ffmpeg -i in.mp4 -filter_complex "[0:v]setpts=2*PTS[v];[0:a]atempo=0.5[a]" -map "[v]" -map "[a]"  -c:v libx264 -preset slow -crf 0 -c:a libmp3lame -q:a 0 out.mp4ffmpeg -i in.mp4 -filter_complex "[0:v]setpts=2*PTS[v];[0:a]atempo=0.5[a]" -map "[v]" -map "[a]"  -c:v libx264 -preset slow -crf 0 -c:a libmp3lame -q:a 0 out.mp4