[YouTube] "bestvideo" doesn't choose the actual best video in rare cases

[fireattack]

Please follow the guide below

• You will be asked some questions and requested to provide some information, please read them carefully and answer honestly
• Put an x into all the boxes [ ] relevant to your issue (like that [x])
• Use Preview tab to see how your issue will actually look like

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Make sure you are using the latest version: run youtube-dl --version and ensure your version is 2017.02.17. 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 Issues with outdated version will be rejected.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 2017.02.17

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• At least skimmed through README and most notably FAQ and BUGS sections
• Searched the bugtracker for similar issues including closed ones

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)
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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:

Add -v flag to your command line you run youtube-dl with, copy the whole output and insert it here. It should look similar to one below (replace it with your log inserted between triple ```):

D:\YouTube>youtube-dl https://www.youtube.com/watch?v=iMhwshjSauo -v -F
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['https://www.youtube.com/watch?v=iMhwshjSauo', '-v',
 '-F']
[debug] Encodings: locale cp936, fs mbcs, out cp936, pref cp936
[debug] youtube-dl version 2017.02.17
[debug] Python version 3.4.4 - Windows-7-6.1.7601-SP1
[debug] exe versions: ffmpeg N-83133-ge664730
[debug] Proxy map: {}
[youtube] iMhwshjSauo: Downloading webpage
[youtube] iMhwshjSauo: Downloading video info webpage
[youtube] iMhwshjSauo: Extracting video information
[youtube] {43} signature length 82.1.0, html5 player en_US-vflg9Wu9U
[youtube] {18} signature length 82.1.0, html5 player en_US-vflg9Wu9U
[youtube] {36} signature length 82.1.0, html5 player en_US-vflg9Wu9U
[youtube] {17} signature length 82.1.0, html5 player en_US-vflg9Wu9U
[youtube] iMhwshjSauo: Downloading MPD manifest
[info] Available formats for iMhwshjSauo:
format code  extension  resolution note
140          m4a        audio only DASH audio  129k , m4a_dash container, mp4a.4
0.2@128k (44100Hz)
134          mp4        540x360    DASH video  106k , avc1.4d401e, 30fps, video
only
160          mp4        216x144    DASH video  108k , avc1.4d400b, 30fps, video
only
135          mp4        720x480    DASH video  198k , avc1.4d401e, 30fps, video
only
133          mp4        360x240    DASH video  242k , avc1.4d400c, 30fps, video
only
17           3gp        176x144    small , mp4v.20.3, mp4a.40.2@ 24k
36           3gp        320x214    small , mp4v.20.3, mp4a.40.2
18           mp4        540x360    medium , avc1.42001E, mp4a.40.2@ 96k
43           webm       640x360    medium , vp8.0, vorbis@128k (best)

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Description of your issue, suggested solution and other information

It seems the bestvideo option purely chooses the format based on the bitrate. However, in rare cases, a higher quality/resolution video may have lower bitrates.

In this very example (note: video may not be available in the US), since the video is a still frame, the 480p DASH video ended up with only 198 kbps, while the 240p DASH video became 242 kbps, albeit having lower quality. And as a result, the bestvideo parameter chose the latter instead of the former that has better quality.

I think it's better to use resolution as an indicator of quality. At least on YouTube (IIRC), a higher resolution DASH video will always have better quality and is closer to the original file, since YouTube doesn't upscale videos.

[fireattack]

Wait a sec, something is weirder than I thought.

D:\YouTube>youtube-dl https://www.youtube.com/watch?v=iMhwshjSauo -f 135
[youtube] iMhwshjSauo: Downloading webpage
[youtube] iMhwshjSauo: Downloading video info webpage
[youtube] iMhwshjSauo: Extracting video information
[youtube] iMhwshjSauo: Downloading MPD manifest
[dashsegments] Total fragments: 45
[download] Destination: CoCo - はんぶん不思議 (CoCo1番!)-iMhwshjSauo.mp4
[download] 100% of 3.18MiB in 00:38

D:\YouTube>youtube-dl https://www.youtube.com/watch?v=iMhwshjSauo -f bestvideo
[youtube] iMhwshjSauo: Downloading webpage
[youtube] iMhwshjSauo: Downloading video info webpage
[youtube] iMhwshjSauo: Extracting video information
[youtube] iMhwshjSauo: Downloading MPD manifest
[dashsegments] Total fragments: 45
[download] Destination: CoCo - はんぶん不思議 (CoCo1番!)-iMhwshjSauo.mp4
[download] 100% of 973.70KiB in 00:33

As you can see here, the "bestvideo" (133 mp4 360x240 one) is only 973.70KiB. Its actual bitrate is 32.2 kbps (reported by mediainfo).

And the 480p one has a filesize of 3.18MiB, with actual bitrate 112 kbps.

So in short, all these bitrates are wrong to begin with.

[Hrxn]

Not necessarily wrong..

A better (i.e. more efficient) video encoding allows the same quality with a much lower bitrate, that's the point.

[fireattack]

Not necessarily, yeah. But in this particular case, the problem is bitrate is totally wrong to begin with