Repository: youtube-dl
Issue: Youtube-dl can't merge VP9+Opus youtube videos
Labels: duplicate

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## Checklist

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Carefully read and work through this check list in order to prevent the most common mistakes and misuse of youtube-dl:
- First of, make sure you are using the latest version of youtube-dl. Run `youtube-dl --version` and ensure your version is 2021.01.24.1. If it's not, see https://yt-dl.org/update on how to update. Issues with outdated version will be REJECTED.
- Make sure that all provided video/audio/playlist URLs (if any) are alive and playable in a browser.
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- [x] I'm reporting a broken site support
- [x] I've verified that I'm running youtube-dl version **2021.01.24.1**
- [x] I've checked that all provided URLs are alive and playable in a browser
- [x] I've checked that all URLs and arguments with special characters are properly quoted or escaped
- [x] I've searched the bugtracker for similar issues including closed ones


## Verbose log

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Provide the complete verbose output of youtube-dl that clearly demonstrates the problem.
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 below. It should look similar to this:
 [debug] System config: []
 [debug] User config: []
 [debug] Command-line args: [u'-v', u'http://www.youtube.com/watch?v=BaW_jenozKcj']
 [debug] Encodings: locale cp1251, fs mbcs, out cp866, pref cp1251
 [debug] youtube-dl version 2021.01.24.1
 [debug] Python version 2.7.11 - Windows-2003Server-5.2.3790-SP2
 [debug] exe versions: ffmpeg N-75573-g1d0487f, ffprobe N-75573-g1d0487f, rtmpdump 2.4
 [debug] Proxy map: {}
 <more lines>
-->

```
youtube-dl -v --abort-on-unavailable-fragment -f (bestvideo[vcodec=vp9])+(bestaudio[acodec=opus]) https://youtu.be/g6zva0stnOY --no-continue

[debug] System config: []                                                          
[debug] User config: []                                                            
[debug] Custom config: []                                                          
[debug] Command-line args: ['-v', '--abort-on-unavailable-fragment', '-f', '(bestvideo[vcodec=vp9])+(bestaudio[acodec=opus])', 'https://youtu.be/g6zva0stnOY', '--no-continue']   
                                                                       
[debug] Encodings: locale UTF-8, fs utf-8, out utf-8, pref UTF-8  
                 
[debug] youtube-dl version 2021.01.24.1          
                                  
[debug] Python version 3.8.7 (CPython) - Linux-5.10.11-0-lts-x86_64-with           

[debug] exe versions: ffmpeg 4.3.1, ffprobe 4.3.1                                  

[debug] Proxy map: {}                                                              
[youtube] g6zva0stnOY: Downloading webpage                                         
[youtube] g6zva0stnOY: Downloading MPD manifest                                    
[debug] Invoking downloader on [REDACTED]

[dashsegments] Total fragments: 280                                                
[download] Destination: المحاضرة الثانية _ الثرموداينمك _ الجزء الثاني 2021-g6zva0stnOY.f302.webm                                                                     
[download] 100% of 417.83MiB in 24:16                                              
[debug] Invoking downloader on [REDACTED]
[dashsegments] Total fragments: 157
[download] Destination: المحاضرة الثانية _ الثرموداينمك _ الجزء الثاني 2021-g6zva0stnOY.f251.webm
[download] 100% of 22.60MiB in 00:36
[ffmpeg] Merging formats into "المحاضرة الثانية _ الثرموداينمك _ الجزء الثاني 2021-g6zva0stnOY.webm"
[debug] ffmpeg command line: ffmpeg -y -loglevel repeat+info -i 'file:المحاضرة الثانية _ الثرموداينمك _ الجزء الثاني 2021-g6zva0stnOY.f302.webm' -i 'file:المحاضرة الثانية _ الثرموداينمك _ الجزء الثاني 2021-g6zva0stnOY.f251.webm' -c copy -map 0:v:0 -map 1:a:0 'file:المحاضرة الثانية _ الثرموداينمك _ الجزء الثاني 2021-g6zva0stnOY.temp.webm'
ERROR: Conversion failed!
Traceback (most recent call last):
  File "/usr/lib/python3.8/site-packages/youtube_dl/YoutubeDL.py", line 2102, in post_process
    files_to_delete, info = pp.run(info)
  File "/usr/lib/python3.8/site-packages/youtube_dl/postprocessor/ffmpeg.py", line 523, in run
    self.run_ffmpeg_multiple_files(info['__files_to_merge'], temp_filename, args)
  File "/usr/lib/python3.8/site-packages/youtube_dl/postprocessor/ffmpeg.py", line 235, in run_ffmpeg_multiple_files
    raise FFmpegPostProcessorError(msg)
youtube_dl.postprocessor.ffmpeg.FFmpegPostProcessorError: Conversion failed!
```


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FFmpeg gives me the following error when I run   the command mentioned in the above output manually:

`[webm @ 0x7fe94ccf40c0] Application provided invalid, non monotonically increasing dts to muxer in stream 0: 5620 >= 5600
av_interleaved_write_frame(): Invalid argument`

I've tried to re-download it multiple times and the issue persists. Other videos can be merged fine, so it seems like this is a problem with this particular video.