`--simulate` doesn't accurately simulate downloading under certain conditions about yt-dlp HOT 5 OPEN

cc @dirkf

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I'm a little hazy as to why one would want to use --simulate because all it basically tells you is that the extractor didn't (with luck) crash. If you want to know, say, what format(s) will be selected there is--get-format or eqv. Since no video download is being run, it can't tell you anything about any external downloader.

Looking at upstream confirms the diagnosis in this issue.

1. The API param simulate is also forced to true when a "printing" option such as --get-format is selected. This would give the wrong answer if the default format selection was changed by simulate.

2. The default format is changed to best/bestvideo+bestaudio as below:

        def prefer_best():
            if self.params.get('simulate', False):
                return False
            if not download:
                return False
            if self.params.get('outtmpl', DEFAULT_OUTTMPL) == '-':
                return True
            if info_dict.get('is_live'):
                return True
            if not can_merge():
                return True
            return False

So actually there are several cases where the default format should be changed, and isn't, when simulate is set, or when no download is requested (normally not through the CLI). Arguably the first two tests should be moved after the tests that return True.

from yt-dlp.

I'm a little hazy as to why one would want to use --simulate because all it basically tells you is that the extractor didn't (with luck) crash. If you want to know, say, what format(s) will be selected there is --get-format or eqv.

Yeah, the issue is really about the simulate param rather than just the --simulate CLI flag

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Well, I think the third result (without the simulate/download tests) is correct and the second not:

$ python -m youtube_dl --get-format 'BaW_jenozKc'
248 - 1920x1080 (1080p)+140 - audio only (audio_quality_medium)
$ python -m youtube_dl --get-format -o - 'BaW_jenozKc'
248 - 1920x1080 (1080p)+140 - audio only (audio_quality_medium)
$ python -m youtube_dl --get-format -o - 'BaW_jenozKc'
22 - 1280x720 (720p)
$ 

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Re: 96da952#r141681868

In case users of the API rely on the historic behaviour when download is falsy, that can be left in place, as it's always truthy in the CLI (at least it is upstream).

Imo, since we are breaking compat anyway, it's more consistent to completely get rid of this behavior. Although not the recommended approach, I have often seen extract_info(URL, download=False) to get metadata and then download(URL) in the wild.

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