[Youtube] Fetching some videos results in desynced audio

[goldirocks]

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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 ```):

[debug] System config: []
[debug] User config: [u'--prefer-ffmpeg']
[debug] Custom config: []
[debug] Command-line args: [u'-v', u'https://www.youtube.com/watch?v=co19vWFJZ90']
[debug] Encodings: locale UTF-8, fs UTF-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2017.09.15
[debug] Python version 2.7.13 - Linux-4.9.0-3-amd64-x86_64-with-debian-9.1
[debug] exe versions: ffmpeg 3.2.7-1, ffprobe 3.2.7-1, rtmpdump 2.4
[debug] Proxy map: {}
[youtube] co19vWFJZ90: Downloading webpage
[youtube] co19vWFJZ90: Downloading video info webpage
[youtube] co19vWFJZ90: Extracting video information
[youtube] co19vWFJZ90: Downloading MPD manifest
[debug] Default format spec: bestvideo+bestaudio/best
[debug] Invoking downloader on u'https://r6---sn-8xgp1vo-xfg6.googlevideo.com/videoplayback?id=728d7dbd614967dd&itag=137&source=youtube&requiressl=yes&initcwndbps=1233750&mm=31&mn=sn-8xgp1vo-xfg6&pl=24&ms=au&mv=m&ei=5I7EWfjXHI2U8gTzrJGACg&ratebypass=yes&mime=video/mp4&gir=yes&clen=128008691&lmt=1384735430684491&dur=514.381&key=dg_yt0&beids=[9466593]&mt=1506053737&signature=0331876FD3DAE996196BCF0285FAC10E0E7EDF3C.7D86E5E29BE70A8A221DBFFC729A086DBBDB8345&ip=98.116.146.216&ipbits=0&expire=1506075460&sparams=ip,ipbits,expire,id,itag,source,requiressl,initcwndbps,mm,mn,pl,ms,mv,ei,ratebypass,mime,gir,clen,lmt,dur'
[download] Destination: Self Massage Techniques for Face, Headaches, Neck Pain, TMJ, Relaxing How to _ Austin Chair Massage-co19vWFJZ90.f137.mp4
[download] 100% of 122.08MiB in 00:07
[debug] Invoking downloader on u'https://r6---sn-8xgp1vo-xfg6.googlevideo.com/videoplayback?id=728d7dbd614967dd&itag=140&source=youtube&requiressl=yes&initcwndbps=1233750&mm=31&mn=sn-8xgp1vo-xfg6&pl=24&ms=au&mv=m&ei=5I7EWfjXHI2U8gTzrJGACg&ratebypass=yes&mime=audio/mp4&gir=yes&clen=8308204&lmt=1403557097854057&dur=517.479&key=dg_yt0&beids=[9466593]&mt=1506053737&signature=4B5B6F12495E25455A17F412E37441F886BFEDC7.83FB5269D5EAB8B5C0964FCF03B4000A73DD5B32&ip=98.116.146.216&ipbits=0&expire=1506075460&sparams=ip,ipbits,expire,id,itag,source,requiressl,initcwndbps,mm,mn,pl,ms,mv,ei,ratebypass,mime,gir,clen,lmt,dur'
[download] Destination: Self Massage Techniques for Face, Headaches, Neck Pain, TMJ, Relaxing How to _ Austin Chair Massage-co19vWFJZ90.f140.m4a
[download] 100% of 7.92MiB in 00:00
[ffmpeg] Merging formats into "Self Massage Techniques for Face, Headaches, Neck Pain, TMJ, Relaxing How to _ Austin Chair Massage-co19vWFJZ90.mp4"
[debug] ffmpeg command line: ffmpeg -y -i 'file:Self Massage Techniques for Face, Headaches, Neck Pain, TMJ, Relaxing How to _ Austin Chair Massage-co19vWFJZ90.f137.mp4' -i 'file:Self Massage Techniques for Face, Headaches, Neck Pain, TMJ, Relaxing How to _ Austin Chair Massage-co19vWFJZ90.f140.m4a' -c copy -map '0:v:0' -map '1:a:0' 'file:Self Massage Techniques for Face, Headaches, Neck Pain, TMJ, Relaxing How to _ Austin Chair Massage-co19vWFJZ90.temp.mp4'
Deleting original file Self Massage Techniques for Face, Headaches, Neck Pain, TMJ, Relaxing How to _ Austin Chair Massage-co19vWFJZ90.f137.mp4 (pass -k to keep)
Deleting original file Self Massage Techniques for Face, Headaches, Neck Pain, TMJ, Relaxing How to _ Austin Chair Massage-co19vWFJZ90.f140.m4a (pass -k to keep)

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Description of your issue, suggested solution and other information

When fetching some videos (the example above is https://www.youtube.com/watch?v=co19vWFJZ90), the resulting output file has audio several seconds behind the video.

It seems like what occurred, comparing the output file to the playback in-browser, is that the video includes a several-second opening at the front of the video which is reproduced in the audio youtube-dl fetched but not in the video stream, resulting in the desync.

(I tried removing --prefer-ffmpeg and confirmed the issue remains, just in case.)