[FFmpeg-devel] 24 FPS to 23.975 Conversion with Audio

[Steve Rance]

Sorry, yes, that was a typo on my part, but still even with 24*1000/1001 that would give a non-integer/fractional sample rate which ffmpeg will round.
I will locate the correct group.
Thank you.
Steve


-----Original Message-----
From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> On Behalf Of Zhao Zhili
Sent: Wednesday, March 19, 2025 06:05 PM
To: ffmpeg-devel at ffmpeg.org
Cc: ffmpeg-devel at ffmpeg.org
Subject: Re: [FFmpeg-devel] 24 FPS to 23.975 Conversion with Audio


> 在 2025年3月20日，上午3:35，Steve Rance <steverance at outlook.com> 写道：
> 
> Hello developers, my first post, if I have posted to the wrong place 
> please point me in the right direction
> 
> I'm attempting to use ffmpeg to convert 24FPS media to 23.986 - Video is good but the audio slips.

This mailing list is for ffmpeg development, not user support.

There is no such framerate 23.986, it’s 24 * 1000/1001.

> 
> From my research I need a fractional sample rate for the audio. To be precise I need 48000 × (23.976/24) ≈ 47952.047952 Hz. However, since FFmpeg’s asetrate only accepts an integer value, ffmpeg ends up using 47952 exactly. I have tried many if not all of the options available and the result remains the same.
> 
> Here are the slippage rates ...
> Approximately 172.63 samples error per hour Approximately 2.88 samples 
> error per minute.
> Approximately 20.85 seconds must elapse for each 1 sample error.
> Approximately 11 hours and 35 minutes before the audio is one full frame off.
> 
> I'm using Windows and need advice on how I could try to acheive perfect audio sync.
> 
> Thank you for reading.
> Steve
> 
> 
> 
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