TOPIC:

Hi!

I'm new to FCPX, could someone point out the easiest way to create subtitles in HD without the black background that comes by default.

Many thanks in advance.

Not a good idea. It's there for a reason.

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If you insist going that direction simply overlay as a 'title'.
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This is another option where text is outlined but you'll definitely need foreground/background separation for legibility.
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Here's something I've been toying with.... MacWhisper (free version). A speech to text app for doing subtitles. No uploading anywhere. All data stays local. Does a remarkable job. I'll run off an initial SRT file and let the client verify word accuracy & make corrections.
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Here's something I just ran through Compressor which is the first time I've had it do subs. Very promising.
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The beauty of generating SRT files on projects you have no interest in captioning is doing a search which'll zero in where a word or name was mentioned without having to scrub through video.