When the manifest is not downloadable by native downloader, it already is able to detect it and switch to `ffmpeg`. So there doesn't seem to be a reason anymore to use ffmpeg as the preferred downloader
closes #223 Authored by: nao20010128nao Modified from: https://github.com/nao20010128nao/ytdl-patched/blob/9e4a0e061a558cdb05a618e27f47ca0ac56ece94/youtube_dl/extractor/whowatch.py