indent json with --pretty-json

[knighthat]

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• Read youtube-dl coding conventions and adjusted the code to meet them
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What is the purpose of your pull request?

• Bug fix
• Improvement
• New extractor
• New feature

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Description of your pull request and other information

This switch --pretty-json prints result of --dump-json in a more human readable format. Applicable in storing video's information.

Reason: I am making a wrapper called youtube-dl-java. Loading 1 line of JSON with hundreds of thousands of characters takes a significantly long time due to how much memory is allocated for 1 single line.

This also makes it easier for users to inspect the return json since it's nicely indented.

[dirkf]

Thanks for your proposal.

I don't think we should add a feature just to help your programming project. Instead, ask whether you are loading the JSON into your Java program efficiently, or why Python can handle files of this sort (eg, --load-info-json) without complaint. There seem to be quite a few libraries dedicated to doing this for Java.

Also, there are many external tools available for JS[ON] parsing and beautification, such as jq.

[knighthat]

The main purpose of this feature is to let user save outputs to physical file. There are tools out there and I'm using it daily too but why do I have to install or write a script to parse it when python can just do the same?

Btw, copying 1 line of string with hundreds of thousands of characters is a real pain.