How do I make youtube-dl use standard output (Do not close instantly !!!!)

[WhoseTheNerd]

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Question

How can I use standard output to pipe output to another programs input. Like so:
$ youtube-dl -x --audio-format wav -o _ https://www.youtube.com/watch?v=n8X9_MgEdCg | sudo ./fm_transmitter -f 88.4 _, with error code Error: Cannot open _, file does not exist
How can I pipe youtube-dl output into ./fm_transmitter input?

[remitamine]

it's a dash not an undersore, -o - not -o _.

[WhoseTheNerd]

That will output an error youtube-dl: error: Cannot download a video and extract audio into the same file! Use "-.%(ext)s" instead of "-" as the output template. @remitamine

[remitamine]

which means that you can't extract audio and at the same time send it to standard output.