mediapy.write_video() fails with libx265 and qp parameter in gradio_demo Describe the issue

Bug Report: mediapy.write_video() fails with libx265 and qp parameter in gradio_demo Describe the issue When running python -m gradio_demo.app locally to annotate video points via the web UI, the app crashes after selection with a BrokenPipeError followed by a RuntimeError, pointing to a problem with mediapy.write_video().
Reproduction steps

Start the app with:
python -m gradio_demo.app
Open the app in browser, annotate points.
The following output appears in terminal:

What I tried
I verified my FFmpeg version supports libx265 and -qp

Manually running ffmpeg works just fine:

I tried modifying app.py to use:
mediapy.write_video(
video_file_path,
painted_video,
fps=video_fps,
codec='libx265',
qp=28,
encoded_format='yuv420p',
ffmpeg_args=['-preset', 'medium']
)
But I still get the same error.
Expected behavior

The video should be written to disk using libx265 with QP encoding without any crash.

Environment

OS: Ubuntu (inside container)

Python: 3.10

Mediapy: latest (as installed with the project)

FFmpeg: 7.0.2 (static build) with --enable-libx265

Additional context

From looking into the source code, it seems like mediapy is failing to correctly pass -qp when libx265 is specified. This results in a broken pipe when writing video, possibly due to an invalid command construction passed to ffmpeg under the hood.

What would help

A fix in mediapy or a recommended way to safely pass -qp to ffmpeg through mediapy.write_video() — or guidance on how to bypass mediapy safely while staying inside the gradio app.

Thank you for the great tool and your help!

Start by running `python -m gradio_demo.app` and reproducing the crash after annotating points. Read the `app.py` call to `mediapy.write_video()` and compare its arguments with the working manual FFmpeg command; done means the annotated video is written with libx265 and QP encoding without BrokenPipeError or RuntimeError.

Written by the indexing model from the issue text.