the topic and decicded that seeing is better than believing and to trace what was actually going on. To see how the videos are requested I used a Wi-Fi access point and a PC as a gateway to the Internet on which I could run Wireshark to see what is going on. I used three Android based smartphones from three different manufacturers which each had the Google Youtube client installed by default. All of them took the "HQ" (note it's not "HD", it's "HQ", a fine difference…) version of my original video which actually turned out to be in a resolution of 640×360 pixel (i.e. 360p), which is lower than the standard quality for the PC which is 480p. At 30 frames per second the video is streamed at 0.7 MBit/s which translates in about 2.7 MB of data for a 30 second video clip.
By the way: This version of the video can be watched on the PC as well, e.g. with VLC. With Wireshark, the URL of the stream can be copy and pasted over to the web browser which will then download the stream into a file. That file can then be played back and examined with VLC.
0.7 MBit/s is roughly half of the streaming rate of the standard PC resolution and much easier to achieve in life networks under less than ideal coverage conditions compared to the standard or HD resolution streams. Nevertheless, the videos still look very good, even if they need to be upscaled a little bit for current smartphone displays. The Samsung Galaxy S and S-II for example have a screen resolution of 800×480 pixel, almost big enough for the standard Youtube PC resolution of 854×480 pixel.
Many believe that watching an online video with less resolution but without stalling is better than watching a high quality video with constant stalling and buffering. Youtube clients on mobiles seem to be optimized in this way. I remember being able to watch a Youtube video on my N95 using EGPRS. 20 kB/s was enough to watch videos on that mobile, although it needed some time to buffer and start playing the video.
I think that optimizing applications is as important as providing enough bandwidth for wireless broadband. Mobile operators just wouldn’t be able to provide bandwidth for ever growing demand for data without optimizing users’ consumption. Opera browser is another example of such optimization.
By the way, one thing that hasn’t been mention is that Youtube clients don’t download the whole video you’re watching, at least on Nokia N97 that I own. When you watch a video you see a circular button moving and indicating where the video is playing and the partly transparent strip shows how much of the video has been downloaded. When using a youtube client on a mobile the transparent strip moves only about a dozen of seconds ahead and when the video is paused the transparent strip stops too. This must have been done to prevent downloading the whole video and to conserve data in case a user doesn’t want to watch the whole video or just browsing Youtube videos in order to find something worthy their attention. It’s very wise move in my eyes. On the opposite, a browser on a PC downloads the whole video even if when paused.
Interesting, recently I did my own test to see what is the data throughput requirement for YouTube HQ video on mobile network. On a SonyEricsson Xperia Arc handset, I am seeing that YouTube HQ video is generally streamed at 1.3 mbps. Perhaps because the screen native resolution on handset in 854×480.