FFmpeg: Incorrect Rendering of Arabic Fonts and Diacritical Marks in Drawtext
When working with multimedia files, FFmpeg is a powerful tool that can handle various tasks, such as transcoding, streaming, and manipulating video and audio files. However, rendering Arabic text with diacritical marks in FFmpeg can sometimes be problematic. This article focuses on achieving a looped image-video overlay with Arabic text from the Quran, including text diacritical marks, using a custom font.
Understanding Subtitles and Drawtext in FFmpeg
Subtitles in FFmpeg are typically added using the drawtext filter. This filter allows users to superimpose text on a video, making it an ideal choice for adding translations, captions, or overlays. However, rendering Arabic text with diacritical marks can be challenging due to the complexities of the Arabic language and its associated characters.
Common Issues with Arabic Fonts and Diacritical Marks
Arabic fonts can be inconsistently rendered due to differences in font libraries, operating systems, and software applications. Diacritical marks, which are small characters placed above or below other characters, can be particularly problematic. These marks can appear in the wrong position, be missing, or be replaced by incorrect characters, leading to inaccurate or unreadable text.
Example: Looping Image-Video Overlay with Arabic Text
To create a looped image-video overlay with Arabic text from the Quran, including diacritical marks, follow these steps:
- First, ensure you have the necessary font installed on your system. You can download a suitable Arabic font, such as Amiri, and install it.
- Create a text file containing the Arabic text with diacritical marks. Save the file with the
.assextension (Advanced SubStation Alpha format), which supports complex text rendering. - In the
.assfile, specify the font and character encoding:
[Format]
Fontname=Amiri
Encoding=UTF-8- Add the Arabic text with diacritical marks, ensuring proper formatting:
Dialogue: 0,0:00:00.00,0:00:01.00,default,isvisible,0,0,0,100,100,0,0,0,0, Arabic
بِسْمِ ٱللَّهِ ٱلرَّحْمَٰنِ ٱلرَّحِيمِ
\an2\pos(350,300)
\p1\fs32\c&H800000\b1\t(0,0,0,0,1)
\i0
- Use the following FFmpeg command to loop the image and overlay the Arabic text:
ffmpeg -loop 1 -i image.png -i video.mp4 -vf "drawtext=fontfile=/path/to/Amiri.ttf: \
textfile=arabic_text.ass: fontcolor=white: fontsize=32: box=1: [email protected]: \
boxborderw=5: x=(w-text_w)/2: y=(h-text_h)/2" -c:v libx264 -preset slow -crf 18 \
-c:a copy -shortest output.mp4Rendering Arabic text with diacritical marks in FFmpeg can be challenging, but using the Advanced SubStation Alpha format and specifying the correct font and character encoding can help ensure accurate rendering. By following the steps outlined in this article, you can create a looped image-video overlay with Arabic text from the Quran, including diacritical marks, using a custom font.
References
- FFmpeg Documentation: https://ffmpeg.org/documentation.html
- Advanced SubStation Alpha Format: https://www.matroska.org/technical/specs/subtitle/ass.html
- Amiri Font: https://fonts.google.com/specimen/Amiri