Confused over frame rates being changed

[mattias83]

I'm about to start ripping some DVD features and extras to mkv and I want to make sure I do it correctly with the right tools.

I figured the easiest, safest way would be to use makemkv. But there's some confusing framerate discrepancies I'm encountering that's leaving me unsure if I'm using the best tool for the job.

For an example, disc 1 of Star Trek - The Animated Series (DVD). When ripping episode 1 in makemkv, the file reports the following framerate in mediainfo (relevant info):

Frame rate mode : Variable
Frame rate : 23.976 (23976/1000) FPS
Original frame rate : 23.976 (24000/1001) FPS
Scan type : Progressive
Scan order : 2:3 Pulldown

Both framerates are listed as 23.976 but note the difference in the parenthesis. Why did makemkv change the framerate here?

Ripping the same episode in mkvtoolnix (adding the vob file directly in mkvtoolnix as a source) at default settings reports this in mediainfo:

Frame rate mode : Variable
Frame rate : 23.976 (23976/1000) FPS
Original frame rate : 29.970 (30000/1001) FPS
Scan type : Progressive

Note the original framerate is being reported as 29.970 in the file created by mkvtoolnix.

Scanning the actual vob direct from the DVD in mediainfo reads:

Frame rate : 23.976 (24000/1001) FPS
Scan type : Progressive
Scan order : 2:3 Pulldown

Note the vob reports the identical framerate as makemkv's file reports the "Original frame rate".
Also note that both the original vob and the mkv by makemkv report Progressive with 2:3 pulldown; the file from mkvtoolnix does not list 2:3 pulldown.

So what's going on here? I've tried researching this and there's lots of confusion about varying framerates out there pertaining to DVDs.

- Why does makemkv change the framerate from 23.976 (24000/1001) as reported direct from the vob to 23.976 (23976/1000)?

- Why does mkvtoolnix report the original framerate as 29.970 (30000/1001)? It's an NTSC DVD so I'd expect 29.970 but the whole 3:2 pulldown thing confuses me a bit, especially since it doesn't seem to be handled consistently. Some DVDs appear to be encoded as 23.976 and some as 29.970. But why the discrepancies between these programs, and why is makemkv changing the reported framerates?

Both mkvs and the vob report as playing at 29.970 in vlc under tools>codec information.

Which software is ripping it correctly? Or is neither right? What should a correct mkv report for framerates based on the original vob info I posted?

[mattias83]

I've run into other DVDs that report this in mkvs created by makemkv:

Frame rate mode : Variable
Frame rate : 23.976 (23976/1000) FPS
Original frame rate : 29.970 (30000/1001) FPS

I haven't seen any yet that report the frame rate as 23.976 (24000/1001), even when that's listed as the "original frame rate" by makemkv and the vob itself. It either changes it to 23.976 (23976/1000), or sometimes it outputs the file as 29.970 (30000/1001), matching what the vob reports.

Does any of htis have to do with how mediainfo reads and reports the files? There must be something different about the files though (makemkv vs mkvtoolnix) as mediainfo reports different data between the two files (and the original vob). Is makemkv and mkvtoolnix modifying actual framerate data? I noticed if I try to force a framerate in mkvtoolnix (default duration / fps) it results in the file going wildly out of sync very quickly. So that's not the right thing to do.

How can I be sure I'm ripping these DVDs correctly? The difference between 23976/1000 and 30000/1001 is slight, but I still don't want to introduce any problems into the file.

[tomty89]

Why does makemkv change the framerate from 23.976 (24000/1001) as reported direct from the vob to 23.976 (23976/1000)

VOB (or more precisely the MPEG-2 video stream) does not report / store frame rate in fraction when the rate is a "standardized" rate (and 24000/1001 is such a rate). Instead it uses a code to indicate the rate (for 24000/1001 the code is 1).

Why does mkvtoolnix report the original framerate as 29.970 (30000/1001)? It's an NTSC DVD so I'd expect 29.970 but the whole 3:2 pulldown thing confuses me a bit, especially since it doesn't seem to be handled consistently. Some DVDs appear to be encoded as 23.976 and some as 29.970. But why the discrepancies between these programs, and why is makemkv changing the reported framerates?

