YouTube thumbnails - inconsistent behavior (webp, jpg)

[misc01]

Checklist

• I'm reporting a broken site support
• I've verified that I'm running youtube-dl version 2020.06.16.1
• I've checked that all provided URLs are alive and playable in a browser
• I've checked that all URLs and arguments with special characters are properly quoted or escaped
• I've searched the bugtracker for similar issues including closed ones

Description

Problem 1:

For some YouTube videos youtube-dl downloads the webp thumbnail image and for some the jpg version.

Example 1: youtube-dl downloads the webp version

youtube-dl -v --skip-download --write-thumbnail https://www.youtube.com/watch?v=HOYDj769s6k
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['-v', '--skip-download', '--write-thumbnail', 'https://www.youtube.com/watch?v=HOYDj769s6k']
[debug] Encodings: locale UTF-8, fs utf-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2020.06.16.1
[debug] Python version 3.7.7 (CPython) - Darwin-16.7.0-x86_64-i386-64bit
[debug] exe versions: ffmpeg 4.1.3-tessus, ffprobe 4.1.3-tessus, rtmpdump 2.4-81-20130413
[debug] Proxy map: {}
[youtube] HOYDj769s6k: Downloading webpage
[debug] Default format spec: bestvideo+bestaudio/best
[youtube] HOYDj769s6k: Downloading thumbnail ...
[youtube] HOYDj769s6k: Writing thumbnail to: Titan Missile Explosion HD-HOYDj769s6k.webp

youtube-dl -v --list-thumbnails https://www.youtube.com/watch?v=HOYDj769s6k
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['-v', '--list-thumbnails', 'https://www.youtube.com/watch?v=HOYDj769s6k']
[debug] Encodings: locale UTF-8, fs utf-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2020.06.16.1
[debug] Python version 3.7.7 (CPython) - Darwin-16.7.0-x86_64-i386-64bit
[debug] exe versions: ffmpeg 4.1.3-tessus, ffprobe 4.1.3-tessus, rtmpdump 2.4-81-20130413
[debug] Proxy map: {}
[youtube] HOYDj769s6k: Downloading webpage
[info] Thumbnails for HOYDj769s6k:
ID  width  height URL
0   168    94     https://i.ytimg.com/vi/HOYDj769s6k/hqdefault.jpg?sqp=-oaymwEYCKgBEF5IVfKriqkDCwgBFQAAiEIYAXAB&rs=AOn4CLAYRe2URm7RNAImwl0YtWaQz6kdXg
1   196    110    https://i.ytimg.com/vi/HOYDj769s6k/hqdefault.jpg?sqp=-oaymwEYCMQBEG5IVfKriqkDCwgBFQAAiEIYAXAB&rs=AOn4CLBTNRoS2jsUAcoZaMlKUmvZOU4ycQ
2   246    138    https://i.ytimg.com/vi/HOYDj769s6k/hqdefault.jpg?sqp=-oaymwEZCPYBEIoBSFXyq4qpAwsIARUAAIhCGAFwAQ==&rs=AOn4CLBU_li8ovx-NVuAm-diwhvWOBC_wQ
3   336    188    https://i.ytimg.com/vi/HOYDj769s6k/hqdefault.jpg?sqp=-oaymwEZCNACELwBSFXyq4qpAwsIARUAAIhCGAFwAQ==&rs=AOn4CLA8WI7mEyzbIEOBa9sk6K_RhKzc_w
4   1920   1080   https://i.ytimg.com/vi_webp/HOYDj769s6k/maxresdefault.webp

Example 2: youtube-dl downloads the jpg version

youtube-dl -v --skip-download --write-thumbnail https://www.youtube.com/watch?v=xgbPSA94Rqg
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['-v', '--skip-download', '--write-thumbnail', 'https://www.youtube.com/watch?v=xgbPSA94Rqg']
[debug] Encodings: locale UTF-8, fs utf-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2020.06.16.1
[debug] Python version 3.7.7 (CPython) - Darwin-16.7.0-x86_64-i386-64bit
[debug] exe versions: ffmpeg 4.1.3-tessus, ffprobe 4.1.3-tessus, rtmpdump 2.4-81-20130413
[debug] Proxy map: {}
[youtube] xgbPSA94Rqg: Downloading webpage
[debug] Default format spec: bestvideo+bestaudio/best
[youtube] xgbPSA94Rqg: Downloading thumbnail ...
[youtube] xgbPSA94Rqg: Writing thumbnail to: Foundation — Teaser _ Apple TV+-xgbPSA94Rqg.jpg

