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ffmpeg -i input.webm -c:v libx264 -preset slow -crf 22 -c:a aac -b:a 128k output.mp4

This ffmpeg command converts a .webm video file to a standard .mp4 file using the libx264 codec for video, aac codec for audio, and a CRF value of 22. The preset is set to 'slow' for higher quality encoding, and the audio bitrate is set to 128 kbps.

The ngx_http_core_module module supports embedded variables with names matching the Apache Server variables. First of all, these are variables representing client request header fields, such as $http_user_agent, $http_cookie, and so on. Also there are other variables:

• $arg_name
  argument name in the request line