Change frame rate without re-encoding

[Radiorama]

Hello,

I'm new to this forum. I'm starting to use Avidemux after years of using VirtualDubMod because of x264 support.

I can't seem to find a way to change the fps of a video without re-encoding it. This was possible with VirtualDubMod.

I think what I need is the "Change FPS" video filter, but I can't add it to the processing chain if "Output video" is set to "Copy" (filters greyed out).

I apologize if this question has been asked before, but I couldn't find any answer in the forum.

Thanks,
Radiorama.

[eumagga0x2a]

It is impossible only to manipulate the FPS value in the container metadata with Avidemux. Depending on container, this value has purely informational character and doesn't affect playback.

[AQUAR]

What's the purpose being aimed for by wanting to change the FPS of the video?
Speed up, slow down, smooth action etc.

[Radiorama]

I'm muxing a x.264 video with multiple audio tracks. The audio tracks are coded to be in synch when video plays at 25 fps, but the video plays at 23.976 fps. I want the existing frames (i.e. no recoding) to play faster, at 25 fps. This, I think, amounts to changing a parameter in the container.

Anyway, I found that I don't need Avidemux to be able to do this after all. MKVMerge can change the fps of its input video streams.

Thanks AQUAR and eumagga0x2a for your answers.

Best,
Radiorama.

[eumagga0x2a]

I'm muxing a x.264 video with multiple audio tracks. The audio tracks are coded to be in synch when video plays at 25 fps, but the video plays at 23.976 fps. I want the existing frames (i.e. no recoding) to play faster, at 25 fps. This, I think, amounts to changing a parameter in the container.

No, in a MKV this amounts to rewriting timestamps (DTS and PTS) of all frames in the video. In what kind of container is the source video stream stored?

[Radiorama]

It's an mkv file.

[eumagga0x2a]

Then either the video player in use is broken discarding PTS information in video frames if the FPS at the container level contradicts (should be other way round) or the video has been really slowed down to 23.976. Correcting such a case without reencoding is unfortunately not possible with Avidemux.

[Radiorama]

Maybe I failed to explain. The audio and video files I'm muxing come from two different sources: the video and one of the audio tracks are NTSC, the second audio is PAL. I prefer to speed things up rather than slow them down, because PAL audio slowed down to NTSC sounds creepy, so I'm speeding up one audio track (no problem with that) and want to speed up the video as well. I solved my problem during the mux stage through mkvmerge.

Best,
Radiorama.

[AQUAR]

Just a comment:
PAL is speeded up from NTSC material if we are talking US movies.
Meaning you should slow it down so it actually sounds as originally intended.

[WTWASP]

I dunno if this helps, or if it is still relevant some 8 years later(?), but, if you have a video that is in 25fps, the only option is to re-encode at 23.98, AND modify the audio filter to resample the audio "From PAL to FILM". This will keep the sync, but it will also extend the video a little and may sound "slower" - but in my experience with anything encoded in 25 fps, that is not the proper pitch for the audio anyway, and if you have a sharp ear, you can tell anything in 25 fps sounds a little "chipmunky" when compared to a proper 24 fps file.

Anyway, by the sounds of it, you have a perfectly good 23.98 fps video, but the audio tracks are somehow encoded to be in sync with a 25 fps speed, making them OUT of sync with your video, correct?

If so, try half of what I suggested, and COPY your video (as MKV or MP4) as you would, but use the AUDIO FILTER to change audio from "PAL to FILM"  and hopefully that will sync everything up without having to re-encode the video.

Alternatively, if you want to speed up the video to match 25fps audio, then you're looking at re-encoding the video.
I dunno why you would want to speed it up anyway? That "chipmunk" pitch is annoying and ruins a good movie.

I also recommend making sure the sample rate is set to 48 kHz (48000 Hz), if it isn't already, as I have had horrible results with 44kHz after copying/converting. 44kHz is great for audio music (CD) tracks, but not movie audio.