Dash video won't be merged properly (wrong duration)

[fireattack]

Checklist

• I'm reporting a broken site support issue
• I've verified that I'm running youtube-dl version 2020.01.15
• I've checked that all provided URLs are alive and playable in a browser
• I've checked that all URLs and arguments with special characters are properly quoted or escaped
• I've searched the bugtracker for similar bug reports including closed ones
• I've read bugs section in FAQ

Verbose log

(See below)

Description

When downloading Dash video from YouTube, the downloaded/merged video and audio file will have wrong timecodes (duration), and therefore can't be played properly.

Since Dash video only exists shortly after a live stream is ended (and later will be replaced by other formats), it is hard to give you an example log right now.

But below is the JSON log for such a video I downloaded before using youtube-dl https://www.youtube.com/watch?v=slfkswYSf8Y -f 136+140 -k.

20191223 アイドルマスター家庭用最新作制作発表会!!-youtube-slfkswYSf8Y.info.json.txt

The downloaded f136.mp4 (video), f140.m4a (audio), and merged mp4 can't be played properly and reports duration of only 9 seconds.

[fireattack]

Would you mind to kindly let me know which issue this is duplicated to? I tried to search with "dash" and "duration" before I posted, but didn't find anything similar.