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2024-09-24 Video Production

Understanding Video and Audio Bitrates for Encoding

By O. Wolfson

This guide will help you understand bitrate standards for different video and audio formats, including MP4, MKV, WebM, and more. We’ll start with generalized bitrate recommendations and then dive into more specific guidelines based on formats and codecs.

Table of Contents

General Bitrate Guidelines

What is Bitrate?

Bitrate refers to the amount of data processed over a given amount of time during video or audio playback. It is usually measured in megabits per second (Mbps) for video and kilobits per second (kbps) for audio. Higher bitrates generally result in better quality but larger file sizes.

Video Bitrate Recommendations

General Recommendations for Different Resolutions:

  • 1080p (1920x1080):
    • Low-quality: 3-6 Mbps
    • Standard-quality: 8-10 Mbps
    • High-quality: 10-20 Mbps
  • 4K (3840x2160):
    • Low-quality: 20-35 Mbps
    • Standard-quality: 35-45 Mbps
    • High-quality: 50-100 Mbps
  • 720p (1280x720):
    • Low-quality: 1.5-3 Mbps
    • Standard-quality: 3-5 Mbps
    • High-quality: 5-10 Mbps
  • 480p (SD, 854x480):
    • Low-quality: 0.5-1 Mbps
    • Standard-quality: 1-2.5 Mbps
    • High-quality: 2.5-5 Mbps

Factors Affecting Video Bitrate:

  1. Resolution: Higher resolution videos require more bitrate.
  2. Frame Rate: Higher frame rates require more bitrate (e.g., 60 fps vs. 30 fps).
  3. Content Complexity: Fast action or high-detail scenes need higher bitrates to avoid artifacts.
  4. Use Case: Streaming platforms use lower bitrates to accommodate bandwidth, whereas offline playback (e.g., Blu-ray) uses higher bitrates.

Audio Bitrate Recommendations

General Audio Bitrate Guidelines:

  • AAC (Advanced Audio Coding):

    • Stereo (2 channels):
      • Low-quality: 96-128 kbps
      • Standard-quality: 128-192 kbps
      • High-quality: 192-320 kbps
    • 5.1 Surround (6 channels):
      • Standard-quality: 384-448 kbps
      • High-quality: 640-768 kbps

  • MP3:

    • Low-quality: 96-128 kbps
    • Standard-quality: 128-192 kbps
    • High-quality: 192-320 kbps

  • FLAC (Lossless): Typically ranges between 500-1200 kbps depending on the complexity of the audio.

Codec Efficiency and Bitrate Considerations

Different codecs have varying efficiency levels. Efficient codecs can produce higher quality at lower bitrates.

  • H.264 (AVC): The most common codec, offering good balance between quality and size. Bitrate suggestions here mostly apply to H.264 encoding.
  • H.265 (HEVC): 50% more efficient than H.264. You can reduce the bitrate by half for the same quality.
  • VP9 (WebM): Similar in efficiency to H.265, often used by YouTube for 4K video.
  • AAC: Efficient for audio compression, widely supported for both stereo and surround sound.
  • Opus: More efficient than AAC for audio, especially for streaming.

Bitrate Guidelines for Specific Formats

Let’s dive into more specific bitrate recommendations based on common video formats. These values consider the codec and format used for encoding.

MP4 / MOV (H.264 + AAC)

For MP4 or MOV files using H.264 for video and AAC for audio:

  • 1080p video bitrate: 8-10 Mbps for good quality, up to 20 Mbps for high-quality.
  • 4K video bitrate: 35-50 Mbps for good quality.
  • Audio bitrate (stereo): 128-192 kbps for standard quality, 320 kbps for high quality.
  • Audio bitrate (5.1 surround): 384-640 kbps.

MKV (H.264 / H.265 + AAC / FLAC)

MKV files often use either H.264 or H.265 for video and AAC or FLAC for audio:

  • H.265: Reduce video bitrate by 50% compared to H.264. For example, 10 Mbps H.264 can be 5 Mbps H.265.
  • FLAC: As a lossless audio codec, expect higher bitrates between 500-1200 kbps, depending on the complexity.

WebM (VP9 + Opus)

WebM typically uses VP9 for video and Opus for audio:

  • Video bitrate: You can reduce video bitrate by about 30-50% compared to H.264.
  • Audio bitrate: Opus is more efficient than AAC, so you can use lower bitrates (e.g., 96-128 kbps for stereo).

AVI (DivX / Xvid)

AVI is an older format and typically uses DivX or Xvid for video:

  • Video bitrate: Increase the bitrate by 20-30% compared to H.264 to achieve similar quality.
  • Audio bitrate: MP3 is commonly used, so follow MP3 guidelines for audio (128-320 kbps for stereo).

Conclusion

Bitrate plays a key role in the quality and size of your video and audio files. While the guidelines in this article serve as a starting point, you should adjust based on the specific requirements of your project, format, and use case. For modern codecs like H.265 or VP9, you can lower bitrates while maintaining high quality. For older formats like AVI, higher bitrates may be needed to achieve acceptable quality.

By understanding how bitrate, resolution, and codecs interact, you can optimize your media files for quality, efficiency, or size, depending on your goals.

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