Getting "ERROR:libpostproc", but resulting m4a seems to play fine.

[sunk818]

c:>youtube-dl -f 140 https://www.youtube.com/watch?v=MxpLlNHAjRI

[youtube] MxpLlNHAjRI: Downloading webpage
[youtube] MxpLlNHAjRI: Downloading video info webpage
[youtube] MxpLlNHAjRI: Extracting video information
[youtube] MxpLlNHAjRI: Downloading MPD manifest
[download] Destination: Jurassic 5 - In The House (Nightmares on Wax Remix)-MxpLlNHAjRI.m4a
[download] 100% of 4.41MiB in 00:00
[ffmpeg] Correcting container in "Jurassic 5 - In The House (Nightmares on Wax Remix)-MxpLlNHAjRI.m4a"
ERROR:   libpostproc    54.  0.100 / 54.  0.100

[dstftw]

Post the full output of youtube-dl when run with -v, i.e. add -v flag to your command line, copy the whole output and post it in the issue body wrapped in ``` for better formatting. It should look similar to this:

$ youtube-dl -v <your command line>
[debug] System config: []
[debug] User config: []
[debug] Command-line args: [u'-v', u'http://www.youtube.com/watch?v=BaW_jenozKcj']
[debug] Encodings: locale cp1251, fs mbcs, out cp866, pref cp1251
[debug] youtube-dl version 2015.12.06
[debug] Git HEAD: 135392e
[debug] Python version 2.6.6 - Windows-2003Server-5.2.3790-SP2
[debug] exe versions: ffmpeg N-75573-g1d0487f, ffprobe N-75573-g1d0487f, rtmpdump 2.4
[debug] Proxy map: {}
...

Do not post screenshots of verbose log only plain text is acceptable.

The output (including the first lines) contains important debugging information. Issues without the full output are often not reproducible and therefore do not get solved in short order, if ever.

[sunk818]

Seems to be fine now. Maybe it was a YouTube glitch.

C:>youtube-dl -v -f 140 https://www.youtube.com/watch?v=MxpLlNHAjRI
[debug] System config: []
[debug] User config: []
[debug] Command-line args: [u'-v', u'-f', u'140', u'https://www.youtube.com/watch?v=MxpLlNHAjRI']
[debug] Encodings: locale cp1252, fs mbcs, out cp1252, pref cp1252
[debug] youtube-dl version 2016.02.22
[debug] Python version 2.7.10 - Windows-7-6.1.7601-SP1
[debug] exe versions: ffmpeg 2.8.6, ffprobe 2.8.6, rtmpdump 2.4
[debug] Proxy map: {}
[youtube] MxpLlNHAjRI: Downloading webpage
[youtube] MxpLlNHAjRI: Downloading video info webpage
[youtube] MxpLlNHAjRI: Extracting video information
[youtube] MxpLlNHAjRI: Downloading MPD manifest
[debug] Invoking downloader on u'https://r16---sn-a5m7lnek.googlevideo.com/videoplayback?id=331a4b94d1c08d12&itag=140&source=youtube&requiressl=yes&mv=m&pl=16&ms=au&mn=sn-a5m7lnek&mm=31&gcr=us&nh=IgpwcjAxLmxheDAyKgkxMjcuMC4wLjE&ratebypass=yes&mime=au
dio/mp4&gir=yes&clen=4621794&lmt=1402035907270002&dur=287.834&mt=1456430986&signature=0B5E43D92FBFBCCF8A0321231E0A842589EDA512.31BA79CED5EFD535DB618EE9B7E8E33B477F997F&sver=3&fexp=9413278,9416126,9416903,9420452,9421339,9421501,9422596,9423341,942366
1,9423662,9426047,9426657,9427110,9428650,9429232,9429610&upn=7YC4DmzyxFo&key=dg_yt0&ip=153.10.242.1&ipbits=0&expire=1456452705&sparams=ip,ipbits,expire,id,itag,source,requiressl,mv,pl,ms,mn,mm,gcr,nh,ratebypass,mime,gir,clen,lmt,dur'
[download] Destination: Jurassic 5 - In The House (Nightmares on Wax Remix)-MxpLlNHAjRI.m4a
[download] 100% of 4.41MiB in 00:00
[ffmpeg] Correcting container in "Jurassic 5 - In The House (Nightmares on Wax Remix)-MxpLlNHAjRI.m4a"
[debug] ffmpeg command line: ffmpeg -y -i 'file:Jurassic 5 - In The House (Nightmares on Wax Remix)-MxpLlNHAjRI.m4a' -c copy -f mp4 'file:Jurassic 5 - In The House (Nightmares on Wax Remix)-MxpLlNHAjRI.temp.m4a'