Roku Device Features, Settings & Updates

[Shasarak]

My Streaming Stick+, when changing output refresh rate to match source frame rate, always switches to exactly 24Hz rather than the correct 23.976Hz, meaning that roughly once every 41 seconds you get a duplicated frame.

Is there a setting somewhere that makes it produce 23.976Hz output?

[Shasarak]

(bump).
Anyone...?

[Miami_Son]

You are confusing frame rate with frequency. They are not the same.

[atc98092]

But no, there's no setting to control the actual refresh rate. As Miami said, that's not framerate.

[Shasarak]

"Miami Son" wrote:
You are confusing frame rate with frequency. They are not the same.

I am most definitely not confusing frame rate with frequency (though it is, of course, a tremendous honour to be patronised by you ).

The point of the "Auto-adjust display refresh rate" setting is that, when enabled, the refresh rate should exactly match the video frame rate.

But it doesn't. If the video frame-rate is 23.976Hz, the refresh-rate gets set to 24.000Hz instead - which, as I said, causes the device to repeat a frame roughly once every 41 seconds, and produces a regular, slight stutter.

So I'm asking, is there any way to get refresh-rate to match the frame-rate precisely if the frame-rate is 23.976Hz?

[Shasarak]

Or, given that this is clearly a bug, is there any chance of it ever being fixed?

[Miami_Son]

Refresh rate and frame rate are not the same and are not tied to one another. The refresh rate in the US is 60hz, whereas in the UK it is 50hz. Using the wrong one will result in a distorted or flickering picture.

[ean611]

Roku Ultra 2018 does this.

This is a massive issue to me, it's clearly using the wrong frame rate. Looks like a systemic issue, as it's on multiple devices.

The correct frame rate for the majority of content is 23.976Hz, not 24.00Hz. As stated upthread, this will cause frame skips periodically. As this is one of only players for VRV supporting switchable refresh rate, would be lovely if this bug was fixed, not ignored.

[ean611]

"Miami Son" wrote:
Refresh rate and frame rate are not the same and are not tied to one another. The refresh rate in the US is 60hz, whereas in the UK it is 50hz. Using the wrong one will result in a distorted or flickering picture.

Just want to respond to this, Because yes, Refresh rate and frame rate are linked, as you generally want them to be the same thing.

For instance, if you use 59.94Hz for 23.976Hz content, as is typical for displaying movies on NTSC complaint displays, you get juddering. This is due to frame time. Each frame at 59.94 is 16.7ms, however, this does not have an even multiple from 23.976, where each frame is 41.67ms. Due to this, you end up displaying one frame for 33.4ms and the next frame for 50.1ms. 
To avoid these effects, you want to match your refresh rate with the frame rate of the source. Or use an even multiple, such as using 50Hz refresh rate for 25Hz content (see old BBC shows for 25Hz). The goal is to get each frame the same amount of time. Likewise with the error here, we have a frame skip every 41.67 seconds, as it takes that long for the alignment to no longer work for 23.976Hz and 24Hz. (Beat frequency of 0.024Hz).

There is sadly confusion on this topic, often with "higher is better" used. Unless that higher is 120Hz or 144Hz (over displayport or HDMI), higher is not better. We need an even multiple. 30*2=60, 23.976*5=119.88, etc. (Also, higher frame rate means that error due to beat frequency is much harder to see, with one frame going +8.3ms, but this requires an even multiple to start.)

[mike_s]

Thing is, it's a streaming stick. The upstream source isn't forcing or starving data, some gets buffered and then the stick just throttle it to the rate it needs to keep the buffer full.

So, where does this mismatch which supposedly causes a dupe or skipped frame happen? The stick is just feeding the display a frame at a time, at the rate it's doing. I'm sure it's not keeping two clocks and comparing them, then dupe or skipping to keep them in sync. 

I'll admit not looking into it deeply, but I strongly suspect the display does basically the same thing, and just accepts the frames and deals with it, whether 23.976 or 24 Hz. The HDMI clock is driven by the source, and I doubt any consumer display keeps an independent clock which needs to stay in sync. The difference in speed is insignificant to the viewer.

Edit: the one place it would matter is if trying to combine multiple video sources. But if you're doing that, you need to keep all the devices in sync anyway (simple crystal controlled timing is insufficient), and you'd be using a professional format, like HD-SDI.

24 Hz content vs 30/60 Hz frame rate is different. Actually showing 24 at 30 would result in a very user noticeable speed up of the content, hence the need for 3:2 pulldown.