rtmpdump | rtmpdump is a toolkit for RTMP streams

On Linux/Mac

Some formulae require, or depend on others. You can see which other formulae formula X depends on with:

You have the answer right there in the pip3 output:

Package 'libffi', required by 'gobject-2.0', not found

On macOS, brew install libffi should do it.

(Also, of course, installing anything into the system Python, and not inside a virtualenv, is usually a bad idea.)

On Homebrew unbound is a dependency of gnutls which is a dependency of ffmpeg when using --enable-gnutls (which is used by default in the ffmpeg Homebrew formulae).

gnutls (or openssl, mbedtls, libtls, securetransport) is used in ffmpeg for HTTPS support.

This should fix the problem:

You passed in -f worst. As the name indicates, -f worst will get you the worst video format, with horrible quality and very little support in many applications, including ffmpeg. In short, you got what you asked for.

To get a better file, ask for something else. For instance, if you just want audio (much smaller than picture for most videos), pass in -x.

If you want the best video quality, simply omit -f worst.

If your device can only play a certain resolution (say 300px width), pass in -f 'bestvideo[width<=300]+bestadio/best[width<=300]'.

If your disk space per video is the limit (e.g. 5GB), pass in -f best[filesize<=5GB].

If your device can only play certain formats, specify that format, with acodec, vcodec, container, or simply ext. For instance, -f worstvideo[ext=mp4]+bestaudio/worst[ext=mp4] will get you the worst-quality MP4 file.

Of course, these selectors can be combined, as in -f worst[ext=mp4][filesize<=5GB]. For more information on all of these options, consult the youtube-dl documentation.

There is one hint in the error message:

==> Caveats This formula is keg-only, which means it was not symlinked into /usr/local, because macOS already provides this software and installing another version in parallel can cause all kinds of trouble.

OS X already has curl installed and this binary is used. This version does not work with your request. To find out where homebrew has installed curl execute:

I installed the latest ffmpeg and use the following:

/usr/local/bin/youtube-dl -q --no-warnings --fixup --prefer-ffmpeg -- ffmpeg-location /usr/local/bin -x "$1"

I get audio files consistently now (ogg, opus, m4a, etc). But errors still print on the screen. Good enough for now.

Just for info: the rtmpdump is apparently a requirement for some other OS... I compiled FFmpeg without rtmpdump/librtmp yesterday, and in the 'enabled protocols' at time of ./configure , I could see RTMP/RTMPS etc. as well...

Very surprised, I ran the compiled FFmpeg on the targetted ARM device, and it runs without any issue: I guess support was already there inside ffmpeg (for ARM), while I was wrestling with rtmpdump.