AFAIK for properly encoded DVDs / MPEG-2 video stream, "NTSC 24p" pulled down to "NTSC 30p" would have the aforementioned frame rate code (which resides in "sequence headers" of the stream btw) set to the value for the latter (i.e. 30000/1001), which is 4. This is because each "picture" / frame in the stream comes with explicit "instructions" for the soft pulldown / telecine (namely "repeat_first_field" and friends in the "picture coding extension" (of the picture header). In other words, unless a decoder explicitly treat it as a "NTSC 24p" stream (by somewhat "ignoring" the "instruction"), the stream will be decoded into "NTSC 30p" output.

What makes thing even more complicated is that, some older DVDs / MPEG-2 video is not very "cleanly" pulled down, as in it is mostly pulled-down materials but mixed with interlaced "sequences". You could get into weird AV sync problem if you try to "IVTC" such stream (as the frame rate would literally "vary" during the course of playback then; and I'm not sure if most players can handle that very well). Also I don't know if there's actually tool for you to IVTC such stream. I've written some ugly C program (that works) because I had one cleanly pulled down DVD I would like to pull up for 23.976p playback. (There have been attempts to add such functionality to the MPEG2 metadata bitstream filter in ffmpeg, but for reasons / no reason they never made it to the upstream tree.)

P.S. I don't think the info you see in MediaInfo or so would matter a lot anyway. Regardless whether MakeMKV is doing the "correct" thing, AFAIK any "potentially wrong" metadata (from MakeMKV) resides only in the MKV muxing, which most players won't even care anyway.

---

Scan order : 2:3 Pulldown

Btw I don't know much about Matroska / MKV, but as per the the output you have given, apparently it has a field where a muxer can "mention" that the video is pulled down. I suppose you can see it this way:

Code: Select all

Original frame rate : 23.976 (24000/1001) FPS + Scan order : 2:3 Pulldown = Original frame rate : 29.970 (30000/1001) FPS

And most likely MakeMKV chooses the left side of = while mkvtoolnix choose the right side of it when setting the metadata.

Frame rate : 23.976 (23976/1000) FPS

I kinda doubt that this piece of information comes from any metadata in the muxing or MPEG-2 video stream. It could be based on multiple pieces of metadata obtained through probing the video stream (e.g. frame rate code being 4 + progressive frames found + ...). However I don't know MediaInfo very well. Have basically zero experience of using it too. I did contributed to mkvtoolnix for a bit in the past though, and I don't think it will set any metadata field to 23.976 fps (or equivalent) (or the "scan order" field if that exists):

(these are the lines relevant when you remux VOBs)
https://codeberg.org/mbunkus/mkvtoolnix ... r.cpp#L152
https://codeberg.org/mbunkus/mkvtoolnix ... s.cpp#L680
https://codeberg.org/mbunkus/mkvtoolnix ... .cpp#L1239
https://codeberg.org/mbunkus/mkvtoolnix ... _2.cpp#L29

(these are the lines relevant when your remux an MKV that has no default duration set)
https://codeberg.org/mbunkus/mkvtoolnix ... 2.cpp#L127
https://codeberg.org/mbunkus/mkvtoolnix ... 2.cpp#L254
https://codeberg.org/mbunkus/mkvtoolnix ... 2.cpp#L185

As you can see, the only case it will do so is when your MPEG-2 video stream has the "NTSC 24p" frame rate code, which as I mentioned is not something that should happen in a "proper" DVD (AFAIK). (I don't think 24p or "NTSC 24p" DVD without soft pulldown is ever a thing / allowed btw, even though MPEG-2 itself allows it.)

P.S. I'm not really sure if it is correct to called the pulled down material "NTSC 30p" btw. Perhaps "NTSC 60i" is somewhat more correct. Perhaps it's not. Just don't take it too seriously. You get the sense.

---

I noticed if I try to force a framerate in mkvtoolnix (default duration / fps) it results in the file going wildly out of sync very quickly.

Just noticed this line in your post. That is somewhat surprising. What's the default duration / fps comes with the MakeMKV rip / mux? And what value did you try to force?

[tomty89]

So I just checked MediaInfo 26.01 output for MKVs produced by mkvtoolnix 97.0 and makemkv 1.18.3 from the "cleanly" pulled-down DVD I mentioned, I cannot produce the difference you saw. Both of them give:

...
Frame rate mode : Variable
Frame rate : 23.976 FPS
...
Scan type : Progressive
Scan order : 2:3 Pulldown
...

