Jittery Video?

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ashlar Offline
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Post: #331
ArtVandelae Wrote:Now, if you are resampling by a large amount in the case of converting a 25fps PAL video to 24fps, which is a full 4% change, then, yes, there will be an audible difference.
And thank god for that! You'd be then listening to the original pitch in 99% of the cases where movies are concerned.
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dpassent Offline
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Post: #332
ashlar Wrote:And thank god for that! You'd be then listening to the original pitch in 99% of the cases where movies are concerned.

which brings another idea. would it be cool that user can choose what fps switch to what refreshrate and slowdown? I mean I would love to play all my 24fps on 24Hz, all my 25fps on 24Hz (PAL slowed down to original pitch) and 30fps on 60Hz. That would be awesome (if anyone understands what I'm talking about... Smile )

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Nazgulled Offline
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Post: #333
ashlar Wrote:And thank god for that! You'd be then listening to the original pitch in 99% of the cases where movies are concerned.
What do you mean by this?

But this conversion ("25fps PAL video to 24fps", is not necessary because, at least for my TV, I can play PAL movies in 50Hz, right?
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dpassent Offline
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Post: #334
Ok. Let the lecture begin... Smile

Films are originally shot in 24fps (almost, lets assume this). To play them smoothly on PAL tvs, you have to convert 24fps to 25fps (to bring the 2:2 pulldown for 50Hz, which is PAL frequency). The easiest and cheapest way to do this is to playback 24fps film at 25fps framerate (speed it up a little). This results in higher pitched voices and shorter running time of the movie. Check this webpage to see what I mean:

http://www.schmidt-web.info/malte/english.html

DP
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Nazgulled Offline
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I was talking about videos in 25fps not 24fps. My TV also handles 23Hz/24Hz, no need to convert anything. They are not the majority, I know, but know and then a movie in 25fps comes up and it would be enough to play it at 25Hz/50Hz, right?

Or would I still need the work being done by bobo1on1 in the "xbmc-smoothvideo" branch?
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ashlar Offline
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Post: #336
Nazgulled, it depends on your sources. But, for instance, most movie DVDs in PAL regions are artificially accelerated to 25fps, from the original 24fps. In those cases, you might want to play them back at 24fps, restoring the original pitch of voices, soundtrack, etc.
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bobo1on1 Offline
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Post: #337
Nowadays I believe the pitch is corrected with a 24 to 25 conversion, but there's no way of knowing that unless you have the ntsc dvd, and then you might as well use pulldown on that and watch it at 24 fps.
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dpassent Offline
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Post: #338
you would be surprised how very few dvds are timestreched instead of pitchshifted. even today majority of PAL dvds are simply played faster

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bobo1on1 Offline
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Post: #339
In that case, they will play just fine at 24 fps, when I implement the resampler.
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Nazgulled Offline
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Post: #340
But, what will happen exactly?

I mean, let's say I put a PAL DVD in my drive and start playing the movie. Will you simply detect that the DVD is played at 25fps and assume that it should be played at 24fps and forcibly apply your resample thing?

I guess that question can be resumed to: how will you know if a PAL DVD was originally converted from 24fps?

Either way, I mostly watch digital files and those normally are 23,976fps or 24fps, so, no problem here. But I buy a DVD (PAL cause I'm from Europe) once a in while for a movie I really like.

But I really can't see the benefit and I really wanted to understand it cause I want to have the best playback possible. I mean, let's say I play an MKV video file and this file is 24fps. Wouldn't the "adjust refresh rate" option suffice to playback that video the smoothest way possible? If the video plays at 24fps, the screen refresh rate is 24Hz, it's all good, right? Or do I still need the work you are doing in the "smoothvideo" branch? I could understand this for videos with 23.976 which 24Hz or even 23Hz are not a perfect match, and your work could prove useful in this situation, but in a 24fps/24Hz situation, is there any benefit?

I'm not saying your work is not appreciated and it doesn't serve any porpuse. Any work to improve anything XBMC is appreciated and thank all the developers that invested their time on this great application. I just want to make that clear. And I'm sorry for all of these questions too.. I just want to understand all this...
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ashlar Offline
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Post: #341
bobo1on1 Wrote:In that case, they will play just fine at 24 fps, when I implement the resampler.
I know I already wrote an enthusiastic message when you first announced XBMC "reclock-like" functionalities but... again, thanks a bunch. This is a huge step in the right direction.

Now we "just" need custom shaders and avisynth filters for DVDplayer and XBMC will rule the HTPC world, as it rightfully should. Big Grin (is avisynth Windows only?).

Edit: the second part of this is, mainly, a joke. In the past few months XBMC has made so many steps in the right direction that I can't even count them. I'm sure a lot more will come, but I'm in no hurry.
(This post was last modified: 2009-02-25 18:55 by ashlar.)
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bobo1on1 Offline
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Post: #342
Nazgulled Wrote:But, what will happen exactly?

