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Changing Audio Bit Rate

Adjust the audio bit rate of a video or audio file using FFmpeg, allowing for modifications in audio quality and file size.

VideoAlchemy Compose File

version: 1  # Schema version of viddo-compose

generate_path: "./generated"  # Directory of log and command files

tasks:
  - name: Changing Audio Bit Rate
    command: ffmpeg
    inputs:
      - id: input_3
        source: 'input.mp4'
    outputs:
      - id: output_3
        overwrite: true
        source: 'output.mp4'
    codecs:
      - constant_bitrate:
          audio: 128k

Command

ffmpeg -i input.mp4 -b:a 128k output.mp4

Parameters

  • -i input.mp4: Specifies the input file. This can be either a video or an audio file. Replace input.mp4 with the path to your source file.
  • -b:a 128k: Sets the audio bit rate to 128 kbps. Adjust 128k to your desired audio bit rate.

Possible Errors

  • File not found: Occurs if FFmpeg cannot locate the input file. Make sure the path to the file is correct.
  • Invalid bit rate value: Happens if the specified audio bit rate is not recognized. Ensure the bit rate value is specified correctly, using k for kbps.
  • Permission denied: Arises if FFmpeg does not have the required permissions to read the input file or write to the output file. Check that the files and directories have the correct permissions.

GPU Acceleration Command

Changing the audio bit rate is a CPU-bound process, as it involves encoding audio streams rather than video. Therefore, there's no direct application of GPU acceleration for altering audio bit rates with FFmpeg. The focus is on the audio codec's performance, which is managed by the CPU:

ffmpeg -i input.mp4 -c:a aac -b:a 128k output.mp4

Additional Information

  • Audio Quality and File Size: The audio bit rate directly impacts the quality and size of the audio track. Higher bit rates mean better quality but larger file sizes, while lower bit rates can significantly reduce file size at the cost of audio quality.
  • Choosing the Right Codec: Along with bit rate, the audio codec (e.g., AAC, MP3) plays a crucial role in determining the quality of the output audio. Some codecs are more efficient than others, offering better quality at lower bit rates.
  • Compatibility: Ensure the selected audio codec and bit rate are compatible with the intended playback systems or platforms. This is especially important when optimizing for web streaming or devices with limited storage.
  • Re-encoding: Changing the audio bit rate requires re-encoding the audio track. Consider the trade-off between file size and audio quality before deciding on the bit rate.