Enable CTL and Shaping Using libfribidi in FFmpeg

This article provides a quick guide on how to enable Complex Text Layout (CTL) and bidirectional (BiDi) text shaping in FFmpeg using the libfribidi library. You will learn how to configure and compile FFmpeg with the necessary dependencies and how to apply the drawtext filter to correctly render languages like Arabic, Hebrew, Persian, and Urdu on your videos.

Step 1: Compile FFmpeg with libfribidi Support

To use libfribidi for text shaping and CTL, you must compile FFmpeg from source with the library enabled. FFmpeg does not enable this by default.

First, ensure you have the development libraries for fribidi, freetype (required for drawing text), and optionally harfbuzz (for advanced glyph shaping) installed on your system.

On Debian/Ubuntu-based systems, run:

sudo apt-get install libfribidi-dev libfreetype6-dev libharfbuzz-dev

When configuring your FFmpeg build, you must explicitly pass the compile flags to enable these libraries. Run the configure script with the following options:

./configure --enable-gpl --enable-libfreetype --enable-libfribidi --enable-libharfbuzz

After configuring, compile and install FFmpeg:

make -j$(nproc)
sudo make install

Step 2: Verify libfribidi Integration

To confirm that your FFmpeg installation successfully includes libfribidi, run the following command in your terminal:

ffmpeg -version

Look at the configuration section in the output. You should see --enable-libfribidi in the list of enabled configuration options.

Step 3: Render CTL and BiDi Text Using drawtext

Once FFmpeg is compiled with libfribidi support, the drawtext video filter will automatically detect and process bidirectional and complex text layouts. You do not need to pass extra parameters to force shaping; libfribidi handles the text reordering and shaping seamlessly in the background.

Use the following basic command structure to overlay right-to-left (RTL) or complex text onto a video:

ffmpeg -i input.mp4 -vf "drawtext=fontfile=/path/to/supported-font.ttf:text='שלום עולם':fontcolor=white:fontsize=24:x=(w-tw)/2:y=(h-th)/2" -codec:a copy output.mp4

Key Considerations for Success:

• Font Selection: Ensure the font specified in fontfile actually supports the Unicode character set of the target language (e.g., using Arial, Amiri, or Noto Sans). If the font lacks the required glyphs, the text will not render correctly despite libfribidi being active.
• UTF-8 Encoding: Ensure your terminal, script, or input text file is saved in UTF-8 encoding so FFmpeg can correctly parse the complex characters.