--simulate doesn't accurately simulate downloading under certain conditions #9843
Description
DO NOT REMOVE OR SKIP THE ISSUE TEMPLATE
- I understand that I will be blocked if I intentionally remove or skip any mandatory* field
Checklist
- I'm reporting a bug unrelated to a specific site
- I've verified that I have updated yt-dlp to nightly or master (update instructions)
- I've checked that all provided URLs are playable in a browser with the same IP and same login details
- I've checked that all URLs and arguments with special characters are properly quoted or escaped
- I've searched known issues and the bugtracker for similar issues including closed ones. DO NOT post duplicates
- I've read the guidelines for opening an issue
Provide a description that is worded well enough to be understood
When running a yt-dlp command with --simulate (and without an -f arg), the default format selection differs from an unsimulated run under any of these conditions:
- ffmpeg is not available
- the outtmpl is
- - the URL is for a livestream (and
--live-from-startwas not passed)
A dry-run/simulate option should actually simulate the behaviour that will occur when downloading.
This behaviour is currently undocumented. Either the behaviour should be changed or at the very least be documented.
Copying initial discussion: #9805 (comment)
It looks like we can trace this logic back to ytdl-org/youtube-dl@0017d9a
Back then, upstream's default format spec was only best if ffmpeg was not available. So a simulated run would result in a "requested formats not available" error if ffmpeg was not available and there was no combined video+audio format available. This simulate check seems to be added so that you could print json without having to manually pass -f bv+ba or -f bv etc in this scenario -- see the linked upstream PR
Provide verbose output that clearly demonstrates the problem
- Run your yt-dlp command with -vU flag added (
yt-dlp -vU <your command line>) - If using API, add
'verbose': TruetoYoutubeDLparams instead - Copy the WHOLE output (starting with
[debug] Command-line config) and insert it below
Complete Verbose Output
[debug] Command-line config: ['-vU', '--simulate', 'https://www.youtube.com/watch?v=2yJgwwDcgV8']
[debug] Encodings: locale cp1252, fs utf-8, pref cp1252, out utf-8, error utf-8, screen utf-8
[debug] yt-dlp version master@2024.04.28.221944 from yt-dlp/yt-dlp-master-builds [ac817bc83] (win_exe)
[debug] Python 3.8.10 (CPython AMD64 64bit) - Windows-10-10.0.22631-SP0 (OpenSSL 1.1.1k 25 Mar 2021)
[debug] exe versions: none
[debug] Optional libraries: Cryptodome-3.20.0, brotli-1.1.0, certifi-2024.02.02, curl_cffi-0.5.10, mutagen-1.47.0, requests-2.31.0, sqlite3-3.35.5, urllib3-2.2.1, websockets-12.0
[debug] Proxy map: {}
[debug] Request Handlers: urllib, requests, websockets, curl_cffi
[debug] Loaded 1810 extractors
[debug] Fetching release info: https://api.github.com/repos/yt-dlp/yt-dlp-master-builds/releases/latest
Latest version: master@2024.04.28.221944 from yt-dlp/yt-dlp-master-builds
yt-dlp is up to date (master@2024.04.28.221944 from yt-dlp/yt-dlp-master-builds)
[youtube] Extracting URL: https://www.youtube.com/watch?v=2yJgwwDcgV8
[youtube] 2yJgwwDcgV8: Downloading webpage
[youtube] 2yJgwwDcgV8: Downloading ios player API JSON
[youtube] 2yJgwwDcgV8: Downloading android player API JSON
WARNING: [youtube] Skipping player responses from android clients (got player responses for video "aQvGIIdgFDM" instead of "2yJgwwDcgV8")
[debug] Loading youtube-nsig.7d1f7724 from cache
[debug] [youtube] Decrypted nsig ZyUwo2vdMccktm7tN0 => ZvGvrjLHlKzcbw
[debug] Loading youtube-nsig.7d1f7724 from cache
[debug] [youtube] Decrypted nsig vYdxycJ0vBBgWEBA_9 => Etq9qDUH370hPg
[youtube] 2yJgwwDcgV8: Downloading m3u8 information
[debug] Sort order given by extractor: quality, res, fps, hdr:12, source, vcodec:vp9.2, channels, acodec, lang, proto
[debug] Formats sorted by: hasvid, ie_pref, quality, res, fps, hdr:12(7), source, vcodec:vp9.2(10), channels, acodec, lang, proto, size, br, asr, vext, aext, hasaud, id
[debug] Default format spec: bestvideo*+bestaudio/best
[info] 2yJgwwDcgV8: Downloading 1 format(s): 244+251