Every video upload ends up as "No preview available". The video file itself is stored and served correctly (remote instances fetch it with HTTP 200), only the poster frame is missing.

The app log shows the thumbnail job failing immediately:

production.ERROR: Unable to load FFMpeg
FFMpeg\Exception\ExecutableNotFoundException: Unable to load FFMpeg
  at vendor/php-ffmpeg/php-ffmpeg/src/FFMpeg/Driver/FFMpegDriver.php:57
[previous] Alchemy\BinaryDriver\Exception\ExecutableNotFoundException:
  Executable not found, proposed : ffmpeg
  at vendor/php-ffmpeg/php-ffmpeg/src/Alchemy/BinaryDriver/AbstractBinary.php:159
→ app/Jobs/VideoPipeline/VideoThumbnail.php(92)

App\Jobs\VideoPipeline\VideoThumbnail .... 156.32ms FAIL

There is no ffmpeg binary in the container at all — which ffmpeg returns nothing and a find / -name ffmpeg -type f turns up no hits. Pixelfed requires it for video thumbnails, so as far as I can tell the package is missing a dependency.