ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)" < /dev/null 2> /dev/null

youtube-dl is up-to-date (2018.07.21)

WARNING: KOID24005817AA: malformed AAC bitstream detected. Install ffmpeg or avconv to fix this automatically.

brew install ffmpeg --with-fdk-aac --with-ffplay --with-freetype --with-libass --with-libquvi --with-libvorbis --with-libvpx --with-opus --with-x265

brew upgrade libav
Error: libav 12.3 already installed

brew update && brew upgrade ffmpeg
Already up-to-date.
Error: ffmpeg 4.0.2 already installed

youtube-dl --sub-format srt https://tv.nrk.no/serie/den-blaa-planeten/sesong/2/episode/1/avspiller
[NRKTVEpisode] den-blaa-planeten/sesong/2/episode/1: Downloading webpage
[NRK] KOID24005217: Downloading mediaelement JSON
[NRK] KOID24005217: Downloading f4m manifest
[NRK] KOID24005217: Downloading m3u8 information
[download] Downloading playlist: Den blå planeten 1:7
[NRK] playlist Den blå planeten 1:7: Collected 1 video ids (downloading 1 of them)
[download] Downloading video 1 of 1
[download] Den blå planeten 1_7-KOID24005217AA.mp4 has already been downloaded
[download] 100% of 866.34MiB
[ffmpeg] Fixing malformed AAC bitstream in "Den blå planeten 1_7-KOID24005217AA.mp4"
ERROR: av_interleaved_write_frame(): Invalid argument

 youtube-dl --all-subs https://tv.nrk.no/serie/den-blaa-planeten/sesong/2/episode/3/avspiller