AV sync Audio delay slider precision

[alband]

Hi, Hope this hasn't been covered. I searched and found nothing.

I regularly use the VLC app to watch movies where the audio and video are slightly out of sync. The video is usually half a second before the audio, but it varies. If it's wrong by about 0.1 seconds, it's just about noticeable. If it's wrong by more than 0.2 seconds, it's quite distracting.

The slider to correct this can be found by tapping the "clock" icon, then adjusting the "Audio delay" slider. What a useful feature!

The issue is that this slider ranges from -30 to +30 seconds. It's only about 2 inches long! That's less than 1mm per second! Imagine trying to adjust down to 0.3-second accuracy. It's near impossible to be precise down to 0.2 seconds with that resolution. However, since the value is changed and shown in real-time in the top right corner, it's possible to get the right value eventually. So I can adjust until it reads"-0.56" (the value I most often need) then let go.
However, what makes the interface basically unusable, is that when I release my finger, the value jumps. I'll try it now, each time, setting it to "-0.56" then releasing. I get: "-1.01", "-1.12", "-1.01". It often seems to jump by about 0.5 seconds. I often spend minutes just trying to get the right value. And since I'm not actually aiming for a specific value - I'm aiming to get the audio and video to match up - I need the movie playing while I'm adjusting. So the result is that a minute or two is spoilt trying to get the audio right, and I have to skip back to watch it properly. You might think I've just got fat fingers or something. I insist I don't, but if you don't believe me, try it for yourself. Try setting it to any specific number. It's hard.

I would suggest decreasing the range of this slider so that more precise adjustment can be done. Say -5 to +5. I understand that a video might be +30 or -30 out of sync with its audio, but if I were watching a video that was, say, 20s out of sync, I would face the same problem outlined above getting perfect (non-distracting) synchronisation. Therefore, the ability to adjust to +/-30 is useless.
Hunting through the code this could be done by changing the values in "VLCMovieViewController~iphone.xib" line 257:

Code: Select all

<slider opaque="NO" contentMode="scaleToFill" contentHorizontalAlignment="center" contentVerticalAlignment="center" minValue="-5" maxValue="5" id="oQe-Uu-1HY" customClass="VLCResettingSlider">

I think the control could also be made wider by changing the next line which could allow a wider range to be used whilst still being precise.
I think there could also be some kind of bug, such that the value jumps when the user releases the screen. There is a small gap in time between the finger releasing and the value jumping, which suggests to me that another event it firing and doing something. No luck finding this though. It could just be an artefact of trying to get such precision from the slider.

Another option might be to use a different kind of control, for example, a roller, like the timer in the "Clock" app. One side of the roller would adjust seconds, the other side would adjust tenths of seconds. This would allow precise adjustment with a large range.

Otherwise a very useful app.

[Campdenhouse]

Having this same issue, which is aggravated by needing to use this feature to compensate for BT audio playback issues. It's a pain.

[alband]

I've played with it more and have other symptoms...

If I use the slider to pick a value (say -0.45), then hold my finger still, the UI eventually fades. Seconds after it fades, however, there is a noticeable change in the delay, and opening the panel again shows the actual value is different to what I set (e.g. -1.57).

Also, if I eventually set a good value, then skip to the next video, the *perceived* offset is affected. I think it accumulates per video. E.g. set it to -0.45, then go to the next video and the delay appears to be about -0.9. If I then set it to "0.0" the offset is correct. However, if I were to play the second video fresh, I would require an offset of about -0.45 again.

I too am using this to account for Bluetooth audio offset.

I think it basically comes down to this: It's impossible to adjust with sub-second accuracy. But it's easy to detect sub-second inaccuracies. Thus, the slider needs to be more precise, which given limited screen real-estate, means the slider endpoints must be lowered. Being able to adjust to -25 seconds is useless if you require -25.5 seconds.

[Lentife]

Came here to say this exactly. I love the feature and user or to cancel the auto delay of my Bluetooth headphones. -0.11 is perfect, but it's so hard to hit on both iPad and iPhone. Today I gave up after several attempts.
An easy fix in my opinion would be to set the slider range to -5 to +5 seconds or -2 and +2. Or to have an input field or setting toggle of a predetermined value. Might as well be a popular feature -> "fix BT delay" toggle.
Please fix this on the iOS app. Thanks so much!!

[PhredE]

Thanks to albrand for raising the subject of the rough audio delay slider. I too agree that it is particularly cumbersome and must having undergone little practical testing. It's now January 2019.

I notice that the 'time slider' on the top of the screen, while lacking the standard capability of allowing a tap on it anywhere along its length, lets a fingertip take the small current position marker disc and move it laterally - and, as the associated fade-in annunciator says, by also moving your finger vertically you can finely adjust the position of the current time marker. Lifting your finger from the screen does not induce any random jump.

I would hope that the same code could be implemented in the audio delay* adjuster so that fine and stable adjustments could be made with it.
You can move your finger off the audio delay adjuster line, but it doesn't allow any kind of fine control. It does let you get a better view of the millisecond count, but that's it.

(*I've spent a fair amount of time with this control but I do feel it is badly named: is a (positive) value used to correct an apparent audio delay or to create one? Its bland name doesn't help.)

[alband]

There's been an update and the slider is now resigned (at least on iOS). It's now in milliseconds instead of seconds and ranges from -5 to +5 seconds in 0.05s units. This is much better and basically solves the problem.
I think there is still a bit of "pop back" when releasing the slider, but I think this is likely iOS at fault rather than VLC. Also because the units are much smaller, it tends to only jump back by 0.05 seconds which isn't much. I'd say this bit of UI is fixed.

I have however noticed that if you apply a delay, then switch to another video or another app, the delay is sometimes maintained when viewing a subsequent video, even if the slider is back to 0. For example, open video A and apply 0.5s delay. Open video B, the slider will be back to 0. Apply a 0.5s delay again. The resulting delay will be 1 second.
I'm not 100% sure of this behaviour and can't test it right now but I've noticed it on several occasions. Either way, it's easy to fix with the more precise slider.
Regarding renaming the slider to know which way the audio/video is moving, maybe use the same label as in the desktop app that says "hasten audio" / "delay audio" as appropriate.

[PhredE]

Thanks for mentioning this, alband. I have noticed recently that on iOS (iPad-mini 4) the delay adjuster is better behaved. Less jumping around.
Although unlikely to be connected, other queer things have emerged, like double up-swipe doesn't invoke a jump back, and autoplay-next doesn't seem switchable. Somehow a mute tap has crept in. Others. Let's hope that the code is being cared for properly.

As for the naming of the sound slider, controls like this generally, yes, take the verb form, so 'Delay audio', agreed, but 'Catch up audio', perhaps. 'Bring forward'? ('Hasten' could imply speed up.)