Interactive Pre-Filter Zoom (VLC-style) with Script Control

[mstreurman]

Expected behavior of the wanted feature

Summary

Request for a true source-region zoom mechanism in mpv that operates before the video filter chain, enabling interactive zoom/pan that behaves like VLC’s “interactive zoom” while remaining fully compatible with mpv’s advanced rendering pipeline (HDR, shaders, VPP, etc.).

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Problem

Current mpv zoom mechanisms:

• video-zoom
• video-pan-x/y
• video-crop

all operate at the VO/display stage, not on the source frame before filtering.

This leads to:

• zoom being applied after scaling, filtering, and shader processing
• effectively magnifying an already processed frame
• visible quality degradation compared to crop + resample approaches

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Desired Behavior

Introduce a zoom system that behaves as:

decode
→ select source region (interactive crop)
→ apply video filters (e.g. d3d11vpp, scaling)
→ apply shaders (libplacebo)
→ display

Instead of current behavior:

decode
→ filters
→ shaders
→ display
→ then zoom/pan (display transform)

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Key Requirements

1. Pre-filter crop/zoom stage

• Ability to define a dynamic crop region of the source frame
• This crop should occur before vf filters, including:
  • d3d11vpp
  • scaling filters
  • tone mapping / HDR processing

2. Interactive control (scriptable)

Expose the crop/zoom region via properties accessible from Lua.

Example (conceptual):

video-source-crop-x
video-source-crop-y
video-source-crop-w
video-source-crop-h

or normalized:

video-source-center-x
video-source-center-y
video-source-zoom

These should be:

• writable at runtime
• fast enough for continuous updates (mouse drag)

3. GPU-friendly implementation

• Should integrate cleanly with hardware paths:

  • d3d11vpp
  • vaapi
  • nvdec / CUDA
  • vo=gpu-next / libplacebo

• Must avoid:

  • full filter graph rebuilds per frame
  • expensive CPU-side reconfiguration

4. Maintain full pipeline compatibility

Must work correctly with:

• HDR tone mapping
• custom shaders (glsl-shaders)
• scaling algorithms
• existing vf chains

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Motivation / Use Case

Modern mpv setups often include:

• hardware scaling (e.g. Intel VPP)
• multi-pass shader pipelines
• HDR processing
• advanced playback (streams, URLs, capture)

In these setups, current zoom:

• breaks visual fidelity
• feels inferior to VLC’s interactive zoom
• cannot leverage the existing high-quality pipeline

VLC’s zoom works because it:

• crops source region
• resamples it through its pipeline
• keeps interaction smooth and visually consistent

mpv currently lacks an equivalent mechanism.

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Why existing solutions are insufficient

video-zoom

• display-space scaling only
• does not re-run filters on the selected region

video-crop

• VO-side crop, not pre-filter
• not suitable for interactive updates

dynamic vf=crop

• requires filter chain updates
• too heavy for real-time interaction

shaders

• operate post-filter
• cannot move processing earlier in the pipeline

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Proposed Direction (non-binding)

Any of the following would satisfy the requirement:

• a dedicated pre-filter crop stage
• a hardware-accelerated crop region selection
• a libplacebo-integrated source-region sampling control

As long as:

• it happens before filters
• it is scriptable
• it supports real-time interaction

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Additional Notes

This feature would enable:

• true VLC-style zoom in mpv
• higher-quality inspection workflows
• better usability for high-resolution content
• improved integration with advanced pipelines already present in mpv

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Conclusion

mpv already provides one of the most powerful playback pipelines available.

This feature would fill a key gap by enabling interactive source-region zoom that fully leverages that pipeline instead of bypassing it.

Alternative behavior of the wanted feature

No response

Log File

No response

Sample Files

No response