youtube-dl --verbose --merge-output-format mp4  https://www.youtube.com/watch?v=AeUPQa5H8BI
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['--verbose', '--merge-output-format', 'mp4', 'https://www.youtube.com/watch?v=AeUPQa5H8BI']
[debug] Encodings: locale cp1252, fs mbcs, out cp437, pref cp1252
[debug] youtube-dl version 2020.03.08
[debug] Python version 3.4.4 (CPython) - Windows-10-10.0.18362
[debug] exe versions: ffmpeg 4.2.2, ffprobe 4.2.2
[debug] Proxy map: {}
[youtube] AeUPQa5H8BI: Downloading webpage
[debug] Default format spec: bestvideo+bestaudio/best
[debug] Invoking downloader on 'https://r1---sn-n4v7sn7z.googlevideo.com/videoplayback?expire=1585291042&ei=wkp9XvbnB47TkgaF14TQDg&ip=98.176.94.192&id=o-AJNzsLN2X_qYEkviNJRUwP70l6GenJE6yV_QPjNMRBbz&itag=137&aitags=133%2C134%2C135%2C136%2C137%2C160%2C242%2C243%2C244%2C247%2C248%2C278&source=youtube&requiressl=yes&mh=wn&mm=31%2C26&mn=sn-n4v7sn7z%2Csn-a5mlrnes&ms=au%2Conr&mv=m&mvi=0&pl=16&initcwndbps=1668750&vprv=1&mime=video%2Fmp4&gir=yes&clen=97184468&dur=322.355&lmt=1454048319655424&mt=1585269331&fvip=1&keepalive=yes&c=WEB&sparams=expire%2Cei%2Cip%2Cid%2Caitags%2Csource%2Crequiressl%2Cvprv%2Cmime%2Cgir%2Cclen%2Cdur%2Clmt&sig=ADKhkGMwRQIhAOwwqYM3z_3XXS4cHtmnFx2eLlkTVbWoYvE95W8zGri6AiBPeJFq_dfgtMk6INpjgK7UPV_sfojACHxo401SQA4y5A%3D%3D&lsparams=mh%2Cmm%2Cmn%2Cms%2Cmv%2Cmvi%2Cpl%2Cinitcwndbps&lsig=ABSNjpQwRgIhAPJWvfsduclTwb1q4-6XhwSgPmue1E97fMmfemYFGXR1AiEA0WACdFiWPjMCEaXV9Rlu--29F-l6xuSADqnuXrV0FXU%3D&ratebypass=yes'
[download] Neil Tyson & Steven Tyler Talking Science Backstage at The Late Show with Stephen Colbert-AeUPQa5H8BI.f137.mp4 has already been downloaded
[download] 100% of 92.68MiB
[debug] Invoking downloader on 'https://r1---sn-n4v7sn7z.googlevideo.com/videoplayback?expire=1585291042&ei=wkp9XvbnB47TkgaF14TQDg&ip=98.176.94.192&id=o-AJNzsLN2X_qYEkviNJRUwP70l6GenJE6yV_QPjNMRBbz&itag=251&source=youtube&requiressl=yes&mh=wn&mm=31%2C26&mn=sn-n4v7sn7z%2Csn-a5mlrnes&ms=au%2Conr&mv=m&mvi=0&pl=16&initcwndbps=1668750&vprv=1&mime=audio%2Fwebm&gir=yes&clen=4163935&dur=322.361&lmt=1453919618044996&mt=1585269331&fvip=1&keepalive=yes&c=WEB&sparams=expire%2Cei%2Cip%2Cid%2Citag%2Csource%2Crequiressl%2Cvprv%2Cmime%2Cgir%2Cclen%2Cdur%2Clmt&sig=ADKhkGMwRQIgYXROhvl0eKTwOwswHlJ8mFKeN7UsRwdb22IOreXQJO0CIQCSzKzljFjcei8QPp50T0E2CMPAYbc2XiPeL10ZDy_zuw%3D%3D&lsparams=mh%2Cmm%2Cmn%2Cms%2Cmv%2Cmvi%2Cpl%2Cinitcwndbps&lsig=ABSNjpQwRgIhAPJWvfsduclTwb1q4-6XhwSgPmue1E97fMmfemYFGXR1AiEA0WACdFiWPjMCEaXV9Rlu--29F-l6xuSADqnuXrV0FXU%3D&ratebypass=yes'
[download] Neil Tyson & Steven Tyler Talking Science Backstage at The Late Show with Stephen Colbert-AeUPQa5H8BI.f251.webm has already been downloaded
[download] 100% of 3.97MiB
[ffmpeg] Merging formats into "Neil Tyson & Steven Tyler Talking Science Backstage at The Late Show with Stephen Colbert-AeUPQa5H8BI.mp4"
[debug] ffmpeg command line: ffmpeg -y -loglevel "repeat+info" -i "file:Neil Tyson & Steven Tyler Talking Science Backstage at The Late Show with Stephen Colbert-AeUPQa5H8BI.f137.mp4" -i "file:Neil Tyson & Steven Tyler Talking Science Backstage at The Late Show with Stephen Colbert-AeUPQa5H8BI.f251.webm" -c copy -map "0:v:0" -map "1:a:0" "file:Neil Tyson & Steven Tyler Talking Science Backstage at The Late Show with Stephen Colbert-AeUPQa5H8BI.temp.mp4"
ERROR: file:Neil Tyson & Steven Tyler Talking Science Backstage at The Late Show with Stephen Colbert-AeUPQa5H8BI.f137.mp4: No such file or directory
Traceback (most recent call last):
  File "C:\Users\dst\AppData\Roaming\Build archive\youtube-dl\ytdl-org\tmp378onz6j\build\youtube_dl\YoutubeDL.py", line 2065, in post_process
  File "C:\Users\dst\AppData\Roaming\Build archive\youtube-dl\ytdl-org\tmp378onz6j\build\youtube_dl\postprocessor\ffmpeg.py", line 512, in run
  File "C:\Users\dst\AppData\Roaming\Build archive\youtube-dl\ytdl-org\tmp378onz6j\build\youtube_dl\postprocessor\ffmpeg.py", line 235, in run_ffmpeg_multiple_files
youtube_dl.postprocessor.ffmpeg.FFmpegPostProcessorError: file:Neil Tyson & Steven Tyler Talking Science Backstage at The Late Show with Stephen Colbert-AeUPQa5H8BI.f137.mp4: No such file or directory