So, we set the audio codec to copy to prevent FFmpeg from automatically transcoding the stream. Every time you perform the encoding, you are modifying the stream a little (or maybe a lot). Since our codec is lossy, decoding a stream and re-encoding it will most probably result in a slightly different stream. So, if we just did:įFmpeg will decode the input stream, encode it into aac again then write it to the output file. Then, it transcodes the input into that format. FFmpeg normally tries to deduce the desired file format from the output file extension. To extract the audio stream:įfmpeg -i input.mp4 -map 0:1 -c:a copy output.aac Notice the audio codec ( aac) and the bitrate ( 71 kb/s). Our example file contains two streams, 0:0 (input file 0, stream number 0, which is video) and 0:1 (the audio stream we are about to extract). First, we discover the streams available and their order:įfmpeg version 2.8.8-0ubuntu0.16.04.1 Copyright (c) 2000-2016 the FFmpeg developers

One common scenario is extracting audio from a video.

Fluent ffmpeg write stream to variable