Build against ffmpeg 5 fails

The build fails against ffmpeg 5: https://martchus.no-ip.biz/shares/45kl6j3l4k523424lk24j5l45kjk4l/subtitlecomposer/pkg/build.log

I haven't seen any patches on master or a dedicated branch so far so I'm opening an issue. Maybe I can come up with a patch myself later.