Repository: youtube-dl
Issue: --external-downloader-args should be ignored when --external-downloader isn't used
Labels: bug

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- You will be asked some questions and requested to provide some information, please read them **carefully** and answer honestly
- Put an `x` into all the boxes [ ] relevant to your _issue_ (like that [x])
- Use _Preview_ tab to see how your issue will actually look like

---
### Make sure you are using the _latest_ version: run `youtube-dl --version` and ensure your version is _2016.09.27_. If it's not read [this FAQ entry](https://github.com/rg3/youtube-dl/blob/master/README.md#how-do-i-update-youtube-dl) and update. Issues with outdated version will be rejected.
- [x] I've **verified** and **I assure** that I'm running youtube-dl **2016.09.27**
### Before submitting an _issue_ make sure you have:
- [x] At least skimmed through [README](https://github.com/rg3/youtube-dl/blob/master/README.md) and **most notably** [FAQ](https://github.com/rg3/youtube-dl#faq) and [BUGS](https://github.com/rg3/youtube-dl#bugs) sections
- [x] [Searched](https://github.com/rg3/youtube-dl/search?type=Issues) the bugtracker for similar issues including closed ones
### What is the purpose of your _issue_?
- [x] Bug report (encountered problems with youtube-dl)
- [ ] Site support request (request for adding support for a new site)
- [ ] Feature request (request for a new functionality)
- [ ] Question
- [ ] Other

---
### The following sections concretize particular purposed issues, you can erase any section (the contents between triple ---) not applicable to your _issue_

---
### If the purpose of this _issue_ is a _bug report_, _site support request_ or you are not completely sure provide the full verbose output as follows:

