_ffmpeg.ps1

#

merge.ps1

1..56 `
| %{ "_$($_.ToString().PadLeft(2, '0')).mp4" } `
| &{
	Begin {
		$filter = ''
		$files  = @()
	}
	Process {
		$filter += "[$($files.Count / 2):0] [$($files.Count / 2):1] "
		$files  += '-i',$_
	}
	End {
		& 'C:\Program Files\ffmpeg\bin\ffmpeg.exe' `
			$files `
			-fps_mode       vfr `
			-filter_complex "${filter}concat=n=$($files.Count / 2):v=1:a=1 [v] [a]" `
			-map            '[v]' `
			-map            '[a]' `
			-vcodec         libx264 `
			-crf            10 `
			___720_10.mp4
	}
}

mergeAudio.ps1

. ~/async.ps1

gci -File `
| %{
	if ($_.Name -match '^(\d+)\.mp4$') {
		$Matches[1]
	}
} `
| Async `
	-Func { Process {
		&'C:\Program Files\ffmpeg\bin\ffmpeg.exe' `
			-i "$_.mp4" `
			-filter_complex '[0:a:0][0:a:1]amix=2:weights=0.75 2[aout]' `
			-map '0:V:0' `
			-map '[aout]' `
			-c:v copy `
			"_$_.mp4"
	} }

upscaleMerge.ps1

1..56 `
| %{ "_$($_.ToString().PadLeft(2, '0')).mp4" } `
| &{
	Begin {
		$files = @()
		$lines = ''
		$v     = ''
		$a     = ''
	}
	Process {
		$files += '-i',$_
		$lines += "movie=$_, scale=1920:1080 [v$($files.Count / 2)] ; amovie=$_ [a$($files.Count / 2)] ; "
		$v     += " [v$($files.Count / 2)]"
		$a     += " [a$($files.Count / 2)]"
	}
	End {
		& 'C:\Program Files\ffmpeg\bin\ffmpeg.exe' `
			$files `
			-fps_mode       vfr `
			-filter_complex "$lines$v concat=n=$($files.Count / 2):v=1:a=0 [outv] ;$a concat=n=$($files.Count / 2):v=0:a=1 [outa]" `
			-map            '[outv]' `
			-map            '[outa]' `
			-vcodec         libx264 `
			-crf            10 `
			_.mp4
	}
}

rotate &'C:\Program Files\ffmpeg\bin\ffmpeg.exe' -i .\_.mp4 -vf transpose=1 __.mp4

first 10s of youtube vid yt_dlp --downloader ffmpeg --downloader-args "ffmpeg:-t 10" "https://www.youtube.com/watch?v=abcdef"

cut 15 to 55s out of video ffmpeg' -i _.mp4 -vf "select='not(between(t,15,55))', setpts=N/FRAME_RATE/TB" -af "aselect='not(between(t,15,55))', asetpts=N/SR/TB" .\__.mp4

audio *= 10 ffmpeg -i _.MOV -filter:a 'volume=10' .\__.mp4

transpose=0 90° counter-clockwise and vertical flip (default)
transpose=1 90° clockwise
transpose=2 90° counter-clockwise
transpose=3 90° clockwise and vertical flip

centre and pad to size
-vf "scale=1920:1080:force_original_aspect_ratio=decrease,pad=1920:1080:(ow-iw)/2:(oh-ih)/2,setsar=1"