youtube auto generated subtitle not time synced with audio on mp4

[yunw3n]

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• 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
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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 ```):

# ---------- download the video at first time -----------------
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: [u'-v', u'-f', u'best[ext=mp4]/best', u'--write-auto-sub', u'--sub-lang', u'en', u'--embed-subs', u'--embed-thumbnail', u'IgSuFYamZas']
[debug] Encodings: locale UTF-8, fs utf-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2017.10.07
[debug] Python version 2.7.13 - Darwin-17.0.0-x86_64-i386-64bit
[debug] exe versions: ffmpeg 3.2.2, ffprobe 3.2.2
[debug] Proxy map: {'http': 'http://127.0.0.1:1087', 'https': 'http://127.0.0.1:1087'}
[youtube] IgSuFYamZas: Downloading webpage
[youtube] IgSuFYamZas: Downloading video info webpage
[youtube] IgSuFYamZas: Extracting video information
[youtube] IgSuFYamZas: Looking for automatic captions
[youtube] IgSuFYamZas: Downloading MPD manifest
[info] Writing video subtitles to: MIT 6.S191 Lecture 1 - Intro to Deep Learning-IgSuFYamZas.en.vtt
[youtube] IgSuFYamZas: Downloading thumbnail ...
[youtube] IgSuFYamZas: Writing thumbnail to: MIT 6.S191 Lecture 1 - Intro to Deep Learning-IgSuFYamZas.jpg
[debug] Invoking downloader on u'https://r6---sn-a5mlrn7d.googlevideo.com/videoplayback?signature=609DCE5736953E64B6A44DB63E4574C0A0E16AB4.417B54DA52F8C6B1E58FB3FA57027B80FB2F3FFE&expire=1507410218&ratebypass=yes&pl=23&mv=m&ei=yuzYWdmQJq2V_AP7_JvICA&ipbits=0&ms=au&mm=31&mime=video%2Fmp4&sparams=dur%2Cei%2Cid%2Cinitcwndbps%2Cip%2Cipbits%2Citag%2Clmt%2Cmime%2Cmm%2Cmn%2Cms%2Cmv%2Cpl%2Cratebypass%2Crequiressl%2Csource%2Cexpire&mn=sn-a5mlrn7d&key=yt6&source=youtube&dur=2096.390&mt=1507388520&id=o-ALn7t6MEsiBQZBjQXMMxgVrlvxGdf2k-IqAGo4n1WtgZ&lmt=1486021188926210&itag=22&requiressl=yes&ip=107.191.58.237&initcwndbps=9013750'
[download] Destination: MIT 6.S191 Lecture 1 - Intro to Deep Learning-IgSuFYamZas.mp4
[download] 100% of 100.07MiB in 03:43
[ffmpeg] Embedding subtitles in 'MIT 6.S191 Lecture 1 - Intro to Deep Learning-IgSuFYamZas.mp4'
[debug] ffmpeg command line: ffmpeg -y -i 'file:MIT 6.S191 Lecture 1 - Intro to Deep Learning-IgSuFYamZas.mp4' -i 'file:MIT 6.S191 Lecture 1 - Intro to Deep Learning-IgSuFYamZas.en.vtt' -map 0 -c copy -map '-0:s' '-c:s' mov_text -map '1:0' '-metadata:s:s:0' 'language=eng' 'file:MIT 6.S191 Lecture 1 - Intro to Deep Learning-IgSuFYamZas.temp.mp4'
Deleting original file MIT 6.S191 Lecture 1 - Intro to Deep Learning-IgSuFYamZas.en.vtt (pass -k to keep)
[atomicparsley] Adding thumbnail to "MIT 6.S191 Lecture 1 - Intro to Deep Learning-IgSuFYamZas.mp4"
[debug] AtomicParsley command line: AtomicParsley 'MIT 6.S191 Lecture 1 - Intro to Deep Learning-IgSuFYamZas.mp4' --artwork 'MIT 6.S191 Lecture 1 - Intro to Deep Learning-IgSuFYamZas.jpg' -o 'MIT 6.S191 Lecture 1 - Intro to Deep Learning-IgSuFYamZas.temp.mp4'

# ---------- play with mpv, subtitle not synced -----------------
mpv MIT\ 6.S191\ Lecture\ 1\ -\ Intro\ to\ Deep\ Learning-IgSuFYamZas.mp4

