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Understanding FFmpeg Terminology: Codecs, Bitrate, and More

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    Hieu Cao
    Twitter

Introduction

FFmpeg is a powerful tool for multimedia processing, but its terminology can be overwhelming for beginners. This blog will break down some of the most common terms you’ll encounter, such as codecs, bitrate, resolution, and more, to help you better understand and utilize FFmpeg.

Key Terms in FFmpeg

1. Codec

A codec (short for coder-decoder) is a software or hardware tool that compresses and decompresses audio or video data.

  • Common Video Codecs:

    • H.264: Widely used for high-quality video at lower bitrates.
    • VP9: Open-source alternative to H.264.
    • HEVC (H.265): Offers better compression than H.264 but is less compatible.

  • Common Audio Codecs:

    • AAC: Popular for high-quality audio.
    • MP3: Older but widely supported format.

Example in FFmpeg:

Specify the video codec during conversion:

ffmpeg -i input.mp4 -c:v libx264 output.mp4

2. Bitrate

Bitrate refers to the amount of data processed per unit of time, typically measured in kilobits per second (kbps) or megabits per second (Mbps).

  • Higher Bitrate: Better quality but larger file size.
  • Lower Bitrate: Smaller file size but reduced quality.

Example in FFmpeg:

Set a specific bitrate for a video:

ffmpeg -i input.mp4 -b:v 1M output.mp4

3. Resolution

Resolution defines the number of pixels in a video frame, typically represented as width x height (e.g., 1920x1080 for Full HD).

Example in FFmpeg:

Resize a video to 720p:

ffmpeg -i input.mp4 -s 1280x720 output.mp4

4. Frame Rate

Frame rate refers to the number of frames displayed per second, measured in frames per second (fps). Common frame rates include 24 fps, 30 fps, and 60 fps.

Example in FFmpeg:

Change the frame rate of a video:

ffmpeg -i input.mp4 -r 30 output.mp4

5. Container Format

A container format is a file format that stores video, audio, and metadata (e.g., MP4, MKV, AVI).

  • MP4: Highly compatible and efficient.
  • MKV: Supports multiple audio tracks and subtitles.

Example in FFmpeg:

Convert a video to a different container format:

ffmpeg -i input.avi output.mp4

6. Sampling Rate

Sampling rate refers to the number of audio samples per second, measured in hertz (Hz). Common rates include 44.1 kHz and 48 kHz.

Example in FFmpeg:

Change the audio sampling rate:

ffmpeg -i input.mp3 -ar 44100 output.mp3

7. GOP (Group of Pictures)

GOP is a sequence of video frames that includes one keyframe followed by several predicted frames. A smaller GOP size can improve seeking but increases file size.

Example in FFmpeg:

Set the GOP size:

ffmpeg -i input.mp4 -g 50 output.mp4

8. CRF (Constant Rate Factor)

CRF is a quality-based mode for controlling video compression. Lower values produce higher quality and larger file sizes, while higher values reduce quality and file size.

  • Range: 0 (lossless) to 51 (lowest quality).

Example in FFmpeg:

Set the CRF for H.264 encoding:

ffmpeg -i input.mp4 -c:v libx264 -crf 23 output.mp4

Conclusion

Understanding these key terms will help you work more effectively with FFmpeg. Whether you're encoding, compressing, or optimizing multimedia files, knowing how to apply these concepts will make your workflow smoother and more efficient. Start exploring FFmpeg with confidence and unlock its full potential!