I mean, let's say I put a PAL DVD in my drive and start playing the movie. Will you simply detect that the DVD is played at 25fps and assume that it should be played at 24fps and forcibly apply your resample thing?

I guess that question can be resumed to: how will you know if a PAL DVD was originally converted from 24fps?

Well, you won't know, so any pal dvd will play at 24 fps, but only if your refreshrate is a multiple of 24 hertz, set it to a multiple of 25 hertz and it will play at 25 fps.
You can also adjust the maximum speed change, you can set it to 0% if you want, but remember that the refreshrate and fps are both rounded, so 23.976 fps will be treated as 24 fps and 59.94 hertz will be treated as 60 hertz.

Quote:Either way, I mostly watch digital files and those normally are 23,976fps or 24fps, so, no problem here. But I buy a DVD (PAL cause I'm from Europe) once a in while for a movie I really like.

But I really can't see the benefit and I really wanted to understand it cause I want to have the best playback possible. I mean, let's say I play an MKV video file and this file is 24fps. Wouldn't the "adjust refresh rate" option suffice to playback that video the smoothest way possible? If the video plays at 24fps, the screen refresh rate is 24Hz, it's all good, right? Or do I still need the work you are doing in the "smoothvideo" branch? I could understand this for videos with 23.976 which 24Hz or even 23Hz are not a perfect match, and your work could prove useful in this situation, but in a 24fps/24Hz situation, is there any benefit?

The problem with playing video on a computer is that the system clock is used to play the video at the correct speed, because of several reasons, this clock as an awful lot of jitter and is also slightly off from the videoclock, thus causing jerky playback.
What I did is sync the playback to the videoclock, so now the audio has to handle all the jitter (which it can do just fine), so providing your computer is fast enough (which it is) you get perfectly smooth playback.

Quote:I'm not saying your work is not appreciated and it doesn't serve any porpuse. Any work to improve anything XBMC is appreciated and thank all the developers that invested their time on this great application. I just want to make that clear. And I'm sorry for all of these questions too.. I just want to understand all this...
No problem Smile
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Nazgulled Offline
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Post: #343
bobo1on1 Wrote:Well, you won't know, so any pal dvd will play at 24 fps, but only if your refreshrate is a multiple of 24 hertz, set it to a multiple of 25 hertz and it will play at 25 fps.
You can also adjust the maximum speed change, you can set it to 0% if you want, but remember that the refreshrate and fps are both rounded, so 23.976 fps will be treated as 24 fps and 59.94 hertz will be treated as 60 hertz.
Basically, this means that, it doesn't matter if the DVD is 24fps or 25fps, as long as I have the "adjust refresh rate" option enabled, my DVDs will all playback at the proper refresh rate?

But this still leaves me to the same question... What if, one of these PAL DVDs (25fps) were actually converted from 24fps? There's no way to tell that right? So, if you don't know, the movie is 25fps and the refresh rate is 25Hz, the work you are doing won't do anything to this specific playback, right?

bobo1on1 Wrote:The problem with playing video on a computer is that the system clock is used to play the video at the correct speed, because of several reasons, this clock as an awful lot of jitter and is also slightly off from the videoclock, thus causing jerky playback.
What I did is sync the playback to the videoclock, so now the audio has to handle all the jitter (which it can do just fine), so providing your computer is fast enough (which it is) you get perfectly smooth playback.
So, what you are saying is that the system clock and video clock are not always in sync and your work is to fix that, correct?

And just so I get the whole picture here, by system clock you are referring to the clock speed of the CPU and by video clock, to the clock speed of the GPU or something else? If this is correct, well, I got say I never thought this could be such an issue for perfect smooth playback... I always thought the problem was only a matter of video fps and screen refresh rate...
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Hitcher Offline
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Post: #344
My head hurts.
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bobo1on1 Offline
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Nazgulled Wrote:Basically, this means that, it doesn't matter if the DVD is 24fps or 25fps, as long as I have the "adjust refresh rate" option enabled, my DVDs will all playback at the proper refresh rate?

But this still leaves me to the same question... What if, one of these PAL DVDs (25fps) were actually converted from 24fps? There's no way to tell that right? So, if you don't know, the movie is 25fps and the refresh rate is 25Hz, the work you are doing won't do anything to this specific playback, right?
If your refreshrate is 25 hertz and the dvd is 25 fps, it will play at 25 fps, but it will play a lot smoother, the effect can especially be noticed on pans (unfortunately for me and fortunately for everyone else I notice it all the time).
Quote:So, what you are saying is that the system clock and video clock are not always in sync and your work is to fix that, correct?

And just so I get the whole picture here, by system clock you are referring to the clock speed of the CPU and by video clock, to the clock speed of the GPU or something else? If this is correct, well, I got say I never thought this could be such an issue for perfect smooth playback... I always thought the problem was only a matter of video fps and screen refresh rate...

The problem exists on many levels, and two unsynchronized clocks is one of em, imagine having two (cheap)watches, even if you synchronize them every day, they will never show the exact same time.
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