Conversations – The Data Rate of Voice and Video Calls

So there we go, the Conversations XMPP messaging app has voice and video calls now. A dream come true! Pretty much everyone I used it with so far was stunned by the audio and video quality of the calls. So I was highly interested, of course, to have a closer look at the data rates during audio and video calls.

When audio/video calls are established from behind NAT firewalls, which is usually the case, the user data stream has to traverse my STUN/TURN server so it’s easy to use ‘nload’ or other tools to have a look at the datarates. In case of a Conversations video call, each side sends a video data stream of 2.5 Mbit/s if the bandwidth is available. It seems there is a rate adaption mechanism in place in case this bandwidth is not available, which is sometimes a bit of a problem in the uplink direction for some people. However, I haven’t taken a closer look at that yet.

So in other words, the combined downlink/uplink data rate is 5 Mbit/s on each device. That’s around 1.8 GB of data per hour. Quite a bit of data and not an issue when connected to a fixed line home Wi-Fi. However, for metered cellular connections, it’s a value that needs some consideration. If your monthly data bucket is 5 GB, your video calls and other activities for the month ends after 2.5 hours.

Let’s have a look at a voice call. My TURN server registers 100 kbit/s in each direction, i.e. 50 kbit/s for each voice path. That’s 0.036 GB an hour, i.e. 1/50th of a video call or 125 hours of calling per month with a 5GB monthly cellular data bucket.