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[Idea] Avidemux - easy method to slow 25fps footage back to 24, and vice versa
Big Grin 
Found a easy way to speed down PAL/25fps footage (that is correctly sped up from a film source and definitely NOT field blended video, as that would still require some convoluted secret sauce of multiple scripts) without the use for Avisynth (as still cannot figure that out for the life of me  Confused)

Now the catches to this are:

This program renders with lossy codecs, but you can set the quality as high as you want in each codec's settings and get near transparent quality.

If your file has an audio track you want sped up to sync with the video, you can only get the "Film to PAL" box if you render with AAC or AC3 in the "Audio Filters" tab (copy stream with PCM, DTS, or DD Tru HD or Plus will not work and sound garbled). In this case, it is highly recommended to extract your multichannel/lossless audio and bring it into audacity/whatever other audio program you use and change speed/tempo to -4.096 (or the same number but without the - for speeding up 24fps to 25) to render separately and sync to the re timed video manually.

Download the latest version of Avidemux (freeware) http://avidemux.sourceforge.net/download.html

Load up your video, then in the video output column on the left. In order to access filters for what we're going to do, it requires a re-render. Click "Copy" and scroll down to the video codec you want to render in and hit "Configure" to set it's perimeters/bitrate to whatever you like.

Next, go to "Filters" underneath the configure tab and the video filter manager window pops up and should put you at the "Transform" selection of filters. Scroll down to the "Change FPS" filter, top source FPS should be set at "Custom" and the lower would denote the actual frame rate of the source. Since our source is "25fps", leave the top two as is and tick "Destination FPS" and select "23.98". Note: if your 25fps source has some odd interlace or top field/bottom issues, I would try the "Deinterlace" filters after you have the Change FPS filter on and find one that works best (if you do it before, you're gonna have field blended shit). Otherwise, I would deinterlace your 25/50i video in a different program that you're familiar with first. Now, if you want to speed up a 24fps source to 25fps, put 25 in the Destination FPS box and don't do anything else unless you need to have audio in sync which will require a lossy rendering in the next step.

Then press OK and it should show up in the "Active Filters" window and close the filter manager. Next, we're gonna have to render audio too if you do choose to keep the original track in sync. Hit "Copy" and choose the audio codec of your choice and whatever rate you like under "Configure". Next, go to "Filters" and in the audio filters window "Frame Rate" change is set to none. Click the drop down and select "PAL to Film" (or "Film to PAL" if converting 24fps to 25). Now, your files audio sample rate should be ether 48000hz or 44100 if the audio was from a CD or LD. If it's the latter, the you'd have to re-sample it in the tick box to 48000hz or the synced audio will have this weird garbled ghost effect. Note: you can hit the "Shift" check box to shift your track several ms to however you want and can set gain to your choosing. I would not recommend using the mixer tick box, as that's for folding down "untouched" multi channel audio and may cause problems with your sped down or up.

Now in the output format, choose the container you want to render in. I highly recommend "MKV" or "AVI", as all the others may not handle the audio correctly depending on the audio codec used. Click the save floppy icon to select your destination and render away. When your file finishes, you should notice a run time difference in your video compared to the original, in addition to a slight motion change (should be no blended fields) and a pitch change in audio.

I understand this method may not be ideal for those who use Avisynth and such, but this is a easier way to speed up or down footage without any blending/frame judder for those who aren't up to the steep learning curve of AS.
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Another good way to streamline video is to use tsMuxerGUI
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Yes, I sometimes use tsMuxerGUI and it's good for that as well. Only nitpicks are you'd have to re time audio (it only changes the FPS speed of only the video) in post anyway, plus it doesn't take all file forms and codecs as it can get finicky with some of them (program hasn't been updated since 2015, and certainly won't read newer things like H265 and HDR).
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MKVToolnix also can change video's framerate without re-encoding. You'll need to work on audio separately though and re-encode it.
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I mean, there are a million different tools and ways to change th framerate of a clip.

My preferred one is the one Colek mentioned, because it is lossless.
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(2018-09-07, 02:07 PM)Colek Wrote: MKVToolnix also can change video's framerate without re-encoding. You'll need to work on audio separately though and re-encode it.

It changes the frame rate only with the .mkv container in the video itself, it does not change, if the video is extracted from the container it will return to the original frame rate, the same happens with the sound and subtitles.
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However, for those who try to restore the original frame rate of European shot on film TV stuff or create PAL versions, MKVToolnix and tsMuxer can't speed up 24 fps to 25 properly without the effects of repeat frames. Avidemux is the only one that I found that can reliably speed up 24 to 25, which was the other reason I brought it up.
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Works a treat! Can it also add film grain?
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Avidmux only has noise removal/degraining filters built in. I suggest ether putting it through some avisynth script in post, or experiment with this method https://fanrestore.com/thread-114-post-4...l#pid48151
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I once used eac3to to slow down both the video and audio of an 1080i50 (film based) Italian Blu-ray, although the resulting 1080p23.976 video stream wasn't fully BD compliant as it would only play correctly on some of my playback devices.
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