Testing is done and here are my findings.
I tested with the following routers:
- Asus RT-AC68U
- Asus RT-AC88U
WiFi networks from neighbors were limited to 4 on 2Ghz and 0 on 5Ghz.
The test file used was La La Land
File size : 54.5 GiB
Duration : 2h 7mn
Overall bit rate : 61.0 Mbps
Server mounted through SMB in fstab.
Test 1
Vero 4K connected via RJ45 cable through the on-board ethernet interface.
As expected the iperf3 test showed avg. 93.1Mbit/s
Playing the film the incoming data stream could barely saturate the buffer to 100%. But it managed okay, with only a few skipped frames through out the movies. 1 drop 29 skipped in the first 10 minutes.
Test 2
Vero 4K connected to AC68U via 5GHz through the internal wifi antenna.
iperf3 test showed avg. 235Mbit/s
Playback was barely possible. Buffering every 20-30 seconds. Looking at the bitrate of the video and audio stream, it looks like the actual throughput was 40-50Mbit/s. Because as soon as the film jumped to 50+Mbit/s the buffer would fall. Pausing at letting the buffer fill up only postponed the same outcome.
Test 3
Vero 4K connected to AC68U via 5GHz through the internal wifi antenna.
Changed the TxPower to 178mW, 150mW, 130mW, 100mW
No changes to the playback. Same results as Test 2 showed, except 100mW here the iperf3 test started to show that the throughput was lower.
Test 4.0
Vero 4K connected to AC88U via 5GHz through the internal wifi antenna.
TxPower at 100% (no idea how much in mW as the firmware only shows procent)
iperf3 showed avg. 73Mbit/s
I tested the film anyway, but playback took couple of minutes to begin. Did not even feel like doing measurements since it was very clear that the buffer barely could fill up…
Test4.1
Changed the TxPower to 50%
iperf3 showed avg. 231Mbit/s
Playback displayed exact same behaviour as test 2
Extra info
In all tests the alignment of the Vero4K box was flipped on 3 different angles but showed no difference in iperf3 or playback. Vero4K was placed the recommend distance from the router at 2.5 meters.
Conclusion
The problem lies not with the server, so that leaves the router and the antenna of the Vero4K
The odds of the routers being the problem seems very low. I could try doing the same tests on my phone and tablet, but the fault seems to lie not with the wifi connectivity but with the way Kodi ingest the bitstreams.