And I think found out why the "Frame rate" is 23.976 FPS instead of 29.970 FPS in spite of the frame rate code being 4 (i.e. frame rate is 30000 / 1001), and where this "Scan order" comes from: https://github.com/MediaArea/MediaInfoL ... .cpp#L1347

When I checked the DVD directory with MediaInfo, this is what I get:

...
General
Complete name : KIBA-2320/VIDEO_TS/VTS_01_1.VOB
CompleteName_Last : KIBA-2320/VIDEO_TS/VTS_01_6.VOB
...
Frame rate : 23.976 FPS

Video
...
Frame rate : 23.976 (24000/1001) FPS
...
Scan type : Progressive
Scan order : 2:3 Pulldown
...

I have no idea why "Frame rate" of "Video" has (24000/1001) additionally or where it comes from yet.

VTS_01_{1..6}.VOB were the files passed to mkvmerge when I produce the MKV with mkvtoolnix (i.e. VIDEO_TS.VOB and VTS_01_0.VOB were left out).

[mattias83]

Thanks for digging into this for me. Lots of useful information, though I admit the various frame rates being reported with DVDs and even 29.970 material from blu-rays has definitely got me confused over what's the "correct" way to do it to not confuse external media players like Ziddo/Dune or PC media players like VLC or MPC-BE.

Forcing a frame rate in mkvtoolnix results in problem / out-of-sync files. It seems to create an mkv where the video is forced to the specified frame rate but the audio doesn't match since it's just a remux.

To complicate things, DVDs seem to vary widely. I'm seeing some VOBs report 23.976, and some 29.970, and some TV sets are a mix - one episode is 23.976 and another episode is 29.970 (Logan's Run TV series as an example).

Here's an example:

THE BRADY BUNCH (PILOT):
----------------------------------

With this disc, the vob reports 29.970 in mediainfo - note there's no mention of pulldown. Both makemkv and mkvtoolnix changes it to variable 23.976 (23976/1000) with no mention of pulldown, and both mkvs play fine. If I force 29.970 (30000/1001) in mkvtoolnix, it results in sped-up video and it's out of sync. So here, makemkv and mkvtoolnix are in agreement, for a 29.970 vob with no pulldown.

VOB:
Frame rate : 29.970 (30000/1001) FPS


makemkv:
Frame rate mode : Variable
Frame rate : 23.976 (23976/1000) FPS
Original frame rate : 29.970 (30000/1001) FPS


mkvtoolnix:
Frame rate mode : Variable
Frame rate : 23.976 (23976/1000) FPS
Original frame rate : 29.970 (30000/1001) FPS


mkvtoolnix forced 29.970 (30000/1001):
Frame rate mode : Constant
Frame rate : 29.970 (30000/1001) FPS

* Video is sped-up and audio is out-of-sync and gets further and further out of sync - video ends at 19:49 even though audio continues until 24.45 (full length of video)


Something else to note - every single NTSC dvd remux makemkv puts out plays at 29.970030 in VLC, which I understand is correct. Every one by mkvtoolnix plays at 29.970628, which is just a fraction different, but apparently not quite the standard speed NTSC should play at, which from what I could find out online is 29.970030.

Mkvtoolnix also doesn't rip chapters directly from VOBs, whereas makemkv does retain chapters. So I'd like to think makemkv is doing things right here. But I'm surprised how the two programs handle the same material.

[mattias83]

Another TV set example:

QUARK (PILOT)

This one gets more complicated. The VOB reports 23.976 (24000/1001) with pulldown. For some reason, makemkv changes it to variable 24.000 FPS and carries over the pulldown flag, and lists the original frame rate as 23.976 (24000/1001). Mkvtoolnix also changes it to variable 24.000, but lists the original frame rate as 29.970 (30000/1001) FPS and doesn't carry over the pulldown flag. Both files play fine in VLC, though there's the slight discrepancy I mentioned above where makemkv files play at 29.970030 and mkvtoolnix files play at 29.970628. Forcing the framerate in mkvtoolnix to either 24000/1001 or 30000/1001 results in speed and sync problems, so that's no good.

