Fix -Frames negative range calculation to extract last N frames correctly (off-by-one error), add validation to reject invalid '-%' and '-0' formats with exit code 1, change '%' alone to extract single last frame instead of range, remove duplicate last frame from PNG sequence concat list, update Get-LastFrame.ps1 and Get-Frame.ps1 to clamp out-of-range frame indices instead of erroring and improve error messages with inline stderr output, add -y flag and -- separator to ffprobe calls, replace deprecated

Get-Frame.ps1

@@ -1,13 +1,14 @@
 <#
 .SYNOPSIS
-    Extracts a specific frame of a video file to a PNG image using Get-LastFrame.ps1, requiring -Video and -Frame parameters from that script.
+    Extracts a specific frame of a video file to a PNG image. The extraction is done by Get-LastFrame.ps1, which this script calls with an image path derived from -Video and -Frame.
     The image filename used for the -Image parameter is automatically derived from the -Video filename, with a "-" followed by the "-Frame" value padded with zeros (at least 4 digits, wider numbers are not truncated) inserted before the image file extension (e.g., P01.mp4 for frame 10 becomes P01-0010.png).
 .PARAMETER Video
     Path to the input video file. Can be absolute or relative to current directory.
 .PARAMETER Frame
     0-based frame index to extract. Negative values count from the end:
-    -1 extracts the last frame (default), -2 extracts second-to-last, etc.
-    The resulting frame index is clamped to the valid range (0 to total frames - 1).
+    -1 extracts the last frame, -2 extracts second-to-last, etc.
+    The resulting frame index is clamped to the valid range (0 to total frames - 1): a positive value past the last frame
+    gives the last frame, and a negative value before the first frame gives frame 0.
 #>
 [CmdletBinding(SupportsShouldProcess)]
 param(
@@ -35,8 +36,7 @@ $totalFramesOutput = & ffprobe -v error -select_streams v:0 -count_frames -show_
 $ffprobeExit = $LASTEXITCODE
 
 if ($ffprobeExit -ne 0) {
-    $totalFramesOutput | ForEach-Object { Write-Error $_ }
-    Write-Error ('ffprobe failed to read video file: {0}' -f $VideoPath)
+    Write-Error ('ffprobe failed to read video file: {0}{1}{2}' -f $VideoPath, [Environment]::NewLine, ($totalFramesOutput -join [Environment]::NewLine))
     exit 1
 }
 
@@ -48,19 +48,15 @@ if (-not $totalFrames -or ([string]$totalFrames).Trim() -notmatch '^\d+$') {
 }
 
 $totalFramesInt = [int]([string]$totalFrames).Trim()
+if ($totalFramesInt -lt 1) {
+    Write-Error ('Video has no frames: {0}' -f $VideoPath)
+    exit 1
+}
 $maxFrameIndex = $totalFramesInt - 1
 
 # Resolve frame index (handles negative values that count from the end)
-$frameToExtract = if ($Frame -lt 0) {
-    $calculatedFrame = $totalFramesInt + $Frame
-    [Math]::Max(0, [Math]::Min($calculatedFrame, $maxFrameIndex))
-} else {
-    if ($Frame -gt $maxFrameIndex) {
-        Write-Error ('Frame index {0} is out of range. Valid range: 0 to {1}' -f $Frame, $maxFrameIndex)
-        exit 1
-    }
-    $Frame
-}
+$requestedFrame = if ($Frame -lt 0) { $totalFramesInt + $Frame } else { $Frame }
+$frameToExtract = [Math]::Max(0, [Math]::Min($requestedFrame, $maxFrameIndex))
 
 # Derive the output image path: insert "-XXXX" (zero-padded resolved frame index) before .png extension
 $videoBase = [System.IO.Path]::GetFileNameWithoutExtension($VideoPath)