Wednesday, October 6, 2010

Mobile Video Calling: Can Tango Tango?

Tango is a newly launched mobile-to-mobile video calling application for iPhone and Android devices. Tango enables smart-phone owners to see each other in addition to speaking with each other during a Voice Over IP (voip) conversation. Many smart-phones come with front facing cameras, ostensibly for video calling, and Tango enables people to use these cameras during a voip call. Think of mobile video calling when you want to see your expat pet doing silly tricks on video (or for beach and boardroom voyeurism).

But, as Walter Mossberg's Tango's review in WSJ reports, the  quality of Tango's video call leaves a lot to be desired. I came across a video on Gizmodo's website showing Tango in action. The verdict is that Tango's performance is way below expectation. In fact, Tango's video frame-rate seemed to be approximately 1 frame per second in the Gizmodo video (and not the "high quality video mobile calling service" as the company's press release claims).

Make no mistake, achieving even 1 frame-per-second video+voice is no small feat. Tango's engineers have packed a real-time video+voice encoder/decoder into a smart-phone and have managed to trasmit/receive two parallel audio/video streams over Wifi (they also claim high quality video calls over 3G but lets not give Tango all the benefit of doubt :-) ). On top of this, achieving this for both the Android and iPhone platforms and for dozens of smart-phone models is admirable.

Frankly, I am not surprised by Tango's dismal video frame rate - resource bottlenecks such as smart-phone hardware, software/OS, network bandwidth and latency have to be overcome before an acceptable double digit frame-rate is achieved. But what surprised me was the poor voice quality: the Tango call sounded a lot like those cheap international calling cards I used to make international calls from the US  many years ago. Terrible sound quality. I wonder why Tango engineers didn't trade more video quality (or even cut out video entirely when resources were scarce) and spend resources on improving voice? Voice over IP for mobile phones is a solved problem - Skype and the umpteen number of mobile SIP voip clients got audio to work well even on older smart-phones. Why couldn't Tango?

Tango is an over-the-top application, meaning that it runs over the best-effort (ordinary) Internet. I mention this here because the alternative, 3G telecom-operator-supported video calling, uses a dedicated network channel to ensure call quality assurance. But a Tango call will be carried over the same pipes as plain web traffic, making the video/voice call quality dependent on what else is being transmitted during the call. Telecom-supported 3G video calling is also much more energy (battery) efficient  than Tango.Why? Because in order to remain signed-into Tango to receive calls, the smart-phone has to periodically send "I-am-alive" messages to the Tango server. This means that a TCP or UDP socket is always active (or repeatedly created and and torn-down), effectively disabling the smart-phone's built-on power-saving sleep function. Offcourse, telecom supported 3G video calling costs money, but it is technically superior to Tango or any other over-the-top mobile video calling system.

But this is not about Telecom vs. Internet applications. This is about the use-case. Video calling was touted as one of the big use-cases for 3G Telecom networks (and 4G too?). 3G standards support video calling and so there is hardware acceleration, network resource reservation, optimized audio/video codecs, and cross-phone/OS support for video calling on every modern smart-phone. But apart from the cost of making 3G video calls, is their something else that relegated video calling to its sad never-used status in phones? Yes there is. Video calling has simply not been accepted as a viable form of mass communication in our society, and remains to-date, a quirky add-on. When was the last time you  placed a video call?

When Internet telephony (voip) arrived it quickly replaced circuit-switched calling. With mobile video calling, even if Tango can eventually fix its technical/engineering limitations, there is nothing to replace! Sadly, the mobile video calling use-case was still-born from the beginning.

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