VOB:
Frame rate : 23.976 (24000/1001) FPS
Scan type : Progressive
Scan order : 2:3 Pulldown

Makemkv:
Frame rate mode : Variable
Frame rate : 24.000 FPS
Original frame rate : 23.976 (24000/1001) FPS
Scan type : Progressive
Scan order : 2:3 Pulldown

mkvtoolnix:
Frame rate mode : Variable
Frame rate : 24.000 FPS
Original frame rate : 29.970 (30000/1001) FPS
Scan type : Progressive

mkvtoolnix forced 23.976 (24000/1001):
Frame rate mode : Constant
Frame rate : 23.976 (24000/1001) FPS
Original frame rate : 29.970 (30000/1001) FPS
Scan type : Progressive

* Audio is out-of-sync and gets further and further out of sync

mkvtoolnix forced 29.970 (30000/1001):
Frame rate mode : Constant
Frame rate : 29.970 (30000/1001) FPS
Scan type : Progressive

* Video is sped-up and audio is out-of-sync and gets further and further out of sync - video ends at 20:35 even though audio continues until 25.43 (full length of video)


* So why are both programs changing the frame rate to an exact 24.000 for this episode? Not 23.976 (24000/1001) - an exact 24.000. Why not 23.976 (24000/1001) like other discs?

I'm unsure if I should just let makemkv do it's thing and trust it with all my TV sets. It just seems so inconsistent from one disc to another. Sometimes the output is 29.970, sometimes 23.976, sometimes 24.000, sometimes it's changed, sometimes it's not.

[tomty89]

With this disc, the vob reports 29.970 in mediainfo - note there's no mention of pulldown. Both makemkv and mkvtoolnix changes it to variable 23.976 (23976/1000) with no mention of pulldown

Well this is what I get for another DVD (which is essentially a "previous generation" of the "cleanly" pulled-down disc I tested):

Code: Select all

...
General
Complete name                            : KIBA-1004/VIDEO_TS/VTS_01_1.VOB
CompleteName_Last                        : KIBA-1004/VIDEO_TS/VTS_01_6.VOB
...
Frame rate                               : 29.970 FPS

Video
...
Frame rate                               : 29.970 (30000/1001) FPS
...

Code: Select all

Frame rate mode                          : Variable
Frame rate                               : 24.000 FPS
Original frame rate                      : 29.970 (30000/1001) FPS

(identical for both makemkv and mkvtoolnix mux)

Also no mention of pulldown, even though I know most of the "sequences" are "NTSC 24p" with soft pulldown applied. (There are short portions in between the pulled down materials that are "NTSC 60i / 30p". Perhaps there is such a portion at the beginning too. I don't really remember.)

The thing is mediainfo itself is quite "complicated" too. There's basically no way in telling what exactly it reports are referring to, at least not without knowing all the "heuristics" in its code and maybe also the details of the video stream / file -- in which case the purpose of it would be "defeated". That's a big reason why I never bothered to "check" any file with it.

---

To be honest, I have no idea what exactly do you mean by "forcing 29.970 (30000/1001) in mkvtoolnix". (Obviously it's not setting default duration for the video track? AFAICT it should have already been set anyway.) But I do think I know the consequence of that: basically the soft pulldown would be "disabled" but the frame rate is still 30000 / 1001 fps.

When the soft pulldown is "enabled" (i.e. applied as "instructed"), essentially half of the frames would last for (1001 / 30000 * 1) second, and the half of them would last for (1001 / 30000 * 1.5) second. In other words, with the pulldown applied this is what happens for 24000 / 1001 frames:

Code: Select all

(12000 / 1001) * (1001 / 30000) + (12000 / 1001) * (1001 / 30000 * 1.5)

which last for 1 second in total.

And by "forcing 29.970 (30000/1001) in mkvtoolnix", this is what happens for 24001 / 1001 frames:

Code: Select all

(24000 / 1001) * (1001 / 30000)

which last for 0.8 second in total. (19:48 / 24:45 is also 0.8.)

---

Mkvtoolnix also doesn't rip chapters directly from VOBs, whereas makemkv does retain chapters

mkvmerge allows you to retain the DVD chapters through --chapters path/to/video_ts_directory:title_number. (Not very familiar with the mkvtoolnix GUI, but probably there's somewhere you can instruct it to do the same thing.) Rather what mkvtoolnix doesn't support is retaining DVD subtitles (although it supports retaining DVD subtitles in MKV and importing from "VobSub" files; just not directly from the DVD backup).

