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.
If the input and output filenames don't contain spaces, quotation marks or other special characters:
ffmpeg -i input.webm -c:v libx264 -preset slow -crf 22 -c:a aac -b:a 128k output.mp4
