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 640x360 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 800x480 pixel, almost big enough for the standard Youtube PC resolution of 854x480 pixel.