[tomty89]

I'm unsure if I should just let makemkv do it's thing and trust it with all my TV sets.

Well the bottom line is, you can always check whether the MPEG-2 stream is "intact", as in, you can crosscheck the hash of the video stream extracted from the VOBs / MKVs:

Code: Select all

ffmpeg -i "concat:1.vob|2.vob|..." -f mpeg2video -c:v copy | sha256sum
ffmpeg -i makemkv.mkv -f mpeg2video -c:v copy - | sha256sum
ffmpeg -i mkvtoolnix.mkv -f mpeg2video -c:v copy - | sha256sum

mkvextract with --raw should also give you the intact MPEG-2 video stream. (Unless there is something wrong in the muxing / in mkvtoolnix, you should get the exact same stream without --raw. In other words, if you get output files that are different, probably there's something wrong, or perhaps just "imperfect", in either the muxing or mkvtoolnix.)

[mattias83]

I'm sure the video is being remuxed intact. What I'm concerned with is the ripping programs altering the flags and headers, affecting how the file is played back with my software or external media players.

When I say forcing a framerate in mkvtoolnix, once a vob (or any file) is loaded into mkvtoolnixGUI, I can click to highlight the main video stream in the left window, and then in the right side properties box, under "Timestamps and Default Duration", there's a box titled "Default duration / FPS". You can input your fps in that field, which affects the output. For 29.970 or 23.976, I've been using this format:

30000/1001 for 29.970, or 24000/1001 for 23.976.

But as I mentioned this just throws the sync off, and the video speeds up in playback. I'm not sure what mkvtoolnix does when you fill in that "Default duration / FPS" box but it must be altering timestamps or something, which is throwing the sync off.

I loaded the Quark mkv, which I forced to 29.970 in mkvtoolnix, into VirtualDub, and the video and audio have different durations:

Video: DURATION = 00:20:35.367000000
Audio: DURATION = 00:25:43.168000000

So that explains why the sync is drastically off and the video plays sped up.

I was thinking that would be the way to make sure the remuxed mkvs keep the original frame rate, which is what this thread was created for, but that's definitely not the answer.

The reason I started worrying and messing with the frame rates in the first place is when I was noticing the mkv frame rates often differ from what the "original frame rate" scans at or plays back at. Playing mkvs from Makemkv plays back at 29.970 in VLC, despite mediainfo reporting 23.976. Playback seems correct, but I want to make sure it's playing correctly without any sync or timing issues.

And as mentioned sometimes makemkv outputs 29.970 from VOBs, sometimes 23.976, and sometimes 24.000. Usually it's 23.976, which is why I'm confused when it sometimes outputs as 24.000 instead. Is that anything to worry about?

Or is that going back to mediainfo possibly playing a factor in how it's reading the files?

In the end, I just want to make sure I'm ripping these DVDs to mkv correctly, so that the timestamps aren't messed up and throw off my media players, especially Dune or Zidoo. VLC seems to be handling these mkvs fine from Makemkv; regardless if it says 23.976, 24.000, or 29.970, VLC seems to play them back at 29.970 according to VLC. But I'm not sure how Dune or Zidoo will play these files depending on which framerate it reports.

I thought the goal was always to make sure the original frame rate matches the output frame rate in these remuxes, but that doesn't seem to be the case?

I'm still confused why all the DVD TV series MKVs from Makemkv play at 29.970030 in VLC, but the ones from mkvtoolnix play at 29.970628. From what I could find looking it up, 29.970030 should be what is expected. But apparently some programs do rounding or truncate decimals.

A Reddit post 4 years ago also mentions this issue with mkvtoolnix:

"When remuxing Blu-rays with MKVToolNix GUI v60.0.0 using default settings, I have found that it changes the frame rate as reported by VLC. Specifically, it takes 23.976000 fps and the Blu-ray standard of 23.976024 fps (24000/1001) and changes them to 23.976216 fps. Same for NTSC video; it changes from 29.970030 fps to 29.970628 fps."

