How to: Understand FFmpeg flags

FFmpeg's flags can be confusing if you aren't familiar with them, and sometimes even if you are familiar! Let's take a look at some of them and see what they mean.

a month ago   •   1 min read

By Tom O'Brien
Table of contents
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Flags, also known as options or switches, are command-line parameters used to modify the behavior of a command or program. Flags are typically preceded by a hyphen (-) or a double hyphen (--), and they provide additional instructions or specify options when executing a command.

FFmpeg is a powerful tool for processing audio and video files, but its commands can appear complex at first glance. Let's break down the process of understanding an FFmpeg command into simpler steps:

Identify the basic function

Most FFmpeg commands start with an action verb, like ffmpeg -i input.mp4 output.avi. Here, ffmpeg is the program name, -i specifies the input file (input.mp4), and output.avi is the output filename.

Break down the options

The -i option is followed by various flags and parameters that control FFmpeg's behavior. These can be categorized into:

  • Input options: These specify properties of the input file, like -i input.mp4 which tells FFmpeg to use "input.mp4" as the source.
  • Output options: These control the output file's format, quality, and other aspects. For example, .avi in the command specifies the output format as AVI.
  • Codec options: Codecs are used for encoding and decoding audio/video data. FFmpeg can use different codecs depending on your needs.

Understand common options

Some frequently used options include:

  • -c:v codec: This specifies the video codec to use for encoding/decoding (e.g., -c:v libx264 for H.264 video).
  • -c:a codec: Similar to -c:v but for audio codecs (e.g., -c:a libmp3lame for MP3 audio).
  • -b:v bitrate: Sets the video bitrate, which affects video quality and file size (e.g., -b:v 5M for 5 Mbps bitrate).
  • -ar samplerate: Sets the audio sample rate, which affects audio quality (e.g., -ar 44100 for 44.1 kHz sample rate).

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