If you need to extract the audio from an .WEBM movie file to an .AAC audio file you can execute the following:
FILE="the-file-you-want-to-process.webm";
ffmpeg -i "${FILE}" -vn -ab 128k -ar 44100 -strict -2 -y "${FILE%.webm}.aac";
The first command will assign the file name to a variable, we do this to avoid typing errors in the second command where we might want to use the same name for the audio file.
The second command, will use ffmpeg to extract the audio. The -i flag, indicates the file name of the input. We used the flag -vn that will instruct ffmpeg to disable video recording. The -ab flag will set the bit rate to 128k. The -ar flag will set the audio sample rate to 441000 Hz. The flags -strict -2 are required as the native FFmpeg AAC encoder that is included with ffmpeg is considered an experimental encoder. The -y flag will overwrite output file without asking, so be careful when you use it.
In case we want to automatically process (batch process) all .WEBM video files in a folder we can use the following:
for FILE in *.webm; do
echo -e "Processing video '\e[32m$FILE\e[0m'";
ffmpeg -i "${FILE}" -vn -ab 128k -ar 44100 -strict -2 -y "${FILE%.webm}.aac";
done;
The above script will find all .WEBM files in the folder and process them one after the other.
UPDATE:
The following command will find all webm files that are in the current directory and in all sub-folders and extract the audio to aac format.
find . -type f -iname "*.webm" -exec bash -c 'FILE="$1"; ffmpeg -i "${FILE}" -vn -ab 128k -ar 44100 -strict -2 -y "${FILE%.webm}.aac";' _ '{}' \;
The filename of the audio file will be the same as the webm video with the correct extension. The webm extension will be removed and replaced by the aac extension e.g hi.webm will become hi.aac