Its one of those little things that drives me crazy.
I just can’t tolerate watching the News, a film or even Flog It! when the speakers lips don’t move accurately in time with the spoken word.
Its been a problem here at Bodgit Manor for a while. Steaming video to our LG TV has been hit & miss, where its sometimes OK, and at other times we lose sync and it seems to stay that way until we perform some kind of reset or change service.
Up until very
recently we still had the advantage of a TV aerial connection, where
lip-sync is not a problem. However, after moving all the furniture,
we now have the TV at the opposite end of our living space, so no
more TV aerial connection! All content must now be streamed.
We tried using our LG smart TV (which, incidentally, I’ve hated since the day it arrived!) like everyone else seems happy to do, but we miss ‘Live/linear’ TV and the convenience of the British service called ‘Freeview’; this groups all the digital channels together in one place, and provides a sensible Program Guide.
So the other day we invested in a Freely set-top box from Manhattan (...the company that is, not the district) to overcome our loss of Freeview.
Its great! Us old folk are back in our Happy Place where we can 'watch whats on telly tonight' and simply restart anything that's already started.
But we still had the lip-sync problem when video streaming, which I think may have been worse due to the slightly weaker wifi where the TV was now located.
Note: although you can normally delay the audio relative to the video via system settings, our problem was that the audio always lagged behind the video, and this delay period was frequently changing. Therefore no adjustment can rectify this.
Data rate (‘speeds’) for video
As a guide, for acceptable video streaming to a UK TV, the following data rates are generally required:-
- Standard Definition (SD): 3 - 5Mbps
- High Definition (HD): 5-10Mbps
- 4k video: 20 – 25Mbps
We still have a ‘copper’ service to the house, so our rated download speed, according to the router, is about 50Mbps. And using the BT Speed Tester from within our home network, this can typically ‘clock’ anywhere between 35 – 48Mbps.
Wifi Repeater
The chimney breast, as the main building feature between router and TV, was probably the primary reason for weak wifi signal. Nevertheless, it should have been high enough to provide an acceptable signal, and on ‘good days’ it was.
I added a plug-in wifi repeater to increase range, and checked that the incoming signal to the repeater was strong AND the repeater to TV signal was strong. Speed testing at this point (using laptop) gave about 40-43Mbps.
This initially appeared to solve the problem, based upon a couple of hours of TV viewing. However, it still wasn’t good longer term, and sometimes the video-audio delay was (subjectively) almost 1 second!
PowerLine ethernet adaptors
I found a pair of very old TP-Link PowerLine adaptors (PA411) in the loft, which are designed to the HomePlug AV standard. I connected one to the router via a lan port, and the other to my laptop via the ethernet port, but using a mains socket close by my TV.
As suspected, the speed was not great. The router was on a different mains circuit (‘ring main’) to the TV; speed was about 10 - 15Mbps and very variable. However, I connected the second PowerLine to my Manhattan box and used it for a couple of evenings ...then a couple more ...then a couple more.
The results were very good; these 10 year old TP-Link devices had properly fixed lip-sync!
What is going on?
Ping went the strings of my heart
I started Ping-ing to look for clues, and eventually set up a test using a Linux terminal on my laptop.
The command:-
ping -i 0.2 -c 9000 192.168.1.254 | tee ping_test.txt
...Pings the router 5 times per second for approx 30 minutes (9000/5 seconds), while printing the results in a text file.
Although this showed the average ping times were similar for wifi and PowerLine devices, the longest pings were over 1 second on wifi.
- Wifi average ping time: 8.2ms, max ping: 1118.5ms
- PowerLine: average ping time: 6.2ms, max ping: 14.9ms
So in effect, with my wifi setup, the video stream had a tendency to produce fast ‘bursts’ with some relatively long delays. And I think this is what upsets video synchronisation in the video device (TV or set-top box).
The lesson here is that the raw speed of your home wifi is a feeble way to judge the quality of the network; its like a child saying “this car is better than that car, because it goes faster!”
Home wifi is especially prone to problems which many would just call ‘noise’. More specifically, other activity on the same channel (frequency) posses a problem which may require a device to re-send data packets. But your router may also be busy transmitting data destined for other devices.
One worry I have about this explanation, is that the PowerLine transmission method comes with its own set of noise problems. And the large variation in data transfer speed seen in my BT speed test must surely classify this method as being ‘prone to noise’.
But a ‘driving a car’ analogy would be; “if you drive slower, brake gently & accelerate gradually, you give your passengers a smoother ride than you do if you drive as fast as you can, at every opportunity”.
PowerLine AV2 devices
More recent PowerLine adapters from TP-Link, like the TL-PA7017, are designed to the HomePlug AV2 Standard.
I thought it would be useful to get a pair of these for 2 reasons;
- I needed ‘mains power pass-through’ because I didn’t have enough mains sockets near either the router or the TV
- 4k video requires a higher data rate.
Rather surprisingly, just connecting one of these faster PowerLine device to the router, raised the ethernet speed for both the AV & AV2 devices on the network.
I now
get BT Speed Test results of about 42Mbps via both my AV & AV2
PowerLine devices, even between the 2 power ring-main circuits. However its not so great on the circuit which feeds our utility room and garage. But I suspect this is because its a noisy old radial circuit.
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