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

skill/Get-Frame.md

@@ -8,7 +8,7 @@ Extracts a specific frame of a video file to a PNG image by calling [Get-LastFra
 - **`-Frame`** (required): 0-based frame index to extract.
     - Positive values: Direct frame index (e.g., `0` = first frame, `100` = frame 100)
     - Negative values: Count from the end (e.g., `-1` = last frame, `-2` = second-to-last)
-    - Values are automatically clamped to the valid range (0 to total frames − 1)
+    - Values are automatically 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
 
 ## Image Filename Derivation