FFmpeg

Difference between file extensions wav, opus, m4a etc.

ffmpeg -i file1.m4a -ar 16000 -b:a 32000 -ac 1 file1.opus

ffmpeg -i file2.opus -ar 16000 -ac 1 file2.wav

if we need a mono channel we use ac -1 flag

if we need 16kHz we use -ar 16000 flag

will compress file using -b:a 32000 flag

ffmpeg -help
-ab bitrate         audio bitrate (please use -b:a)
-ar rate            set audio sampling rate (in Hz)
-ac channels        set number of audio channels

-ar is the frequency at which the amplitude is measured e.g. 16kHz. it measures the amplitude 16k times a second.

-ab the bitrate is about how that information is compressed, it's an approximate num-bits per second. that it tries to compress the information to.

It is my understanding that if we want to compress the file we will use -ab flag when using ffmpeg

If we need decompress then we need to use -ar flag when using ffmpeg

This table shows how file sizes can change depending what extension we need.

file	m4a size	opus size	wav size
file1	14M	1.3M	28M
file2	11M	2.6M	21M
file3	8.1M	1.8M	16M

ffmpeg -i f.opus  -f wav -ar 16000 -ac 1 - > res.wav

ffmpeg -i f.opus  -f wav -ar 16000 -ac 1 - |