Streaming Over 4G with Teradek Cube, Pt. 2: Testing Results

In Part 1 of this article, we looked at how to set up a live webcast over 4G with the Teradek Cube and the Bond 4G Cellular Transmitter. Now we'll look at the results of my testing with the setup we assembled.

Low-Bitrate Testing

In testing from my office, the outbound bitrate was limited to about 800 Kbps total, so I tested at 848x480 (480p) at 500 Kbps video and 48 Kbps audio. This is a bits-per-pixel value of around 0.04, which is way low; in contrast, ESPN's 768x432 stream is encoded at 2 Mbps for a bits per pixel value of around 0.2. You can watch the video that Cube produced in the clip below; while a touch grainy in some sections, overall we've seen a lot worse quality.

Quality at 848x480 @ 500 Kbps. Yes, it was that big.

To try and improve quality, I lowered the resolution to 240p, which produced a stream at 360x240 resolution at the same 500 Kbps data rate. As you can see in the next clip, most of the graininess disappeared, but the much smaller resolution image understandably looked fuzzy when scaled to full screen. A 360p resolution would really have been helpful for the 600-800 Kbps data rate target.

Quality at 360x240 @ 500 Kbps

In terms of latency, or the delay between the actual event and the display of the video on screen, Cube was outstanding, in the 2-3 seconds range. For some news gathering operations, this should be fast enough for Q&A between the anchor and the remote reporter, so long as the reporter remembers to start nodding sagely when the anchors question is almost finished. I've seen latency in the 15-20 seconds range for some competitive products; for Cube this is a real strength.

To be clear, however, these were low-bandwidth tests over an Ethernet connection. I did not test latency under 4G broadcasts, which is likely to be at least slightly longer. With that as prologue, let's look at our 4G tests.

4G Tests with the Bond

Again, the Bond is the 4G modem aggregation tool that connects to the Cube via USB. It comes with 5 USB slots for 4G modems that can be from different service providers, providing a stream aggregation and diversification function.

To use the Bond, you need a Sputnik server installed. That's because, in operation, Bond packetizes the output from each modem and sends them separately to the Sputnik server for reassembly back into a stream that your streaming server can understand, and delivery to that server.

You have three options for installing the server: You can download and install it on your own Linux server, buy a Linux server box from Teradek that's pre-configured with Sputnik for around $1,000, or rent an EC2 cloud instance for between $20-$40/ month depending upon traffic. For my tests, I used an EC2 cloud instance that Teradek provided.

Speaking of my tests, given the lack of 4G service for my home, I loaded up the truck and headed 10 miles east to Interstate 77, where Verizon had a 4G hotspot. Teradek had provided four 4G modems; fortunately, two were from Verizon, one from T-Mobile and the fourth from AT&T. Status lights on the back panel let you know which modems are connecting and which aren't, though the iPad app provides even more information, as you can see in Figure 1 (below).

Figure 1. The iPad app let me know which modems were working.