# ---------- So I download it again with youtube-dl ---------------------

[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: [u'-v', u'-f', u'best[ext=mp4]/best', u'--write-auto-sub', u'--sub-lang', u'en', u'--embed-subs', u'--embed-thumbnail', u'IgSuFYamZas']
[debug] Encodings: locale UTF-8, fs utf-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2017.10.07
[debug] Python version 2.7.13 - Darwin-17.0.0-x86_64-i386-64bit
[debug] exe versions: ffmpeg 3.2.2, ffprobe 3.2.2
[debug] Proxy map: {'http': 'http://127.0.0.1:1087', 'https': 'http://127.0.0.1:1087'}
[youtube] IgSuFYamZas: Downloading webpage
[youtube] IgSuFYamZas: Downloading video info webpage
[youtube] IgSuFYamZas: Extracting video information
[youtube] IgSuFYamZas: Looking for automatic captions
[youtube] IgSuFYamZas: Downloading MPD manifest
[info] Writing video subtitles to: MIT 6.S191 Lecture 1 - Intro to Deep Learning-IgSuFYamZas.en.vtt
[youtube] IgSuFYamZas: Downloading thumbnail ...
[youtube] IgSuFYamZas: Writing thumbnail to: MIT 6.S191 Lecture 1 - Intro to Deep Learning-IgSuFYamZas.jpg
[debug] Invoking downloader on u'https://r1---sn-a5mekn7y.googlevideo.com/videoplayback?mv=m&mt=1507388990&ms=au&id=o-AAQS_GbImsgX7nWQQvhZzyn6uoeWFgMbya5iP33nugn8&ei=ke7YWYa2Hor7-gPyiIeoDA&pl=23&source=youtube&expire=1507410673&dur=2096.390&ip=107.191.58.237&key=yt6&requiressl=yes&mn=sn-a5mekn7y&signature=AD183C60BE02D551DE4291D5FCEEFD22101C8617.3579F61EBADC2F7A97D41F2799713DC5CEC38F3C&sparams=dur%2Cei%2Cid%2Cinitcwndbps%2Cip%2Cipbits%2Citag%2Clmt%2Cmime%2Cmm%2Cmn%2Cms%2Cmv%2Cpl%2Cratebypass%2Crequiressl%2Csource%2Cexpire&ipbits=0&ratebypass=yes&itag=22&initcwndbps=9410000&mm=31&mime=video%2Fmp4&lmt=1486021188926210'
[download] MIT 6.S191 Lecture 1 - Intro to Deep Learning-IgSuFYamZas.mp4 has already been downloaded
[download] 100% of 101.32MiB
[ffmpeg] Embedding subtitles in 'MIT 6.S191 Lecture 1 - Intro to Deep Learning-IgSuFYamZas.mp4'
[debug] ffmpeg command line: ffmpeg -y -i 'file:MIT 6.S191 Lecture 1 - Intro to Deep Learning-IgSuFYamZas.mp4' -i 'file:MIT 6.S191 Lecture 1 - Intro to Deep Learning-IgSuFYamZas.en.vtt' -map 0 -c copy -map '-0:s' '-c:s' mov_text -map '1:0' '-metadata:s:s:0' 'language=eng' 'file:MIT 6.S191 Lecture 1 - Intro to Deep Learning-IgSuFYamZas.temp.mp4'
Deleting original file MIT 6.S191 Lecture 1 - Intro to Deep Learning-IgSuFYamZas.en.vtt (pass -k to keep)
[atomicparsley] Adding thumbnail to "MIT 6.S191 Lecture 1 - Intro to Deep Learning-IgSuFYamZas.mp4"
[debug] AtomicParsley command line: AtomicParsley 'MIT 6.S191 Lecture 1 - Intro to Deep Learning-IgSuFYamZas.mp4' --artwork 'MIT 6.S191 Lecture 1 - Intro to Deep Learning-IgSuFYamZas.jpg' -o 'MIT 6.S191 Lecture 1 - Intro to Deep Learning-IgSuFYamZas.temp.mp4'

# -------------- then, I play it with mpv and now the subtitle is synced, very weird ----------------------
mpv MIT\ 6.S191\ Lecture\ 1\ -\ Intro\ to\ Deep\ Learning-IgSuFYamZas.mp4

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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=IgSuFYamZas

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

Command:
youtube-dl -f 'best[ext=mp4]/best' --write-auto-sub --sub-lang en --embed-subs --embed-thumbnail IgSuFYamZas

After run this command, the video is downloaded successfully, but the subtitle embedded in video file which is automatic generated by Youtube is not time synced with audio. But, but, when I run the command again, it downloads the subtitle again, and skip the video download(video file exists), and embed the subtitle into video file again, and then the subtitle works well.

Really weird..guess there's some issue when merging subtitle file at first time.

Run the command below will reproduce the issue.

[dstftw]

You can compare final and intermediate files if you believe Youtube serves you different files.