Video-Processing-Scripts/video-processing-scripts/Stitch-InBetween.md

Stitch-InBetween.ps1

Generates interpolated in-between frames between two images using RIFE and encodes them into a video.

Synopsis

Uses rife-ncnn-vulkan to interpolate frames between a first and last image, then encodes the result into an H.264 video using ffmpeg.

The script:

1. Validates that the input image files exist
2. Creates a dedicated temporary directory for input images
3. Copies the first and last images to the dedicated temp directory
4. Runs rife-ncnn-vulkan.exe to generate interpolated frames
5. Filters the generated frames to keep only the desired in-between sequence
6. Encodes the remaining frames into a video at the specified FPS

Parameters

• -First (required): Full or relative path to the first image file (e.g., First.png or D:\Images\First.png)
• -Last (required): Full or relative path to the last image file (e.g., Last.png or D:\Images\Last.png)
• -TempDir (optional): Full absolute path to a temporary directory for intermediate PNG frames. Must end with \. Defaults to a system-generated temp subdirectory. This is separate from the dedicated input temp directory.
• -Frames (required): Number of frames to generate in the output video. Must be greater than 0
• -Video (required): Output video filename. If relative, resolved against current directory
• -FPS (optional): Frames per second for the output video (default: 24)

Frame Generation

The number of frames passed to rife-ncnn-vulkan is computed as:

Count  = 4 + (($Frames - 1) * 2)
EndsAt = Count / 2

After generation, rife-ncnn-vulkan outputs files named %08d.png. The script deletes:

• 00000001.png (copy of the first input image)
• All files with index greater than EndsAt (copy of the last input image and beyond)

Only the true interpolated frames (00000002.png through 00000{EndsAt}.png) are passed to ffmpeg.

Examples

Basic interpolation:

.\Stitch-InBetween.ps1 -First "frame1.png" -Last "frame2.png" -Frames 30 -Video "output.mp4"

Full paths with custom FPS:

.\Stitch-InBetween.ps1 -First "D:\Images\start.png" -Last "D:\Images\end.png" -Frames 60 -Video "result.mp4" -FPS 30

Absolute paths for input and output:

.\Stitch-InBetween.ps1 -First "C:\Work\Frames\A.png" -Last "C:\Work\Frames\B.png" -Frames 24 -Video "D:\Output\clip.mp4"

Custom temp directory:

.\Stitch-InBetween.ps1 -First "A.png" -Last "B.png" -Frames 24 -Video "clip.mp4" -TempDir "D:\Temp\rife\"

Safe Execution

This script supports -WhatIf and -Confirm for safe execution:

• -WhatIf: Simulate the operation without actually generating frames or creating the video. Shows what would be done.
• -Confirm: Prompt for confirmation before clearing temp directory, generating frames, and creating the video.

Simulate without making changes:

.\Stitch-InBetween.ps1 -First "frame1.png" -Last "frame2.png" -Frames 30 -Video "output.mp4" -WhatIf

Prompt before operations:

.\Stitch-InBetween.ps1 -First "frame1.png" -Last "frame2.png" -Frames 30 -Video "output.mp4" -Confirm

Existing Files and Temporary Directory

• -Video: if a file already exists at this path, it is deleted before generation starts. The old file is gone even if the generation fails later. Use -WhatIf to see the deletion first.
• -TempDir: if the folder already exists, everything inside it is deleted recursively before generation starts. Pass a dedicated folder that holds nothing you need. The default is a new folder under the system temporary directory, so no existing file is deleted.
• The input frames are copied to a second temporary folder under the system temporary directory. This folder is deleted after rife-ncnn-vulkan finishes successfully.
• Intermediate frames in -TempDir are deleted as described in Frame Generation.

Notes

• Requires rife-ncnn-vulkan.exe (TNTwise fork, RIFE 4.26) in the system PATH
• Requires ffmpeg in the system PATH
• Requires the RIFE_HOME environment variable pointing to the rife-ncnn-vulkan install directory (the same folder that is on PATH). The script resolves the model directory from %RIFE_HOME%\rife-v4.26.
• Requires the NCNN_GPU_ID environment variable set to the desired GPU device ID passed to rife-ncnn-vulkan via the -g flag:
  • -1 — CPU only (no Vulkan GPU required).
  • 0 — First GPU.
  • 1, 2, etc. — Additional GPUs.
• The script creates a dedicated temporary directory for input images, separate from the -TempDir parameter
• Input images can be located anywhere on the filesystem and are copied to the dedicated temp directory
• The dedicated input temp directory is automatically cleaned up after frame generation
• The output temp directory (-TempDir) is created if it does not exist; its contents are always cleared before each run
• Output codec: libx264, CRF 8, pixel format yuv420p