Default audio download isnt highest quality

[superlonglong]

Checklist

• [ x] I've verified that I'm running youtube-dl version 2019.06.21
• [x ] I've checked that all provided URLs are alive and playable in a browser
• [ x] I've checked that all URLs and arguments with special characters are properly quoted or escaped
• [x ] I've searched the bugtracker for similar bug reports including closed ones
• [ x] I've read bugs section in FAQ

Verbose log

PASTE VERBOSE LOG HERE

youtube-dl -v -x https://www.youtube.com/watch?v=o_zD1YCj2fk
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['-v', '-x', 'https://www.youtube.com/watch?v=o_zD1YC
j2fk']
[debug] Encodings: locale cp1252, fs mbcs, out cp850, pref cp1252
[debug] youtube-dl version 2019.06.21
[debug] Python version 3.4.4 (CPython) - Windows-7-6.1.7601-SP1
[debug] exe versions: none
[debug] Proxy map: {}
[youtube] o_zD1YCj2fk: Downloading webpage
[youtube] o_zD1YCj2fk: Downloading video info webpage
[youtube] {18} signature length 104, html5 player vfl49f_g4
[youtube] {137} signature length 104, html5 player vfl49f_g4
[youtube] {248} signature length 104, html5 player vfl49f_g4
[youtube] {136} signature length 104, html5 player vfl49f_g4
[youtube] {247} signature length 100, html5 player vfl49f_g4
[youtube] {135} signature length 104, html5 player vfl49f_g4
[youtube] {244} signature length 104, html5 player vfl49f_g4
[youtube] {134} signature length 100, html5 player vfl49f_g4
[youtube] {243} signature length 104, html5 player vfl49f_g4
[youtube] {133} signature length 100, html5 player vfl49f_g4
[youtube] {242} signature length 104, html5 player vfl49f_g4
[youtube] {160} signature length 104, html5 player vfl49f_g4
[youtube] {278} signature length 104, html5 player vfl49f_g4
[youtube] {140} signature length 100, html5 player vfl49f_g4
[youtube] {171} signature length 104, html5 player vfl49f_g4
[youtube] {249} signature length 104, html5 player vfl49f_g4
[youtube] {250} signature length 100, html5 player vfl49f_g4
[youtube] {251} signature length 104, html5 player vfl49f_g4
[debug] Invoking downloader on 'https://r2---sn-fpqxc5oq-hxae.googlevideo.com/vi
deoplayback?expire=1561370023&ei=R0kQXaWqEcHRz7sPiNiW4AE&ip=119.18.0.170&id=o-AO
t-8uBf-YuA5JvjB5QXrjkCAfUveEur8qvUfnsBGmVj&itag=171&source=youtube&requiressl=ye
s&mm=31%2C29&mn=sn-fpqxc5oq-hxae%2Csn-ntqe6n7k&ms=au%2Crdu&mv=m&pl=24&initcwndbp
s=2488750&mime=audio%2Fwebm&gir=yes&clen=2657363&dur=157.731&lmt=156085012590574
8&mt=1561348324&fvip=5&keepalive=yes&beids=9466585&c=WEB&txp=2301222&sparams=exp
ire%2Cei%2Cip%2Cid%2Citag%2Csource%2Crequiressl%2Cmime%2Cgir%2Cclen%2Cdur%2Clmt&
lsparams=mm%2Cmn%2Cms%2Cmv%2Cpl%2Cinitcwndbps&lsig=AHylml4wRAIgATSS0FtQcD2dJxvKV
on2KhhO2dqPFJOgR7F2W2qtEyQCIEQGZ2NRUCLxBI5gLLx41g3rju70oxB5G_drapRsunQ5&sig=ALgx
I2wwRQIhANQmBr1wbyJzwp_8_I1VyFuFKA_a61BR_vVcLXtJeK8sAiA1UUwcHMOn-Vx9jc2ZnACTpJ6x
8yxcj3gzDoQsViL9xg==&ratebypass=yes'
[download] blink 182 - What's My Age Again for Brass Quintet and Drums with shee
t music-o_zD1YCj2fk.webm has already been downloaded
[download] 100% of 2.53MiB
ERROR: ffprobe/avprobe and ffmpeg/avconv not found. Please install one.
Traceback (most recent call last):
File "C:\Users\dst\AppData\Roaming\Build archive\youtube-dl\ytdl-org\tmppgbwk_
g4\build\youtube_dl\YoutubeDL.py", line 2054, in post_process
File "C:\Users\dst\AppData\Roaming\Build archive\youtube-dl\ytdl-org\tmppgbwk_
g4\build\youtube_dl\postprocessor\ffmpeg.py", line 272, in run
File "C:\Users\dst\AppData\Roaming\Build archive\youtube-dl\ytdl-org\tmppgbwk_
g4\build\youtube_dl\postprocessor\ffmpeg.py", line 166, in get_audio_codec
youtube_dl.utils.PostProcessingError: ffprobe/avprobe and ffmpeg/avconv not foun
d. Please install one.

Description

-x chooses the largest file, not the highest bitrate.

Youtube has many different audio qualities for this song

https://www.youtube.com/watch?v=o_zD1YCj2fk

as seen in this -F

format code extension resolution note
249 webm audio only DASH audio 66k , opus @ 50k, 1.04MiB
250 webm audio only DASH audio 87k , opus @ 70k, 1.36MiB
140 m4a audio only DASH audio 130k , m4a_dash container, mp4a.40.2@128k, 2.44MiB
251 webm audio only DASH audio 160k , opus @160k, 2.62MiB
171 webm audio only DASH audio 162k , vorbis@128k, 2.53MiB

file chosen when you don't specify is the 128k vorbis, not the 160k opus. this punishes opus for being more efficient.

also, if youtube is being so kind as to wrap things up in .opus for us, we dont really need ffmpeg?

[dstftw]

It selects format with max total bitrate as reported by metadata that is 171.