---
title: Audio variable bit rate indication
framework: quicktime-file-format
role: article
role_heading: Article
path: quicktime-file-format/audio_variable_bit_rate_indication
---

# Audio variable bit rate indication

## Overview

Overview Feature Values The feature value holds one of the following two values: 0 if the audio is constant bit rate, or 1 if the audio is variable bit rate. Writer Responsibilities A writer of the Audio Variable Bit Rate Indication feature should determine if the audio frames are constant or variable bit rate in nature and record either 0 or 1, respectively. Feature Value Algorithm Consult the audio sample descriptions. If the compressionID field in the sample descriptions is 0 or -1, then the audio is constant bit rate. If the field is -2, then the same algorithm as for video applies: if all the samples have both constant duration and constant size, then the audio is constant bit rate; otherwise it is variable. Reader Responsibilities A reader of this feature code should only expect the values 0 or 1.

## See Also

### Setting features

- [Table of features](quicktime-file-format/table_of_features.md)
- [Maximum video bit rate](quicktime-file-format/maximum_video_bit_rate.md)
- [Average video bit rate](quicktime-file-format/average_video_bit_rate.md)
- [Maximum audio bit rate](quicktime-file-format/maximum_audio_bit_rate.md)
- [Average audio bit rate](quicktime-file-format/average_audio_bit_rate.md)
- [QuickTime video codec type](quicktime-file-format/quicktime_video_codec_type.md)
- [QuickTime audio codec type](quicktime-file-format/quicktime_audio_codec_type.md)
- [MPEG-4 video profile](quicktime-file-format/mpeg-4_video_profile.md)
- [MPEG-4 video codec](quicktime-file-format/mpeg-4_video_codec.md)
- [MPEG-4 video object type](quicktime-file-format/mpeg-4_video_object_type.md)
- [MPEG-4 audio codec](quicktime-file-format/mpeg-4_audio_codec.md)
- [Maximum video size in a movie](quicktime-file-format/maximum_video_size_in_a_movie.md)
- [Maximum video size in a track](quicktime-file-format/maximum_video_size_in_a_track.md)
- [Maximum video frame rate in a single track](quicktime-file-format/maximum_video_frame_rate_in_a_single_track.md)
- [Average video frame rate in a single track](quicktime-file-format/average_video_frame_rate_in_a_single_track.md)