Framerate is 24.000384 not 23.976 - is this a problem?

[nick1977]

Hi all

Not sure if this is the right forum to put this under, but will give it a go!

I've been ripping some of my BDs to put on my PC, and for the most part they all show up as 23.976 framerate.
This means I can access the mkv from my networked BD player (LG BD390) and they play back fine.
However yesterday I came across a disc that when ripped was showing as framerate 24.000384 in VLCplayer. I wasn't sure if it was the player with an issue, so I opened it with mediainfo and it said the same thing.
I tried adjusting the framerate in mkvmerge to 23.976 and sure enough it does add about 6 seconds to the running time, and the audio (understandably) goes out of sync. The BD was imported from Amazon Germany, and has an MPEG2 video stream, but does say 1080p on the back and is a genuine title not some dodgy copy. I don't think this has anything to do with it but may be wrong.

The main question I have is, does this slightly different framerate affect the playback at all? My BD player is set to output at 24p where appropriate, and my TV can receive it OK, but is one or both of them doing some fancy/messy conversion work? To my eye it looks fine, but my OCD side is curious if something is going on, as if there is it should be quite easy to convert the audio to run at the right speed!

Hopefully someone can help.

Thanks
Nick

[manono]

Since 24.000384fps isn't an acceptable Blu-Ray framerate, I don't think you should worry at all. It's most likely really 24fps which might explain why changing it to 23.976fps caused the audio to go out of synch.

I tried adjusting the framerate in mkvmerge to 23.976...

If it were I, I would have thought not changing anything at all would have kept it in synch. Have you tried that yet?

[nick1977]

Thanks manono

Yes, I have tried that and it plays back perfectly. My concern is whether the video being 24.000384 is an issue for playback.

When the frame rate is adjusted to 23.976, the audio goes progressively out of sync as the film goes on. I tried using mkvmerge to adjust the speed of the audio too, which it does, but only by putting a moment of silence in every 10 seconds or so! I know this would need to be recompressed to correct the speed effectively (it's DTS 5.1 channel)
Seems really odd that a bluray should have a non standard framerate. I think it must be the framerate that is wrong rather than just the flag, otherwise the audio would be out too.

Very confused!

Nick

[nick1977]

Just thought maybe I'm not being very clear with my question, so to summarise:

1) The ripped file plays back fine - no sync issues
2) It is reported as a framerate of 24.000384, which is non standard for Bluray - this is reported by both vlcplayer and mediainfo
3) If I change the video flag to 23.976, the audio goes out of sync progressively during playback, and the file is reported as 6 seconds longer.

So I suppose what I need to know is

a) Is it the ripped file most likely actually 23.976fps despite both programs showing it to be 24.000384?
b) If the file is actually 24.000384, is there any conversion work being done by either my bluray player or my TV when playing back? If so I will look to slow down the audio and remerge the mkv at the correct speed, as I want a proper 24p playback.

Thanks
Nick

[poisondeathray]

VLC is likely reading the frame rate slightly off.

24.0p AND 23.976p (24000/1001) are BOTH valid framerates for BD. Likely that BD is 24.0p

The only way to get "proper" 24p playback , is if you have a TV setup that can display 24.0p or some integer multiple (refresh rates are multiples of 24.0, such as 120Hz, 240Hz, etc...), then it's only repeating frames at regular intervals and no judder cadence (where you have some frames displayed longer than others). In North America most TV's run at 60Hz, so you get a 3:2 judder cadence (which I guess you could argue is "normal", but it's not "proper"). Not sure how the TV's are in the UK, but if they are at 50Hz, you won't get "perfect" playback either

[manono]

So I suppose what I need to know is

a) Is it the ripped file most likely actually 23.976fps despite both programs showing it to be 24.000384?

I already told you it's probably 24fps.

b) If the file is actually 24.000384...

It can't be so it isn't. Why are you repeating already answered questions?

...is there any conversion work being done by either my bluray player or my TV when playing back?

pdr covered that one. You probably aren't viewing 24fps playback anyway but 50fps with repeated frames.

[nick1977]

Thanks guys
Sorry I didn't mean to repeat questions. I didn't actually realise that 24p and 23.976 are different (I always assumed that 24p was just a simpler way of saying 23.976p).
My plasma TV does 4:4 pulldown of 24p apparently, so displays at 96hz.

I must confess to still being a bit confused by the some of this though. Is there a tolerance of some sort built into the TV with regard to the refresh rate? Otherwise either the 23.976 or the 24 fps would need some kind of interpolation to display correctly. Probably the 23.976, but that is the fps most blurays seem to be! Or does the bluray player automatically adjust the speed slightly, since it supports both rates (something I learned today!)

Thanks
Nick

[newpball]

TOtherwise either the 23.976 or the 24 fps would need some kind of interpolation to display correctly.

No, if the display refreshes exactly at 24p (or a multiple) it will simply change the 23.976 to 24.

That is, if the display is well engineered!

With a HTPC you can 'clock' things exactly, again assuming everything is well engineered.

Of course there is absolutely no reason for modern displays devices not to be able to display at non integer refresh frequencies but unfortunately that concept is usually one bridge too far for firmware engineers.

Also handshakes to change the refresh rates take usually longer than it takes light to go from here to the moon. There is no real technical hurdle to make that near instantly, just sloppy engineering standards.

[nick1977]

Thanks, although this does raise a thought, which hadn't occurred to me earlier.

I have the sound going from my BD player through to my surround system by coaxial.
So if it is the TV making the slight speed adjustment from 23.976fps to 24fps, why does the audio not go out of sync?
And how could the TV speed up the framerate as it won't be receiving the data in time if the player is only sending it at 23.976

I was thinking maybe the HDMI connection communicates both ways (handshake?), to ensure they stay in sync, or is there some other trickery involved for this to happen?!


Nick

[manono]

I didn't actually realise that 24p and 23.976 are different (I always assumed that 24p was just a simpler way of saying 23.976p).

You're right. For both NTSC DVD and for other formats (XviD, MP4, MKV, etc.) 24fps is often used when it's really 23.976fps that was encoded. For Blu-Ray it can be either:

https://www.videohelp.com/hd

So it helps to be more precise.

My plasma TV does 4:4 pulldown of 24p apparently, so displays at 96hz.

Really? Nice. No slightly jerky playback.