FFMPEG

Convert m4a to mp3:
    ffmpeg -i input.m4a -c:a libmp3lame -q:a 8 output.mp3

Convert .flv videos to .mp4"
    ffmpeg -i Videoname.flv -vcodec copy -acodec copy Videoname.mp4

Convert file1 to file2:
    ffmpeg -i $1 -vcodec copy -acodec copy $2

Convert mp4 to webm:
    ffmpeg -i test.mp4 -c:v libvpx-vp9 -crf 30 -b:v 0 -b:a 128k -c:a libopus test.webm

Bash script to convert multiple Sony mts files to mp4 files:
  
    ffmpegbatch(){
      if [ $# -ne 2 ]
      then
      echo .     Usage: ffmpegbatch MTS mp4
      else
      for f in *.$1;
      do
      ffmpeg -i $f -vcodec copy -acodec copy ${f%$1}$2;
      done
      fi
    }
  

Bash script to convert multiple .wav files to .mp3 and .ogg files:
Source: https://superuser.com/questions/373889/batch-convert-wav-to-mp3-and-ogg

    for f in *.{wav,WAV}; 
    do 
            ffmpeg -i "$f" -c:a libmp3lame -q:a 2 "${f%.*}.mp3" -c:a libvorbis -q:a 4 "${f%.*}.ogg"; 
    done