[FFmpeg-user] Is there a way to re-encode an inefficiently encoded file without losing quality and reducing file size?

[Bruce Gavin]

 Every time you transcode, you lose more quality, same as making a VHS to VHS tape copy.

If space is an issue, buy a Series 40 nVidia card that supports AV1 encoding.
Transcode your blu-ray source directly to AV1 for the smallest file at the highest quality.

True lossless file sizes are FAR larger than those found on a blu-ray, which are H264 encoded.

    On Saturday, September 30, 2023 at 04:51:30 PM PDT, MediaMouth <communque at gmail.com> wrote:  
 
 What about using a hash to check your existing against your possibly new / possibly matching file.  If it's a match don't run ffmpeg on it. Assuming i'm understanding what you're trying to achieve, it would seem better practice not to touch the file with ffmpeg when you can avoid it.  

> On Sep 30, 2023, at 16:43, Stéphane Archer <archerstephane at gmail.com> wrote:
> 
> Let's say you have a video file encoded with high bitrate with the
> ultra-fast preset in H.264 because you couldn't afford CPU at that time.
> Now you have a huge file mostly because it was encoded quickly.
> 
> You are now two days later with access to a good CPU and GPU.
> 
> If you re-encode that file to save space then you are going to lose quality
> because even AV1 with a high bitrate is lossy (and you want to reduce that
> high bitrate)
> 
> Otherwise, you can try transcoding using lossless compression but during my
> testing, this is making the file way bigger no matter what I tried.
> 
> So basically, I can lose quality, or keep the big original file...
> Do you know a better way? Is there a way to re-encode that inefficiently
> encoded file without losing quality and reducing file size?
> 
> Best regards
> 
> Stéphane Archer
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