youtube-dl -v --list-thumbnails https://www.youtube.com/watch?v=xgbPSA94Rqg
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['-v', '--list-thumbnails', 'https://www.youtube.com/watch?v=xgbPSA94Rqg']
[debug] Encodings: locale UTF-8, fs utf-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2020.06.16.1
[debug] Python version 3.7.7 (CPython) - Darwin-16.7.0-x86_64-i386-64bit
[debug] exe versions: ffmpeg 4.1.3-tessus, ffprobe 4.1.3-tessus, rtmpdump 2.4-81-20130413
[debug] Proxy map: {}
[youtube] xgbPSA94Rqg: Downloading webpage
[info] Thumbnails for xgbPSA94Rqg:
ID  width  height URL
0   168    94     https://i.ytimg.com/vi/xgbPSA94Rqg/hqdefault.jpg?sqp=-oaymwEYCKgBEF5IVfKriqkDCwgBFQAAiEIYAXAB&rs=AOn4CLCDLQeMBm-5IWjsjFPJZM9ltD4D8g
1   196    110    https://i.ytimg.com/vi/xgbPSA94Rqg/hqdefault.jpg?sqp=-oaymwEYCMQBEG5IVfKriqkDCwgBFQAAiEIYAXAB&rs=AOn4CLAhsYAYOoofDMmGpQUC4X9r86JiBg
2   246    138    https://i.ytimg.com/vi/xgbPSA94Rqg/hqdefault.jpg?sqp=-oaymwEZCPYBEIoBSFXyq4qpAwsIARUAAIhCGAFwAQ==&rs=AOn4CLAwp3KPVC2kYHqfoDHLKiJixDVYfg
3   336    188    https://i.ytimg.com/vi/xgbPSA94Rqg/hqdefault.jpg?sqp=-oaymwEZCNACELwBSFXyq4qpAwsIARUAAIhCGAFwAQ==&rs=AOn4CLAxzSozHuaotJs_qsv5zHTpASat1g
4   1280   720    https://i.ytimg.com/vi/xgbPSA94Rqg/maxresdefault.jpg

In both cases a jpg and webp thumbnail is available:

https://i.ytimg.com/vi/HOYDj769s6k/maxresdefault.jpg
https://i.ytimg.com/vi_webp/HOYDj769s6k/maxresdefault.webp

https://i.ytimg.com/vi/xgbPSA94Rqg/maxresdefault.jpg
https://i.ytimg.com/vi_webp/xgbPSA94Rqg/maxresdefault.webp

Could youtube-dl offer an option to select the preferred thumbnail version?

Problem 2:

For videos without a high-resolution thumbnail youtube-dl downloads a webp thumbnail and names the file .jpg

youtube-dl -v --skip-download --write-thumbnail https://www.youtube.com/watch?v=fgxaD7u28A4
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['-v', '--skip-download', '--write-thumbnail', 'https://www.youtube.com/watch?v=fgxaD7u28A4']
[debug] Encodings: locale UTF-8, fs utf-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2020.06.16.1
[debug] Python version 3.7.7 (CPython) - Darwin-16.7.0-x86_64-i386-64bit
[debug] exe versions: ffmpeg 4.1.3-tessus, ffprobe 4.1.3-tessus, rtmpdump 2.4-81-20130413
[debug] Proxy map: {}
[youtube] fgxaD7u28A4: Downloading webpage
[debug] Default format spec: bestvideo+bestaudio/best
[youtube] fgxaD7u28A4: Downloading thumbnail ...
[youtube] fgxaD7u28A4: Writing thumbnail to: Joe Rogan Experience #1496 - Colion Noir-fgxaD7u28A4.jpg

This is a webp image, not a jpg.

youtube-dl -v --list-thumbnails https://www.youtube.com/watch?v=fgxaD7u28A4
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['-v', '--list-thumbnails', 'https://www.youtube.com/watch?v=fgxaD7u28A4']
[debug] Encodings: locale UTF-8, fs utf-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2020.06.16.1
[debug] Python version 3.7.7 (CPython) - Darwin-16.7.0-x86_64-i386-64bit
[debug] exe versions: ffmpeg 4.1.3-tessus, ffprobe 4.1.3-tessus, rtmpdump 2.4-81-20130413
[debug] Proxy map: {}
[youtube] fgxaD7u28A4: Downloading webpage
[info] Thumbnails for fgxaD7u28A4:
ID  width  height URL
0   168    94     https://i.ytimg.com/vi/fgxaD7u28A4/hqdefault.jpg?sqp=-oaymwEYCKgBEF5IVfKriqkDCwgBFQAAiEIYAXAB&rs=AOn4CLBYHOi3blqAF3gtLHAejQkGXSUNdQ
1   196    110    https://i.ytimg.com/vi/fgxaD7u28A4/hqdefault.jpg?sqp=-oaymwEYCMQBEG5IVfKriqkDCwgBFQAAiEIYAXAB&rs=AOn4CLANsTTbKz8u1QiqQD72-ijoIZkWng
2   246    138    https://i.ytimg.com/vi/fgxaD7u28A4/hqdefault.jpg?sqp=-oaymwEZCPYBEIoBSFXyq4qpAwsIARUAAIhCGAFwAQ==&rs=AOn4CLChFuzRwpmGvIu0Arg5AoOAuMAWbA
3   336    188    https://i.ytimg.com/vi/fgxaD7u28A4/hqdefault.jpg?sqp=-oaymwEZCNACELwBSFXyq4qpAwsIARUAAIhCGAFwAQ==&rs=AOn4CLDWQvTzlHvbONfWI3W1jT-ch_Mz-A

[dstftw]

This is what served by Youtube.

[DIERSON]

When will YOUTUBE-DL be updated so that MP3s can have thumbnails?