When using subprocess passthrough is not accepting both inputs

Im trying to have two subprocesses pipe into one and output via the passthrough. My goal is to make it possible to download 2 files (one video and one audio) and combine them with ffmpeg.

header('Content-Description: File Transfer');  header('Cache-Control: must-revalidate');  header('Pragma: public');  header("Content-Disposition: attachment; filename=\"ok.mp4\"");  header("Content-Type: application/octet-stream");    $cmd = "<(youtube-dl -f bestvideo[ext=mp4] --no-part --no-cache-dir --no-warnings --no-progress -o - https://www.youtube.com/watch?v=6Dh-RL__uN4) <(youtube-dl -f bestaudio[ext=m4a] --no-part --no-cache-dir --no-warnings --no-progress -o - https://www.youtube.com/watch?v=6Dh-RL__uN4) | ffmpeg -i - -i pipe:3 -movflags frag_keyframe+empty_moov+faststart -frag_duration 3600 -c:v copy -c:a copy -f mp4 -";    $cmd = passthru($cmd, $status);  

My error is: -bash: /dev/fd/63: Permission denied

https://stackoverflow.com/questions/65820232/when-using-subprocess-passthrough-is-not-accepting-both-inputs January 21, 2021 at 10:06AM