youtube-dl replaces aria2 with ffmpeg as external downloader. Inform user?

[0x41mmarVM]

Duplicate of #10784

Checklist

• [ X ] I'm asking a question
• [ X ] I've looked through the README and FAQ for similar questions
• [ X ] I've searched the bugtracker for similar questions including closed ones

Question

When calling youtube-dl on a segmented HLS/DASH and specifying an external downloader (aria2c), it silently switches to ffmpeg, and passes it the --external-downloader-args intended for aria2. This has been referred to in this issue, which was closed as duplicate, but I couldn't find what it was a duplicate of, nor did the author.
After searching issues for a while I now understand that aria2 does not support HLS or Segmented DASH, but shouldn't ytdl inform somehow before silently switching to ffmpeg?

Verbose Log:
`

youtube-dl -v --external-downloader aria2c --external-downloader-args "-hide_banner -x 10" https://devstreaming-cdn.apple.com/videos/streaming/examples/bipbop_16x9/bipbop_16x9_variant.m3u8
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['-v', '--external-downloader', 'aria2c', '--external-downloader-args', '-hide_banner -x 10', 'https://devstreaming-cdn.apple.com/videos/streaming/examples/bipbop_16x9/bipbop_16x9_variant.m3u8']
[debug] Encodings: locale cp1252, fs mbcs, out cp850, pref cp1252
[debug] youtube-dl version 2019.07.30
[debug] Python version 3.4.4 (CPython) - Windows-10-10.0.17763
[debug] exe versions: avconv 9.18, avprobe 9.18, ffmpeg 4.1.1, ffprobe N-93894-gecc096513c, phantomjs 2.1.1
[debug] Proxy map: {}
[generic] bipbop_16x9_variant: Requesting header
[generic] bipbop_16x9_variant: Downloading m3u8 information
[debug] Default format spec: bestvideo+bestaudio/best
[debug] Invoking downloader on 'https://devstreaming-cdn.apple.com/videos/streaming/examples/bipbop_16x9/gear5/prog_index.m3u8'
[download] Destination: bipbop_16x9_variant-bipbop_16x9_variant.mp4
[debug] ffmpeg command line: ffmpeg -y -loglevel verbose -hide_banner -x 10 -headers "Accept-Charset: ISO-8859-1,utf-8;q=0.7,;q=0.7
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.114 Safari/537.36
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip, deflate
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,/*;q=0.8
" -i "https://devstreaming-cdn.apple.com/videos/streaming/examples/bipbop_16x9/gear5/prog_index.m3u8" -c copy -f mp4 "file:bipbop_16x9_variant-bipbop_16x9_variant.mp4.part"
Unrecognized option 'x'.
Error splitting the argument list: Option not found

ERROR: ffmpeg exited with code 1

`

[0x41mmarVM]

The question is simply: If this is intended behaviour, should there not be some message?
If there is more nuance to it, I've really really tried to find the issue this is a duplicate of.

[shadowzoom]

@ 0x41mmarVM do you find a way to download multithreads this hls m3u8 file?

[cgorlla]

So, is anything planned for this? I'm still experiencing this issue. Aria2 will hand something off to ffmpeg then ffmpeg tries to parse the -ext-dl-args meant for Aria.

[0x41mmarVM]

@shadowzoom No, no solution found. That said, I wasn’t looking for a solution, I just wanted a message in the log telling me that ffmpeg was subbed in, so that I don’t spend an hour messing with command switches and trying to understand why aria2c doesn’t understand my request. The silent switching was a bit mean.

[maxnordlund]

I think I found the duplicate, #10784, but only @dstftw can confirm that one is it?

[0x41mmarVM]

I think I found the duplicate, #10784, but only @dstftw can confirm that one is it?

Oh hey, that looks right. Sad it’s still open.
I’ve added it in the description so people find it easier.