# How to Configure the Bold-Overlay Subtitle Style for Various Video Types Using video-use

> Learn how to configure the bold-overlay subtitle style for video-use. Customize subtitle appearance using constants or environment variables for diverse video types.

- Repository: [Browser Use/video-use](https://github.com/browser-use/video-use)
- Tags: how-to-guide
- Published: 2026-07-08

---

**The bold-overlay subtitle style in video-use is controlled by the `SUB_FORCE_STYLE` constant in [`helpers/render.py`](https://github.com/browser-use/video-use/blob/main/helpers/render.py), which defaults to a high-contrast, two-word uppercase format and can be customized by editing the constant or using environment variables to suit different video types.**

The `browser-use/video-use` repository provides a streamlined video rendering pipeline that applies subtitles as a final FFmpeg filter pass. Configuring the **bold-overlay** subtitle style allows you to maintain consistent readability across different video types while adapting the aesthetic for specific content needs.

## Understanding the Bold-Overlay Style

### Default Style Characteristics

The default `bold-overlay` style defined in [`helpers/render.py`](https://github.com/browser-use/video-use/blob/main/helpers/render.py) produces terse, two-word **UPPERCASE** captions using Helvetica 18 Bold with a white-on-outline font scheme. This configuration includes a vertical margin of 35 pixels, ensuring subtitles remain legible on mobile screens without obscuring critical video content.

### Technical Implementation

According to the source code in [`helpers/render.py`](https://github.com/browser-use/video-use/blob/main/helpers/render.py), the style string is passed directly to the FFmpeg `subtitles` filter via the `force_style` option. As documented in [`SKILL.md`](https://github.com/browser-use/video-use/blob/main/SKILL.md), this filter operates as the **last** processing step in the render pipeline, guaranteeing that subtitles appear above all overlays and video effects.

## Configuring Subtitle Styles for Different Video Types

### Editing the SUB_FORCE_STYLE Constant

To permanently change the subtitle appearance for a specific video category, modify the `SUB_FORCE_STYLE` constant at the top of [`helpers/render.py`](https://github.com/browser-use/video-use/blob/main/helpers/render.py). For example, to create a cinematic documentary style with lower-case text and increased margins:

```python

# helpers/render.py

SUB_FORCE_STYLE = (
    "FontName=Arial,FontSize=24,"
    "PrimaryColour=&H00FFFFFF&,OutlineColour=&H00000000&,"
    "BorderStyle=1,MarginV=50,Bold=0,Italic=0"
)

```

### Using Environment Variables for Runtime Overrides

For temporary style changes without modifying source code, patch [`helpers/render.py`](https://github.com/browser-use/video-use/blob/main/helpers/render.py) to read from an environment variable:

```python
import os
SUB_FORCE_STYLE = os.getenv("VIDEO_USE_SUB_STYLE", "bold-overlay")

```

Then invoke the renderer with a custom style for specific video types:

```bash
VIDEO_USE_SUB_STYLE="FontName=Times,FontSize=22,PrimaryColour=&H00FFCC00&,MarginV=40" \
python helpers/render.py edl.json -o output.mp4 --build-subtitles

```

### Creating Video-Type-Specific EDLs

Edit-decision-list (EDL) files allow you to route different video types through the same rendering pipeline while using distinct subtitle sources. The [`helpers/transcribe.py`](https://github.com/browser-use/video-use/blob/main/helpers/transcribe.py) module generates `.srt` files that feed into this pipeline. Since [`helpers/render.py`](https://github.com/browser-use/video-use/blob/main/helpers/render.py) applies the global `SUB_FORCE_STYLE` to whichever `.srt` file the EDL references, you can maintain separate EDLs for tutorials, promos, and documentaries while customizing the style constant between batch jobs.

## CLI Commands for Subtitle Rendering

The [`render.py`](https://github.com/browser-use/video-use/blob/main/render.py) script accepts several flags to control subtitle generation:

- `--build-subtitles`: Generates a master subtitle file from transcriptions and applies the configured style
- `--no-subtitles`: Skips subtitle processing entirely
- Omitting both flags: Uses existing subtitle files without rebuilding

Example workflow for a tutorial video:

```bash

# Build subtitles with custom style (set via env var or edited constant)

python helpers/render.py tutorial_edl.json -o tutorial.mp4 --build-subtitles

```

Example for a final export without captions:

```bash
python helpers/render.py final_edl.json -o final.mp4 --no-subtitles

```

## Verifying Subtitle Placement

After rendering, use [`helpers/timeline_view.py`](https://github.com/browser-use/video-use/blob/main/helpers/timeline_view.py) to visualize the final output and confirm that the **bold-overlay** style appears correctly above video content without obstruction.

## Summary

- The **bold-overlay** style is defined by the `SUB_FORCE_STYLE` constant in [`helpers/render.py`](https://github.com/browser-use/video-use/blob/main/helpers/render.py)
- By default, it uses Helvetica 18 Bold, white text with black outline, and 35px vertical margins
- Subtitles are always applied last in the FFmpeg pipeline, as enforced by hard rule 1 in [`SKILL.md`](https://github.com/browser-use/video-use/blob/main/SKILL.md)
- Customize styles by editing the constant, using environment variables, or maintaining separate EDL files for different video types
- Use `--build-subtitles` to generate captions from transcriptions or `--no-subtitles` to disable them

## Frequently Asked Questions

### What is the default bold-overlay style in video-use?

The default style specified in [`helpers/render.py`](https://github.com/browser-use/video-use/blob/main/helpers/render.py) uses a two-word, uppercase format with Helvetica 18 Bold font, white primary color, black outline, and 35-pixel vertical margins. This creates high-contrast captions optimized for quick readability on mobile devices.

### How do I change the subtitle font for tutorial videos?

Edit the `SUB_FORCE_STYLE` constant in [`helpers/render.py`](https://github.com/browser-use/video-use/blob/main/helpers/render.py) to specify your desired font properties, or set the `VIDEO_USE_SUB_STYLE` environment variable if you have patched the file to support runtime overrides. For tutorial content, consider reducing font size and switching to sentence case for a softer aesthetic.

### Can I disable subtitles entirely when rendering?

Yes. Pass the `--no-subtitles` flag to [`helpers/render.py`](https://github.com/browser-use/video-use/blob/main/helpers/render.py) to skip subtitle processing completely. This is useful for generating clean preview versions or when final captions will be added in post-production.

### Why are subtitles applied last in the FFmpeg pipeline?

According to [`SKILL.md`](https://github.com/browser-use/video-use/blob/main/SKILL.md), subtitles must be the final filter operation to ensure they appear above all video overlays and effects. This hard rule prevents graphical elements from obscuring text, maintaining accessibility and readability as defined by the `SUB_FORCE_STYLE` configuration.