To improve the download possibilities with youtube-dl it would be good to have ffmpeg. I thought it would be possible to install this application as I managed to do it for youtube-dl. So I use in StaSh the command: pip install ffmpeg. But after a trial, I got warning messages:

StaSh v0.7.2 on python 2.7.12
Tip: You can redirect output to Pythonista console, e.g. ls > &3
[~/Documents]$ youtube-dl -f 140 --add-metadata -o 'Petite fleur (Album Studio - Infos Wikipédia - AAC 128k).%(ext)s' https://youtu.be/vdoT29UbYig
[youtube] vdoT29UbYig: Downloading webpage
[youtube] vdoT29UbYig: Downloading video info webpage
[download] Destination: Petite fleur (Album Studio - Infos Wikipdia - AAC 128k).m4a
[download] 100% of 3.04MiB in 00:02
WARNING: vdoT29UbYig: writing DASH m4a. Only some players support this container. Install ffmpeg or avconv to fix this automatically.
[ffmpeg] Adding metadata to 'Petite fleur (Album Studio - Infos Wikipdia - AAC 128k).m4a'
ERROR: ffmpeg or avconv not found. Please install one.
[~/Documents]$

And if I try to reinstall ffmpeg I get another message:

[~/Documents]$ pip install ffmpeg
Error: Package already installed

What can I do to solve this problem ?

Hi,
I am a poor retired french man whose old Mac Mini of 10 years has just broken down. I try to reconstruct on an iPad Mini 2 (iOS 12) the audio-video environment that occupied my days on my Mac. I discovered by chance that one could use youtube-dl on an iPad thanks to Pythonista and I'm very pleased to use now Pythonista;-) Now I would like to find a way to attach an image to a file audio only (codec Opus, container webm), as I did with MKVToolNix on Mac.