According to another forum, technically that means if the video is long enough, there could be a slight drift in sync:

"DVDs and BDs have to be exactly 30000/1001 fps. But the authoring program may simply take a "close enough" rate and rewrite the header with the exact one.

The drift will be equivalent to 1 frame every 1/(file_fps - 30000/1001) seconds.

1/(29.970628 - 30000/1001) = ~1672 sec = 27 min 52 sec"

So with mkvtoolnix there could be a slight drift in sync by 28 minutes when playing MKVs ripped from VOBs, if I'm understanding correctly. Which is what I'm trying to avoid - any unnecessary frame rate or sync issues in my remuxes.

[tomty89]

there's a box titled "Default duration / FPS". You can input your fps in that field

Hmm, to be frank I don't really know what filling that in would do. As I mentioned, default duration of the video track should be set "out of the box" for DVD remux produced by mkvtoolnix. I also checked output from MakeMKV with mkvinfo, and the field seems to be set as well. (FWIW, remux of NTSC DVD it should always get the value of 30000 / 1001, because that's the only value allowed in the sequence headers, even in the case of DVD with "NTSC 24p" material and pulldown. The only other allowed frame rate code would be the one for 25p -- allowed only for PAL DVDs, obviously)

My guess is that when you use the GUI (and maybe also the CLI, idk) to set it manually, mkvtoolnix would remove all the frame durations (which as I mentioned, for half of the pulled down frames would be the same as the default duration, and for the other half it would be 1.5 times of that). When that happens, all the frames would last for the default duration, hence the total length shrinking into 80% of the original (1 / (0.5 + 0.5 * 1.5)).

I was thinking that would be the way to make sure the remuxed mkvs keep the original frame rate, which is what this thread was created for, but that's definitely not the answer.

So probably no, because you need the varying / "switching" frame durations to keep the original frame rate, let alone that it's unclear what "frame rate" and "original frame rate" respectively mean in MediaInfo anyway.

Playing mkvs from Makemkv plays back at 29.970 in VLC

That's totally normal. That's exactly the point of pulldown -- to keep the frame rate fixed at that even when some / all of the materials were originally "(NTSC) 24p", through the means of making half of the frames last longer during playback (12 + 12 * 1.5 = 30).

And as mentioned sometimes makemkv outputs 29.970 from VOBs, sometimes 23.976, and sometimes 24.000. Usually it's 23.976, which is why I'm confused when it sometimes outputs as 24.000 instead. Is that anything to worry about?

I don't think you should be, especially when you are not experiencing any actual / "visual" problem during playback. As far as I can see it's really just a value "calculated" by MediaInfo based on different factors.

AFAICT the only case you would need concern is when you literally want 24p / 23.976p playback, i.e. you want to apply ("soft") IVTC / pullup and make it "fit" with e.g. screen refreshing at 24Hz / 23.976Hz. But then what you would need to concern is not (just) the muxing, but whether the video stream is "clean" (as in, purely pulled-down material).

A Reddit post 4 years ago also mentions this issue with mkvtoolnix

First thing first: what version of mkvtoolnix are you using?

I can't rule out that maybe for reasons the frame durations generated by it is not accurate enough (due to precision / rounding problem or so), but there would be little meaning (IMHO) to discuss about it if you are using archaic version.

When remuxing Blu-rays

Also Blu-ray would be a whole different story. I mean like it is handled by totally different code in the program because of different container and likely different codec (AVC for most of the time).

[mattias83]

I'm using MKVToolNix GUI v98.0 "Chonks" 64-bit on Windows 10.

"(FWIW, remux of NTSC DVD it should always get the value of 30000 / 1001, because that's the only value allowed in the sequence headers, even in the case of DVD with "NTSC 24p" material and pulldown. The only other allowed frame rate code would be the one for 25p -- allowed only for PAL DVDs, obviously)."

That's why I've been confused. I expected to see 29.970 (30000/1001) in mediainfo when I drop these DVD remuxes in. So when I started seeing 23.976 and 24.000, I started worrying. I know lots of video-shot NTSC shows are 29.970 straight to tape, but the shows I've been remuxing were all shot on 35mm film, then transferred to NTSC DVD. Though again, sources seem questionable sometimes - I don't know why one episode of Logan's Run remuxes to 29.970 and another to 23.976. Maybe inconsistent authoring or sources used for the DVDs?