Netflix recently released its ISP Index for April 2018, with South Africa again posting a slight decrease in average streaming speeds compared to the month before.

There was not much overall movement in the chart, however, with only Cell C and Vox swapping second and third place, and South Africa remaining at 50 out of 59 countries.

Every ISP on the South African index showed a slight decrease in streaming speed, ranging between 0.38% to 4.9%.

While this explained the average decrease for South African ISPs overall, it raised the question: what caused the Netflix streaming speed of every ISP in the top 10 to decline?

In response to questions from MyBroadband, several Internet service providers said they could only speculate as to why the Netflix ISP Speed Index for South Africa declined.

Cybersmart’s Laurie Fialkov said they have seen huge uptake of lower-speed uncapped fibre packages, though, which might explain the 1.97% decrease in their average.

“If you see a further reduction in average speed across the board on the next index, then I believe it is a result of wider adoption across lower package speeds, which would lower the average for everyone,” said Fialkov.

Afrihost and Cool Ideas also stated that they could only speculate.

Paul Butschi from Cool Ideas said a possible factor may be that Netflix tweaked its codecs.

“It’s possible that Netflix has improved their video compression and it requires less bandwidth,” added Afrihost.

“There could also be lots more demand for their product from users viewing in lower resolution, and therefore at slower speeds,” it said.

NAPAfrica, where Netflix exchanges traffic with Internet service providers in South Africa, said it definitely wasn’t a capacity problem.

“Netflix has sufficient capacity to the exchange, and their peak during April is still below the threshold where we start worrying,” NAPAfrica told MyBroadband.

Not only South Africa

Netflix told MyBroadband that the phenomenon of seeing decreases across ISPs on the index is not limited to South Africa.

“This is seen in other markets and can be due to our recent launch of new encodings. Generally, the trend is up a bit, but there will be months when the encoding on certain content moves them all a step down,” said Netflix.

Netflix first published the details of its per-title encoding optimisation capabilities in 2015.

Per-title encoding allows Netflix to deliver higher-quality video under low-bandwidth conditions – including in titles with “simple” content, such as BoJack Horseman.

Per-title encoding will also often give users better video quality for complex titles, such as Marvel’s Daredevil.

Netflix also pointed out its ISP Speed Index for March 2016, in which two sequential months of average streaming speed decreases were seen in the United States.

“That movement as a group reflects more efficient streaming on those networks, due to our encoding work,” said Netflix.

“For example, with the new encodes, the first episode of House of Cards Season 4 streamed 720p starting at 910kbps, and 1080p starting at 1,620kbps on TVs.”

Previously, the lowest bit rates for the same streams were 2,350kbps and 4,300kbps, respectively.

Now read: The TVs Netflix recommends for 2018