With youtube-dl I first look what video quality is available and then in second step I download highest possible quality (in this example -f 137+140). Youtube-dl will automatically merge audio and video stream (DASH format)
How to automate that with shell script? Too choose with every video highest audio and video quality?
> youtube-dl -F 'https://www.youtube.com/watch?v=VAdRBLyjLRQ&feature=youtu.be&t=8m14s'
[youtube] Downloading login page
[youtube] Logging in
[youtube] VAdRBLyjLRQ: Downloading webpage
[youtube] VAdRBLyjLRQ: Downloading video info webpage
[youtube] VAdRBLyjLRQ: Extracting video information
[youtube] VAdRBLyjLRQ: Downloading DASH manifest
[youtube] VAdRBLyjLRQ: Downloading DASH manifest
[info] Available formats for VAdRBLyjLRQ:
format code extension resolution note
249 webm audio only DASH audio , opus @ 50k
250 webm audio only DASH audio , opus @ 70k
251 webm audio only DASH audio , opus @160k
171 webm audio only DASH audio 117k , vorbis@128k (44100Hz), 7.68MiB
140 m4a audio only DASH audio 128k , m4a_dash container, aac @128k (44100Hz), 11.58MiB
160 mp4 256x144 DASH video 112k , avc1.4d400c, 15fps, video only, 9.94MiB
278 webm 256x144 DASH video 136k , webm container, VP9, 15fps, video only, 9.10MiB
133 mp4 426x240 DASH video 248k , avc1.4d4015, 30fps, video only, 22.27MiB
242 webm 426x240 DASH video 316k , vp9, 30fps, video only, 22.20MiB
243 webm 640x360 DASH video 557k , vp9, 30fps, video only, 41.05MiB
134 mp4 640x360 DASH video 609k , avc1.4d401e, 30fps, video only, 52.94MiB
244 webm 854x480 DASH video 1021k , vp9, 30fps, video only, 74.05MiB
135 mp4 854x480 DASH video 1115k , avc1.4d401f, 30fps, video only, 97.02MiB
247 webm 1280x720 DASH video 2011k , vp9, 30fps, video only, 150.61MiB
136 mp4 1280x720 DASH video 2282k , avc1.4d401f, 30fps, video only, 189.40MiB
248 webm 1920x1080 DASH video 3838k , vp9, 30fps, video only, 286.61MiB
137 mp4 1920x1080 DASH video 4209k , avc1.640028, 30fps, video only, 354.19MiB
17 3gp 176x144
36 3gp 320x240
5 flv 400x240
43 webm 640x360
18 mp4 640x360
22 mp4 1280x720 (best)
> youtube-dl -f 137+140 'https://www.youtube.com/watch?v=VAdRBLyjLRQ&feature=youtu.be&t=8m14s'
[youtube] Downloading login page
[youtube] Logging in
[youtube] VAdRBLyjLRQ: Downloading webpage
[youtube] VAdRBLyjLRQ: Downloading video info webpage
[youtube] VAdRBLyjLRQ: Extracting video information
(...)
Just use -f bestvideo+bestaudio/best for highest resulting quality available.
If you wanted to prefer MP4 format containers instead of WebM, use:
-f bestvideo[ext!=webm]+bestaudio[ext!=webm]/best[ext!=webm].
I've found some weird cases where the default (see #5447, #5456) bestvideo+bestaudio/best would download 720p video even when a 1080p was available. The reason that the bitrate on the 720p was very slightly higher, therefore it seemed better quality for youtube-dl. I prefer the higher res, also all other fancy youtube downloader applications downloaded the 1080p (as control).
Therefore I propose and use this:
-f ("bestvideo[width>=1920]"/bestvideo)+bestaudio/best
It will look for the best, at least 1920 wide video. If that's not available, it'll resort to what it would normally choose. The /best part at the end is part of the default config.
On a side note I recommend putting the %(format_id)s somewhere in the filename, so you know what that file is using. If you later want to re-download a bunch of videos without using archive, with --no-overwrites, a better/different quality will form a new filename next to the old one (so you can compare or whatever).
Or you could just use,
youtube-dl https://www.youtube.com/watch?v=blabla
This will download the highest quality video and audio and merge them automatically. And I think I have heard somewhere that you need ffmpeg installed to have this automatic behavior. But I bet most systems have it already.
Since the numbers of format are limited I did:
youtube-dl -f 299+140 "http://www.youtube.com/watch?v=P9pzm5b6FFY"
youtube-dl -f 137+140 "http://www.youtube.com/watch?v=P9pzm5b6FFY"
youtube-dl -f best "http://www.youtube.com/watch?v=P9pzm5b6FFY"
If the 299+140 has been downloaded the 137+140 won't be and if none of those have you'll have the best starting with 22. The only problem is that you'll have the best in webm as a duplicate but you can use the ext!=webm to avoid this.
Of course you can start at 313+140 or whatever higher format you want.
Check the available formats for that particular video using this :
youtube-dl -F video-url
Download the video using this :
youtube-dl -f code video-url
Example ::
youtube-dl -F "http://www.youtube.com/watch?v=P9pzm5b6FFY"
Here’s the output:
[youtube] Setting language
[youtube] P9pzm5b6FFY: Downloading webpage
[youtube] P9pzm5b6FFY: Downloading video info webpage
[youtube] P9pzm5b6FFY: Extracting video information
[info] Available formats for P9pzm5b6FFY:
format code extension resolution note
140 m4a audio only DASH audio , audio@128k (worst)
160 mp4 144p DASH video , video only
133 mp4 240p DASH video , video only
134 mp4 360p DASH video , video only
135 mp4 480p DASH video , video only
136 mp4 720p DASH video , video only
17 3gp 176x144
36 3gp 320x240
5 flv 400x240
43 webm 640x360
18 mp4 640x360
22 mp4 1280x720 (best)
then perform this to download video for 1280*720 pixels ::
youtube-dl -f 22 "http://www.youtube.com/watch?v=P9pzm5b6FFY"
来源：https://stackoverflow.com/questions/31631535/youtube-dl-dash-video-and-audio-in-highest-quality-without-human-intervention