Need a ffmpeg code to convert 2160p x265 60fps to 1080p

[sillymovie]

Hi

Could someone help me with a code for ffmpeg to convert a 2160p video 60fps down to 1080p ?

I used the following code - ffmpeg -i input4kvid.mp4 -vf scale=1920:1080 -c:a copy output1080vid.mp4.

Everything's fine but the output size is down from 60gb to 3 gb!
What do I need to input to get an exact copy of audio and video without losing any quality? Can I change the output from hevc to x264 ?

Secondly could you clarify one more thing if you are aware - does converting a 60fps video down to 23.98 fps mean it'll drop frames and affect the quality of the video ? ANy way around it ?

Many Thanks

[poisondeathray]

Everything's fine but the output size is down from 60gb to 3 gb!

If you want less quality loss, larger filesizes - use a lower crf . The default for libx264 is 23

e.g. -crf 18

What do I need to input to get an exact copy of audio and video without losing any quality?

-c:a copy -c:v copy

This means no scaling. Scaling means you cannot copy

Can I change the output from hevc to x264 ?

-c:v libx264

If you don't specify a codec for mp4, but default ffmpeg right now will select libx264 anyways

Secondly could you clarify one more thing if you are aware - does converting a 60fps video down to 23.98 fps mean it'll drop frames and affect the quality of the video ?

If the original had 60 unique frames /s of real motion, not duplicates, then dropping frames will affect the smoothness of the video because you have fewer motion samples

Re-encoding with lossy codec will negatively affect the quality in terms of each frame quatliy

ANy way around it ?

No

[pandy]

My 2 cents, use zscale instead scale ( or perhaps libplacebo ), it may be required to perform HDR to SDR mapping, side to this you may need to perfrom frame rate conversion (libplacebo?) - i would add also small temporal blur to retain some motion fluidity ( tmix filter )

[sillymovie]

Thanks @poisondeathray and @pandy

Would either of you care to provide me with the code ( I copied the old one from somewhere else) or look at this one if its alright for a copy with no quality loss (I know the size would increase).


ffmpeg -i input4kvid.mp4 -vf scale=1920:1080 -c:a copy -crf 0 preset very slow output1080vid.mp4

It somehow looks clunky! Obviously I'd change the preset and -crf to match the quality I need.

[poisondeathray]

if its alright for a copy with no quality loss (I know the size would increase).


ffmpeg -i input4kvid.mp4 -vf scale=1920:1080 -c:a copy -crf 0 preset very slow output1080vid.mp4

It somehow looks clunky! Obviously I'd change the preset and -crf to match the quality I need.

Nothing about that is a "copy", except for the audio

You lose quality when downscaling

-crf 0 is lossless only for 8bit encoding for libx264. If the source pixel type was 10bit, and you wanted to preserve that with lossless encoding use -qp 0

[sillymovie]

if its alright for a copy with no quality loss (I know the size would increase).


ffmpeg -i input4kvid.mp4 -vf scale=1920:1080 -c:a copy -crf 0 preset very slow output1080vid.mp4

It somehow looks clunky! Obviously I'd change the preset and -crf to match the quality I need.

Nothing about that is a "copy", except for the audio

You lose quality when downscaling

-crf 0 is lossless only for 8bit encoding for libx264. If the source pixel type was 10bit, and you wanted to preserve that with lossless encoding use -qp 0

Thanks for that. Could you possibly write down the correct code for just copy with no quality loss for x264 ? Apologies for the trouble.

[poisondeathray]

Could you possibly write down the correct code for just copy with no quality loss for x264 ?

There is quality loss from downscaling, but no additional quality loss from lossless encoding with -qp 0 for x264 for supported pixel types

ffmpeg -i input4kvid.mp4 -vf scale=1920:1080 -c:v libx264 -qp 0 -c:a copy  output1080vid.mp4

[sillymovie]

@poisondeathray - Much obliged for this!