Burning subtitles hangs on Android about ffmpeg-kit

[tanersener]

This issue happens when font directory registered using setFontDirectory includes named pipes created using registerNewFFmpegPipe.

When subtitle burning command is being executed, fontconfig reads all files under the registered font directory as part of the font loading process. However, in this case, font directory also contains named pipes not closed by closeFFmpegPipe. So, fontconfig tries to read named pipes as well. And, since named pipes require someone to write something into the pipe, fontconfig can not read named pipes successfully and wait forever.

There are two wrongs in this case but none of them are ffmpeg-kit bugs.

• An ffmpeg pipe created using registerNewFFmpegPipe is not closed
• Cache directory is used as font directory

Unfortunately, fontconfig scans sub-directories as well. So, creating ffmpeg pipes under a sub-directory of cache does not solve this problem.

The only solution is not to register application cache directory as font directory on Android.

This issue does not happen on Apple platforms, because they use different directories to create pipes and load fonts. Pipes are created under the application cache folder and fonts are loaded from the resource folder. But the same principle must be followed on them too. Application cache directory shouldn't be registered as font directory on iOS/tvOS/macOS. If not it will happen on Apple devices too.