An Introduction to FFmpeg

February 15, 2022

Previous: Encoding Effort Overview | Next: Setting Up an Encoding Environment

Introduction
Usage
Examples
Conclusion
Resources

Introduction

FFmpeg is a complete, cross-platform solution to record, convert and stream audio and video. This solution includes a number of libraries and a set of programs for handling these media-related tasks. The ffmpeg program itself is a command line tool designed to process video and audio files. It is used in programs like Handbrake and iTunes and on platforms like YouTube. This program is the primary tool that we will use for our encoding efforts.

Remark: FFmpeg also includes a command line tool called ffprobe which displays media information. We can use this tool to help us verify our videos after encoding.

Usage

The basic idea of a command given to the ffmpeg command line tool is to read from an arbitrary number of input files and write to an arbitrary number of output files. The structure of a command is as follows:

ffmpeg "[global options]" "[input options]" -i input "[output options]" output

global options are shared among all FFmpeg tools and do many things from adjusting the logging level to showing information like the current version to listing available library tools. The full list of options can be found here. For our encoding efforts, use of global options is not a necessity but useful to know.

input options act on the input files. With input options we can block streams of an input file from being filtered or mapped to an output file. Behavior of seek arguments -ss, -t & -to are also affected by their placement as input or output options. The latter will be relevant to our encoding workflow.

-i input are the list of input files that we are performing some encoding process on for our output files. We will more often than not be acting on a single input source file to create our WebMs.

output options describe the encoding process acting on our input files to produce our output files. We will elaborate on these sets of options relevant to our encoding process later.

output are the list of output files of our encoding process. In our encoding process our output is a WebM file.

Examples

Let's highlight a few of the many things we can do using ffmpeg to give an idea of what it does and how it works!

Get information related to the file

ffmpeg -i input.mkv

Where the video file is named input.mkv in our current directory and the output is a listing of media information printed to the console.

Hide Banner

ffmpeg -hide_banner -i input.mkv

Where the listing of media information printed to the console removes information related to the FFmpeg build using global option -hide_banner.

Convert video to another format

ffmpeg -i input.mkv output.webm

Where the input file input.mkv is converted to the WebM format using default encoding settings.

Extract the subtitle stream from a source file

ffmpeg -i input.mkv -map 0:s:0 subtitles.ass

Where we are mapping the first subtitle stream to the first subtitle stream of the output file subtitles.ass using stream selection and implicitly ignoring other streams from the input by not mapping those as well.

Create a gif using a palette file

ffmpeg -i input.mkv -vf "palettegen=stats_mode=diff" palette.png

ffmpeg -i input.mkv -i palette.png -lavfi "paletteuse" -y output.gif

In the first command, we are creating palette.png using the palettegen filter. In the second command, we are using the output file from our first command as our second input file to help create the gif using the paletteuse filter.

Show the differences between two input files

ffmpeg -i input1.mkv -i input2.mkv -filter_complex "blend=all_mode=difference" differences.mkv

We are creating an output file that blends the video streams into each other using the blend filter to display the difference between the streams.

Conclusion

Hopefully this gives us a basic idea of what FFmpeg is and what its ffmpeg tool can do. FFmpeg can be both useful and daunting given its scope and scale. Our community encourages ongoing learning of these tools. Questions are always welcomed as well.

Next, we will walk through how to set up FFmpeg and related tools on our machine to begin encoding for ourselves.