It doesn't skip through already downloaded videos

[sandygliese]

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Make sure you are using the latest version: run youtube-dl --version and ensure your version is 2018.12.17. 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 Issues with outdated version will be rejected.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 2018.12.17

Before submitting an issue make sure you have:

• At least skimmed through the README, most notably the FAQ and BUGS sections
• Searched the bugtracker for similar issues including closed ones
• Checked that provided video/audio/playlist URLs (if any) are alive and playable in a browser

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

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:

[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['-v', '-o', '%(title)s-%(upload_date)s.%(ext)s', 'https://www.youtube.com/playlist?list=PLH15HpR5qRsUtTv7IQKftKGOcRLGtwuoF']
[debug] Encodings: locale cp1252, fs mbcs, out cp437, pref cp1252
[debug] youtube-dl version 2018.12.17
[debug] Python version 3.4.4 (CPython) - Windows-10-10.0.17763
[debug] exe versions: ffmpeg 2.2.2
[debug] Proxy map: {}
[youtube:playlist] PLH15HpR5qRsUtTv7IQKftKGOcRLGtwuoF: Downloading webpage
[download] Downloading playlist: Black Hat USA 2013
[youtube:playlist] PLH15HpR5qRsUtTv7IQKftKGOcRLGtwuoF: Downloading page #1
[youtube:playlist] playlist Black Hat USA 2013: Downloading 102 videos
[download] Downloading video 1 of 102
[youtube] b9uGcxDhrzw: Downloading webpage
[youtube] b9uGcxDhrzw: Downloading video info webpage
[debug] Default format spec: bestvideo+bestaudio/best
WARNING: Requested formats are incompatible for merge and will be merged into mkv.
[debug] Invoking downloader on 'https://r4---sn-nv4uj5aa-cvhe.googlevideo.com/videoplayback?lmt=1386178335533371&source=youtube&dur=492.867&aitags=133%2C134%2C135%2C136%2C160%2C242%2C243%2C244%2C247%2C278&requiressl=yes&gir=yes&key=yt6&signature=2704310D7DE6E751F725BA43E71E92B773B2FF58.1A7AECCB74EFE8E4BD9F4072E0967D662BEFBC71&itag=136&expire=1546124796&fvip=4&ei=nKknXOSWIJGr8QOcs6DgBQ&ms=au%2Crdu&mt=1546103092&mv=m&pl=24&ip=139.5.44.102&keepalive=yes&id=o-ABFHzKx-63VTXihHHnKDh-iOTqf9B6ewhgA-ldnGZ0-R&mm=31%2C29&mn=sn-nv4uj5aa-cvhe%2Csn-cvh7kney&clen=73022269&sparams=aitags%2Cclen%2Cdur%2Cei%2Cgir%2Cid%2Cinitcwndbps%2Cip%2Cipbits%2Citag%2Ckeepalive%2Clmt%2Cmime%2Cmm%2Cmn%2Cms%2Cmv%2Cpl%2Crequiressl%2Csource%2Cexpire&initcwndbps=711250&mime=video%2Fmp4&ipbits=0&c=WEB&ratebypass=yes'
[download] Destination: Black Hat USA 2013 - A Tribute to Barnaby Jack-20131204.f136.mp4
<end of log>

Few context setting

I encounter this error when I try to download entire playlists.

The main reason I am even reporting this as a issue, is because I wasn't facing it using an older version (2016.6.27.0)
I tried executing the older one, but it wasn't able to download any video and suggested me to update the program to latest version instead (2018.12.17)

So, I don't know if this is a bug or conflict with updated features, but the problem in nutshell is ..

The program is re-downloading already downloaded videos.. in a weird way (explanation below).

Description of your issue, suggested solution and other information

Let's say I have already downloaded a video named A.mp4 from the playlist, which is the best format out of all available formats.
1. If I run the program again, it re-downloads 2 files named A.f136.mp4 & A.f251.webm and then merges them together to form a A.mkv file.
2. If there already exists a file name A.f136.mp4 it skips that and rest of Step (1) is repeated.

I am able to workaround this issue if I explicitly specify the best format while downloading the playlist. Verbose log for the same is specified below

[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['-v', '-f', '22', '-o', '%(title)s-%(upload_date)s.%(ext)s', 'https://www.youtube.com/playlist?list=PLH15HpR5qRsUtTv7IQKftKGOcRLGtwuoF']
[debug] Encodings: locale cp1252, fs mbcs, out cp437, pref cp1252
[debug] youtube-dl version 2018.12.17
[debug] Python version 3.4.4 (CPython) - Windows-10-10.0.17763
[debug] exe versions: ffmpeg 2.2.2
[debug] Proxy map: {}
[youtube:playlist] PLH15HpR5qRsUtTv7IQKftKGOcRLGtwuoF: Downloading webpage
[download] Downloading playlist: Black Hat USA 2013
[youtube:playlist] PLH15HpR5qRsUtTv7IQKftKGOcRLGtwuoF: Downloading page #1
[youtube:playlist] playlist Black Hat USA 2013: Downloading 102 videos
[download] Downloading video 1 of 102
[youtube] b9uGcxDhrzw: Downloading webpage
[youtube] b9uGcxDhrzw: Downloading video info webpage
[debug] Invoking downloader on 'https://r4---sn-nv4uj5aa-cvhe.googlevideo.com/videoplayback?mime=video%2Fmp4&ip=139.5.44.102&itag=22&mm=31%2C29&mn=sn-nv4uj5aa-cvhe%2Csn-cvh76nes&key=yt6&mt=1546104239&initcwndbps=703750&mv=m&id=o-AOjxKPLrv3O9J0IgaD0ngQvk6EZfs_ncYmA0GqTfpAOD&ms=au%2Crdu&signature=513D59BD56BB901556EB31B38BFBE37AC3394F5E.18708DF32D723396872143853C7B9AAFDD7153DF&fvip=4&expire=1546126011&sparams=dur%2Cei%2Cid%2Cinitcwndbps%2Cip%2Cipbits%2Citag%2Clmt%2Cmime%2Cmm%2Cmn%2Cms%2Cmv%2Cpl%2Cratebypass%2Crequiressl%2Csource%2Cexpire&ei=W64nXKjkF8SRmgeT5KC4Aw&c=WEB&lmt=1470917443654903&pl=24&requiressl=yes&ratebypass=yes&source=youtube&dur=492.982&ipbits=0'
[download] Black Hat USA 2013 - A Tribute to Barnaby Jack-20131204.mp4 has already been downloaded

[dstftw]

Formats may change on youtube side so that bestvideo and bestaudio from the past are no longer best. In that case completely different formats may be downloaded with different codecs producing different files.
Use --download-archive to track already downloaded files by video id.