encoding-guide

Baby’s First Script

Congratulations on setting up your encoding environment! Now it’s time to write and run your first VapourSynth script. This will involve loading a video source, applying basic filters, and preparing the file for encoding.

What is VapourSynth?

VapourSynth is a scripting-based video processing tool. It allows you to load, filter, and manipulate video files before encoding. VapourSynth uses Python for scripting, so familiarity with basic Python syntax will help.

Writing Your First Script

Step 1: Create a New Script File

Open a text editor (e.g., Notepad++, Visual Studio Code, or Sublime Text).
Save a new file with the .vpy extension, such as first_script.vpy.

Step 2: Load Your Video Source

To load a video source, use one of VapourSynth’s core plugins, such as ffms2 or LSMASHSource. Here’s a basic example:

import vapoursynth as vs
core = vs.core

# Load video source
clip = core.ffms2.Source("example.mkv")

# Output the video
clip.set_output()

Step 3: Apply Basic Filters

Filters enhance the video by addressing artifacts or resizing the resolution. For example:

Crop and Resize:

# Crop 10 pixels from each side and resize to 1280x720
clip = core.crop(clip, left=10, right=10, top=10, bottom=10)
clip = core.resize.Bilinear(clip, width=1280, height=720)

Deband:

# Apply debanding to smooth gradients
clip = core.f3kdb.Deband(clip, range=15, y=64, cb=64, cr=64)

Denoise:

# Apply light denoising to remove noise
clip = core.knlm.KNLMeansCL(clip, d=1, a=2, h=1.2)

Step 4: Save and Preview Your Script

Save the script file.
Preview it using a media player like mpv or by piping the script to ffplay:
```
vspipe --y4m first_script.vpy - | ffplay -
```

Understanding the Script

Here’s a complete example of a basic VapourSynth script:

import vapoursynth as vs
core = vs.core

# Load the video
clip = core.ffms2.Source("example.mkv")

# Apply basic filters
clip = core.crop(clip, left=10, right=10, top=10, bottom=10)  # Crop edges
clip = core.resize.Bilinear(clip, width=1280, height=720)     # Resize
clip = core.f3kdb.Deband(clip, range=15, y=64, cb=64, cr=64)  # Deband

# Output the video
clip.set_output()

Running the Script

Preview the Script: Run the following command to preview your script:
```
vspipe --y4m first_script.vpy - | ffplay -
```

Encode the Video: To encode the video, pipe the output into an encoder like x264 or x265:

vspipe first_script.vpy - | x264 --demuxer y4m --preset placebo --level 41 --crf 16.9 --me umh --rc-lookahead 250 --profile high --deblock -2:-1 --chroma-qp-offset -1 --qcomp 0.70 --aq-mode 3 --aq-strength 0.80 --psy-rd 1.00:0 -o output.h264 -

Troubleshooting Tips

Error Loading Plugins: Ensure that VapourSynth plugins like ffms2 are installed correctly.
Video Not Playing: Double-check the file path and format of your source file.
Filters Not Working: Verify that the required filters are installed and correctly referenced in the script.

Conclusion

You’ve written and executed your first VapourSynth script! This foundational knowledge prepares you for more advanced filtering and encoding workflows. In the next section, we’ll explore filtering techniques in depth.