The following are two common usages of FFMPEG.

The first command extracts an audio track from a video file in the exact format that it was multiplexed info the video file.

The second example shows how you can adjust the volume of an audio file with re-encoding.

ffmpeg -i input.mpg -map 0:1 -acodec copy -vn output.ac3
ffmpeg -i input.ac3 -filter:a “volume=10dB” output2.ac3

The following command converts an MP4 video to an MPEG video with high quality:

ffmpeg -i input.mp4 -c:v mpeg2video -q:v 5 -c:a mp2 -f vob output.mpg

FFMPEG can be used to convert a video from one format to another. Very often, the video itself to be converted is already encoded in an appropriate format. You just want to convert the container format.

In the following example, the source video is encoded in MPEG-2 in an MKV container. It will be converted to an MPG video. No re-encoding is required since the source video is already in the target format. You can also select one or more audio tracks during conversion if this is part of the requirements.

ffmpeg -i input.mkv -map 0:a:1 -map 0:v -c:v copy -c:a copy output.mpg

If you would like to extract a portion of a video without re-encoding, consider using FFMPEG. The following example illustrates a command to extract a video from the 24th minute line and for 4 minutes 8 seconds, keeping all audio tracks.

ffmpeg -i input.mp4 -c copy -ss 00:24:00.000 -t 00:04:08.000 -map 0:v -map 0:a output.mp4

The example above may result in blank video in the beginning. If it is more important to have the video than audio, the following can be used (which may cause blank audio in the beginning).

ffmpeg -ss 00:24:00.000 -i input.mp4 -c copy -t 00:04:08.000 -map 0:v -map 0:a output.mp4

The most accurate way to extract part of a video is to re-encode (without -c copy), which may result in loss of quality and takes longer to process. This article describes the topic in details.

Here is another use case for FFMPEG. In some projects, after you mixed and matched video and audio streams from different files, the resultant file may not have the default audio stream as desired. You can use the following command to set the default audio stream while you are mixing the video/audio streams.

ffmpeg -i movie.mkv -i audio.dts -map 0:v:0 -map 1:a:0 -map 0:a:0 -c copy -disposition:a:0 default -disposition:a:1 none movie_combined.mkv

Very often you would like to change the not-so-standard resolution of a video to some more common formats, e.g. 4:3 or 16:9. You can try using the following FFMPEG command to achieve this.

ffmpeg -i video_1920.mp4 -vf scale=640:480,setdar=4:3 video_640x480.mp4 -hide_banner

This is another example of using FFMPEG to manipulate video and audio files. In this case, one would like to replace the second audio stream in a video file by another audio file.

Here is the command you may want to try:

ffmpeg -i video.mkv -i audio.mp3 -map 0:v -map 0:a:0 -map 1:a -codec copy output.mkv

There is yet another common use of FFMPEG, i.e. adding a new audio track to an existing file which can be a video-only file or a video file already with an audio track. A use case will be adding a second audio track to a file already with video and sound. The following is an example of the command to add audio.dts audio track to an existing mkv file:

ffmpeg -i input.mkv -i audio.dts -map 0 -map 1 -c copy output.mkv