How to TDecimate to 23.976fps with 30fps capture device

[tyee]

Just got an Epiphan av.io HD capture box. It can do up to 1080p60. Just for fun and to test it I put a Bluray into it and am capturing with vMix software, which is great btw. Problem is the capture box only seems to output 15, 30, and 60fps. I used alternate capture frame rates with vMix but got lots of frame drops when using anything other than 30 or 60. So I chose 30fps which is closer to the source, but since it's capturing at 30fps it's adding duplicate frames now and then. I did seem to count an extra duplicate every 5 frames but on another capture I counted 3 duplicates in a row! I tried TDecimate() with no specific options but it's not deleting all duplicates. Can you suggest the proper options for this capture? Is it actually possible to get back to 23.976fps?

[KarMa]

Assuming this source is progressive and actually needs to be 23.976, you can try TDecimate(mode=2, rate=23.976). It will look 100 frames ahead and do a better job of finding and removing duplicates. Your video may also be 25fps (PAL) in origin, so keep that in mind.

[LMotlow]

Just got an Epiphan av.io HD capture box. It can do up to 1080p60. Just for fun and to test it I put a Bluray into it and am capturing with vMix software, which is great btw. Problem is the capture box only seems to output 15, 30, and 60fps. I used alternate capture frame rates with vMix but got lots of frame drops when using anything other than 30 or 60. So I chose 30fps which is closer to the source, but since it's capturing at 30fps it's adding duplicate frames now and then. I did seem to count an extra duplicate every 5 frames but on another capture I counted 3 duplicates in a row! I tried TDecimate() with no specific options but it's not deleting all duplicates. Can you suggest the proper options for this capture? Is it actually possible to get back to 23.976fps?

Would suggest you take a look a look at the official specs for BluRay. Where did you get that BluRay, BTW? 1080p/60 isn't valid for commercial BluRay. https://www.videohelp.com/hd#tech

[KarMa]

Where did you get that BluRay, BTW? 1080p/60 isn't valid for commercial BluRay. https://www.videohelp.com/hd#tech

He said it can capture at 1080p/60, not that the Bluray is playing at 1080p/60.

[LMotlow]

The capture device isn't suitable for the source. Or you can just keep trying.

[tyee]

Yes, it's just a regular BR playing at 23.976fps. Looks like there is no way to get the capture back to 23.976 except by KarMa's suggestion. I tried it and it still has glitches here and there.

[KarMa]

You can also do TDecimate(mode=2, m2PA=true, rate=23.976) which will remove that 100 frame limit and go as far as it needs to go to find a cycle. It gives the same result as a 2 pass scan. But depending on the source, it can cause avisynth to become unresponsive for a couple of minutes when it starts. So if it locks up for awhile, it's normal.

Additional thoughts: I know someone with a Hauppauge Colossus who encodes shows off his cable box's component analog output, using his computer as a DVR. Anyway he had trouble with it not being able to encode every frame, causing it to duplicate the previous frame and dropping the actual frame that should have been captured. Upon play back, the missing frames were obvious. I don't know how he fixed it.

[manono]

Yes, it's just a regular BR playing at 23.976fps. Looks like there is no way to get the capture back to 23.976 except by KarMa's suggestion. I tried it and it still has glitches here and there.

You can try DeDup and/or MultiDecimate.

[LMotlow]

Why capture (re-encode) in the first place? Why not decrypt/rip BluRay to 1:1 copy. Or is this just an exercise? It would be interesting to see how it turns out.

[tyee]

Yes, it was just an exercise to see if it could be done. I just took a look at the Magewell XI100DUSB device specs which does basically the same as this Epiphan. Here are the Magewell capture rates -

Frame Rate: 25 / 29.97 / 30 / 50 / 59.94 / 60 fps

So...both devices do not support 23.976. I wonder why? Is it kind of obvious (an unspoken rule) or is it that no cameras output this frame rate so why support it?

@KarMa - I tried TDecimate(mode=2, m2PA=true, rate=23.976) and it works pretty good but still there are duplicates. I guess in my capture a cycle is not constant, there must be random duplicates so TDecimate would not work in that case would it? DeDup and Multidecimate are 2pass which may work.

[KarMa]

If your card supports 29.970, I would go with that over 30. Since 23.976 is perfectly 4/5 of 29.97. And for 24fps use a capture of 30fps, since it is also a perfect 4/5. Will probably give you a more reliable pattern.

[tyee]

Do you think this is a hardware limitation or firmware (not having those rates available)?

[jagabo]

The standard broadcast frame rates in the USA are 29.97 interlaced and 59.94 progressive. Reducing either of those to 23.976 progressive requires smart decimation. That's why capture devices don't capture 23.976 fps progressive.

[tyee]

So why doesn't Epiphan support 29.97 and 59.94? I shall give them a phone call tomorrow!

[jagabo]

So why doesn't Epiphan support 29.97 and 59.94? I shall give them a phone call tomorrow!

The terms 30 fps and 60 fps are often used as shorthand for 29.97 fps and 59.94 fps. Have you checked the captured files and verified the frame rates?

[tyee]

Yes, mediainfo says 30.000fps on my captures. Just tried all other capture choices again and I still get the same results, that is, drops when I select anything other than 30 or 60fps, then of course the duplicates appear. I have sent off an email to them also.

[jagabo]

Sounds like crappy software.

Most of the time when you capture 29.97, 30, 59.94 or 60 fps you will have duplicate frames. About the only time you won't is with live sports or news. Ie, anything that was shot on film (most movies and older TV shows) was shot at 24 fps and has to have duplicate frames when broadcast at TV frame rates.

[tyee]

Just an update, I called epiphan and got the latest beta firmware which I then tried on a 23.976 source and it started capturing ok, but then it started to drop frames also. Strange. If I paused the source then played again the capturing was good for a while then dropping occurred again. I will try it with a 29.97 source soon and see if that is ok.

[tyee]

Got a new firmware version again. Will test this week.

Update - Now it starts capturing just great at 23.976 but after a couple of minutes it drops frames but only in the display of my software (Vmix), Vmix stats show no frame drops! If let run like this, dropping frames, a few minutes later, it fixes itself and captures all frames just great. Strange.