Add `-v` flag to **your command line** you run youtube-dl with, copy the **whole** output and insert it here. It should look similar to one below (replace it with **your** log inserted between triple ```):

```
$ youtube-dl -v https://twitter.com/CrazyByAnittaOf/status/780841028303646720
[debug] System config: []
[debug] User config: ['--external-downloader=aria2c', '--external-downloader-args=--file-allocation=falloc --max-connection-per-server=10 --min-split-size=1M', '--netrc', '--ignore-errors', '--prefer-ffmpeg']
[debug] Command-line args: ['-v', 'https://twitter.com/CrazyByAnittaOf/status/780841028303646720']
[debug] Encodings: locale UTF-8, fs utf-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2016.09.27
[debug] Python version 3.5.1 - Darwin-16.0.0-x86_64-i386-64bit
[debug] exe versions: avconv 11.4, avprobe 11.4, ffmpeg 3.1.2, ffprobe 3.1.2, rtmpdump 2.4
[debug] Proxy map: {}
[twitter] 780841028303646720: Downloading webpage
[twitter:card] 780841028303646720: Downloading webpage
[twitter:card] 780841028303646720: Downloading m3u8 information
[debug] Invoking downloader on 'https://video.twimg.com/ext_tw_video/780840843628380161/pu/pl/480x480/1ne3LEaCrDHpwPvG.m3u8'
[download] Destination: Crazy By Anitta - MINHA amoree #MPN #anitta-780841028303646720.mp4
[debug] ffmpeg command line: ffmpeg -y --file-allocation=falloc --max-connection-per-server=10 --min-split-size=1M -headers 'Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Accept-Language: en-us,en;q=0.5
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0) Gecko/20150101 Firefox/47.0 (Chrome)
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Encoding: gzip, deflate
' -i https://video.twimg.com/ext_tw_video/780840843628380161/pu/pl/480x480/1ne3LEaCrDHpwPvG.m3u8 -c copy -f mp4 -bsf:a aac_adtstoasc 'file:Crazy By Anitta - MINHA amoree #MPN #anitta-780841028303646720.mp4.part'
ffmpeg version 3.1.2 Copyright (c) 2000-2016 the FFmpeg developers
  built with Apple LLVM version 7.3.0 (clang-703.0.31)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/3.1.2 --enable-shared --enable-pthreads --enable-gpl --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-opencl --enable-libx264 --enable-libmp3lame --enable-libxvid --enable-libfreetype --enable-libtheora --enable-libvorbis --enable-libvpx --enable-librtmp --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libfaac --enable-libass --enable-ffplay --enable-libspeex --enable-libschroedinger --enable-libfdk-aac --enable-libopus --enable-frei0r --enable-libx265 --disable-lzma --enable-libopenjpeg --disable-decoder=jpeg2000 --extra-cflags= --enable-nonfree --enable-vda
  libavutil      55. 28.100 / 55. 28.100
  libavcodec     57. 48.101 / 57. 48.101
  libavformat    57. 41.100 / 57. 41.100
  libavdevice    57.  0.101 / 57.  0.101
  libavfilter     6. 47.100 /  6. 47.100
  libavresample   3.  0.  0 /  3.  0.  0
  libswscale      4.  1.100 /  4.  1.100
  libswresample   2.  1.100 /  2.  1.100
  libpostproc    54.  0.100 / 54.  0.100
Unrecognized option '-file-allocation=falloc'.
Error splitting the argument list: Option not found


ERROR: ffmpeg exited with code 1
  File "/Users/silvior/anaconda/lib/python3.5/runpy.py", line 170, in _run_module_as_main
    "__main__", mod_spec)
  File "/Users/silvior/anaconda/lib/python3.5/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/usr/local/bin/youtube-dl/__main__.py", line 19, in <module>
    youtube_dl.main()
  File "/usr/local/bin/youtube-dl/youtube_dl/__init__.py", line 449, in main
    _real_main(argv)
  File "/usr/local/bin/youtube-dl/youtube_dl/__init__.py", line 439, in _real_main
    retcode = ydl.download(all_urls)
  File "/usr/local/bin/youtube-dl/youtube_dl/YoutubeDL.py", line 1791, in download
    url, force_generic_extractor=self.params.get('force_generic_extractor', False))
  File "/usr/local/bin/youtube-dl/youtube_dl/YoutubeDL.py", line 705, in extract_info
    return self.process_ie_result(ie_result, download, extra_info)
  File "/usr/local/bin/youtube-dl/youtube_dl/YoutubeDL.py", line 776, in process_ie_result
    new_result, download=download, extra_info=extra_info)
  File "/usr/local/bin/youtube-dl/youtube_dl/YoutubeDL.py", line 751, in process_ie_result
    return self.process_video_result(ie_result, download=download)
  File "/usr/local/bin/youtube-dl/youtube_dl/YoutubeDL.py", line 1435, in process_video_result
    self.process_info(new_info)
  File "/usr/local/bin/youtube-dl/youtube_dl/YoutubeDL.py", line 1699, in process_info
    success = dl(filename, info_dict)
  File "/usr/local/bin/youtube-dl/youtube_dl/YoutubeDL.py", line 1641, in dl
    return fd.download(name, info)
  File "/usr/local/bin/youtube-dl/youtube_dl/downloader/common.py", line 354, in download
    return self.real_download(filename, info_dict)
  File "/usr/local/bin/youtube-dl/youtube_dl/downloader/external.py", line 43, in real_download
    self.get_basename(), retval))
  File "/usr/local/bin/youtube-dl/youtube_dl/downloader/common.py", line 162, in report_error
    self.ydl.report_error(*args, **kargs)
  File "/usr/local/bin/youtube-dl/youtube_dl/YoutubeDL.py", line 568, in report_error
    self.trouble(error_message, tb)
  File "/usr/local/bin/youtube-dl/youtube_dl/YoutubeDL.py", line 530, in trouble
    tb_data = traceback.format_list(traceback.extract_stack())
```
### Description of your _issue_, suggested solution and other information

When I tried to download a video from twitter, youtube-dl used the args passed to aria2c from ~/.config/youtube-dl/config to ffmpeg causing the above error.