Powershell / FFMPEG - multiple clips from multiple input videos. Configurable audio/video fade

extract_clips_with_fade.ps1

####
## Config

# FFMPEG
$ffmpegPath = "ffmpeg.exe"
$ffplayPath = "ffplay.exe"
#$isPreview = $true # Uncomment to preview (ffplay) instead of transcoding.


# OUTPUT
$outputFolder = "./transcoded_output"

# TIMES
$video_fade_in_secs = 0
$video_fade_out_secs = 1.5
$audio_fade_in_secs = 2
$audio_fade_out_secs = 6


####
## DATA

# Helper path vars (REPLACE ME)
$color_corrected = "./One Long shot.mp4"
$no_color = "./One Long shot_no color.mp4"
$stabalizer = "./One Long shot_nocolor+_withstabalizer.mp4"

# Clip list (REPLACE ME)
$clips = @(
    @{ 'start' = "00:08"; 'end' = "20";  	'file' = $color_corrected; }
    @{ 'start' = "00:07"; 'end' = "1:20";  	'file' = $color_corrected; }
    @{ 'start' = "01:30"; 'end' = "2:30";	'file' = $color_corrected; }
    @{ 'start' = "01:30"; 'end' = "2:30" ; 	'file' = $no_color; }
    @{ 'start' = "02:47"; 'end' = "4:06"; 	'file' = $no_color; }
)



####
## Helper functions

function parse_seconds($timestr) {
  # Note: does not support fractions for now.

  # check if int passed in (ParseExact with 's' fmt == doesn't work.)
  [int]$secs = $null
  if ([int32]::TryParse($a , [ref]$secs )) {
    return $secs
  }

  $formats = @(
    'ss',
    'm\:s',
    'h\:m\:s'
  )

  foreach ($fmt in $formats) {
    try {
      return [int][datetime]::ParseExact($timestr, "$fmt", $null).TimeOfDay.TotalSeconds
    }
    catch { }
  }
  
  throw "Could not parse_seconds from the timestamp $timestr !"
}


####
## MAIN

New-Item -Path "$outputFolder" -ItemType Directory -Force

foreach ($clip in $clips) {
    $inputFile = $clip['file']
    $startTime = $clip['start']
    $endTime = $clip['end']


    # Colons are problematic for filters + filenames. so get seconds. Also needed for fade calculations later.
    $startTimeSecs = parse_seconds("$startTime")
    $endTimeSecs = parse_seconds("$endtime")
    $durationSecs = $endTimeSecs - $startTimeSecs

    $baseName = [System.IO.Path]::GetFileNameWithoutExtension($inputFile)
    $outputFile = "$outputFolder/${baseName}_${startTimeSecs}-${endTimeSecs}.mp4"

    $fadeOutStart = $endtimeSecs - $fade_in_secs
    $fadeInStart = $startTimeSecs

    ####
    ## build filters
    $has_vfade_in  = $video_fade_in_secs  -gt 0
    $has_vfade_out = $video_fade_out_secs -gt 0
    $has_afade_in  = $audio_fade_in_secs  -gt 0
    $has_afade_out = $audio_fade_out_secs -gt 0

    $vfilter = ""
    $afilter = ""

    if ($has_vfade_in) { $vfilter += "fade=t=in:st=${startTimeSecs}:d=${video_fade_in_secs}" }
    if ($has_afade_in -gt 0) { $afilter += "afade=t=in:st=${startTimeSecs}:d=${audio_fade_in_secs}" }

    if ($has_vfade_in -and $has_vfade_out) { $vfilter += "," }
    if ($has_afade_in -and $has_afade_out) { $afilter += "," }

    if ($has_vfade_out) { $vfilter += "fade=t=out:st=$($endTimeSecs-$video_fade_out_secs):d=${video_fade_out_secs}" }
    if ($has_afade_out) { $afilter += "afade=t=out:st=$($endTimeSecs-$audio_fade_out_secs):d=${audio_fade_out_secs}" }

    ####
    ## Actual command

    echo "Transcoding (time: $startTime -> $endTime, file: $inputFile -> $outputFile)"
    echo "vfilter: $vfilter"
    echo "afilter: $afilter"
    echo "----------------------`n`n`n`n"

    if ($isPreview) {
      & $ffplayPath -i $inputFile -ss "$startTime" -t "$durationSecs" -vf "$vfilter" -af "$afilter" 
    } else {
      & $ffmpegPath -i $inputFile -ss "$startTime" -to "$endTime" -vf "$vfilter" -af "$afilter" "$outputFile"
    }
}