Problem with embedding subtitles to mp4

[MrDemocracy]

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Make sure you are using the latest version: run youtube-dl --version and ensure your version is 2017.09.11. If it's not, read this FAQ entry and update. Issues with outdated version will be rejected.

• I've verified and I assure that I'm running youtube-dl 2017.09.11

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• Searched 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)
• Feature request (request for a new functionality)
• Question
• Other

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

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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 the -v flag to your command line you run youtube-dl with (youtube-dl -v <your command line>), 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 --all-subs --write-sub  --convert-subs srt  --embed-subs https://tv.nrk.no/serie/planeten-vaar/KOID26003216 --merge-output-format mkv -v
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: [u'--all-subs', u'--write-sub', u'--convert-subs', u'srt', u'--embed-subs', u'https://tv.nrk.no/serie/planeten-vaar/KOID26003216', u'--merge-output-format', u'mkv', u'-v']
[debug] Encodings: locale UTF-8, fs utf-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2017.09.11
[debug] Python version 2.7.13 - Darwin-16.7.0-x86_64-i386-64bit
[debug] exe versions: ffmpeg 3.3.2, ffprobe 3.3.2, rtmpdump 2.4
[debug] Proxy map: {}
[debug] Using fake IP 84.212.218.124 (NO) as X-Forwarded-For.
[NRKTV] KOID26003216: Downloading mediaelement JSON
[NRKTV] KOID26003216: Downloading f4m manifest
[NRKTV] KOID26003216: Downloading m3u8 information
[download] Downloading playlist: Planeten vår II 1:6
[NRKTV] playlist Planeten vår II 1:6: Collected 1 video ids (downloading 1 of them)
[download] Downloading video 1 of 1
[debug] Default format spec: bestvideo+bestaudio/best
[info] Writing video subtitles to: Planeten vår II 1_6-KOID26003216AA.no.ttml
[debug] Invoking downloader on u'http://nordond30c-f.akamaihd.net/i/no/open/1d/1d118ee6ada133dcc0aa19f03eb0f2b4f7d3c763/4e211d89-fb1d-4eee-b466-537826c1099f_,141,316,563,1266,2250,.mp4.csmil/index_4_av.m3u8?null=0'
[download] Planeten vår II 1_6-KOID26003216AA.mp4 has already been downloaded
[download] 100% of 872.68MiB
[debug] ffmpeg command line: ffprobe -show_streams 'file:Planeten vår II 1_6-KOID26003216AA.mp4'
[ffmpeg] Fixing malformed AAC bitstream in "Planeten vår II 1_6-KOID26003216AA.mp4"
[debug] ffmpeg command line: ffmpeg -y -i 'file:Planeten vår II 1_6-KOID26003216AA.mp4' -c copy -f mp4 '-bsf:a' aac_adtstoasc 'file:Planeten vår II 1_6-KOID26003216AA.temp.mp4'
[ffmpeg] Converting subtitles
WARNING: You have requested to convert dfxp (TTML) subtitles into another format, which results in style information loss
Deleting original file Planeten vår II 1_6-KOID26003216AA.no.ttml (pass -k to keep)
[ffmpeg] Embedding subtitles in 'Planeten vår II 1_6-KOID26003216AA.mp4'
[debug] ffmpeg command line: ffmpeg -y -i 'file:Planeten vår II 1_6-KOID26003216AA.mp4' -i 'file:Planeten vår II 1_6-KOID26003216AA.no.srt' -map 0 -c copy -map '-0:s' '-c:s' mov_text -map '1:0' '-metadata:s:s:0' 'language=nor' 'file:Planeten vår II 1_6-KOID26003216AA.temp.mp4'
Deleting original file Planeten vår II 1_6-KOID26003216AA.no.srt (pass -k to keep)
[download] Finished downloading playlist: Planeten vår II 1:6

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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):

(happens for all videos downloaded)

Note that youtube-dl does not support sites dedicated to copyright infringement. In order for site support request to be accepted all provided example URLs should not violate any copyrights.

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Description of your issue, suggested solution and other information

I would like it to output a mkv file, and have a properly embedded subtitle. The subtitle can not be seen when I open the file with MKVToolNix Gui, but does however show up in VLC.
The subtitle is nearly microscopic in VLC, and can not be resized by changing the settings in the VLC dropdown menu.

--recode-video video takes forever to finish (with no progress status/information), and --merge-output-format does nothing.