Repository: youtube-dl
Issue: Multiple connection support in internal dash downloader
Labels: request

## Please follow the guide below
- 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 _2016.10.26_. 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 Issues with outdated version will be rejected.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 **2016.10.26**
### 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_?
- [ ] Bug report (encountered problems with youtube-dl)
- [ ] Site support request (request for adding support for a new site)
- [x] 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 ```):

```
C:\Video>youtube-dl --external-downloader axel http://genflix.orangetv.asia.swiftserve.com/US/videoContent-1530-iqn62l7c-v1/videoContent-1530-iqn62l7c-m1-4-NoneUS/1487-1530-m1-iqn62l7c-default.ism/a.mpd -v
[debug] System config: []
[debug] User config: []
[debug] Command-line args: ['--external-downloader', 'axel', 'http://genflix.orangetv.asia.swiftserve.com/US/videoContent-1530-iqn62l7c-v1/videoContent-1530-iqn62l7c-m1-4-NoneUS/1487-1530-m1-iqn62l7c-default.ism/a.mpd', '-v']
[debug] Encodings: locale cp1252, fs mbcs, out cp437, pref cp1252
[debug] youtube-dl version 2016.10.26
[debug] Python version 3.4.4 - Windows-10-10.0.10240
[debug] exe versions: ffmpeg N-82117-gc117343, ffprobe N-82117-gc117343, rtmpdump 2.3
[debug] Proxy map: {}
[generic] a: Requesting header
WARNING: Falling back on generic information extractor.
[generic] a: Downloading webpage
[generic] a: Extracting information
[debug] Invoking downloader on 'http://genflix.orangetv.asia.swiftserve.com/US/videoContent-1530-iqn62l7c-v1/videoContent-1530-iqn62l7c-m1-4-NoneUS/1487-1530-m1-iqn62l7c-default.ism/dash/'
[dashsegments] Total fragments: 3222
```

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### If the purpose of this _issue_ is a _site support request_ please provide all kinds of example URLs support for which should be included (replace following example URLs by **yours**):
- Single video: https://www.youtube.com/watch?v=BaW_jenozKc
- Single video: https://youtu.be/BaW_jenozKc
- Playlist: https://www.youtube.com/playlist?list=PL4lCao7KL_QFVb7Iudeipvc2BCavECqzc

https://bitdash-a.akamaihd.net/content/sintel/sintel.mpd
http://genflix.orangetv.asia.swiftserve.com/US/videoContent-1633-istumdrs-v1/videoContent-1633-istumdrs-m1-4-NoneUS/1584-1633-m1-istumdrs-default.ism/a.mpd

---
### Description of your _issue_, suggested solution and other information

Explanation of your _issue_ in arbitrary form goes here. Please make sure the [description is worded well enough to be understood](https://github.com/rg3/youtube-dl#is-the-description-of-the-issue-itself-sufficient). Provide as much context and examples as possible.
If work on your _issue_ requires account credentials please provide them or explain how one can obtain them.

Please add support for multiple connection / thread when downloading mpd video stream as sometime using youtube-dl to download it can be slow even when you have high internet speed, example when downloading from the second example above i mostly only get 20 - 200 KB/sec

as youtube-dl seem to ignore the --external-downloader when downloading mpd file