Audio GIFs (.a.gif)

"Sounds Like a Bad Idea."

TL;DR: An Audio GIF stores audio inside a standards compliant Animated GIF image.

• Unlike other approaches there is no need for a separate audio or video file.
• Use Save As... on the Animated GIF image file and the audio comes along for the ride.
• Share the Animated GIF file and you've shared the audio!

Samples

• View & hear the "show reel" here: http://audiogif.rancidbacon.com/start

Project repository

• Get tools to create & play your own Audio GIFs: https://github.com/RancidBacon/audiogif

On this page

• How to create an Audio GIF
• Specification for "Audio for GIF" Application Extension
  • Reference Implementation: Encoder
  • Reference Implementation: Player
• FAQ
• References
• Changelog

How to create an Audio GIF

1. Extract the portion of video/audio you want to Audio GIF.

• Requires ffmpeg to be installed first.

This can probably done as a one-liner but this way we can check we've cropped/shortened correctly first.

ffmpeg -ss MM:SS.mm -t SS.mm -i input_video.mp4 -vf "crop=out_w=660:out_h=522:x=250:y=0" -c:a aac -map 0:v -map 0:a my_new.mp4
ffmpeg -ss MM:SS.mm -t SS.mm -i input_video.mp4 -ar 22050 -ac 1 my_new.wav

2. Convert extracted video into an animated GIF.

Note: The gif-encoder.sh script has some hardcoded values you may wish to change.

tools/gif-encoder.sh my_new.mp4 my_new.gif

3. Add audio to your animated GIF to make it an Audio GIF!

• Requires kaitaistructruntime library for Python to be installed first.

tools/gif-audio-add.py my_new.gif my_new.wav

Creates a new file named my_new.a.gif which is the recommend file extension for Audio GIFs.

4. View and hear your new Audio GIF!

You might like to ask your favourite software to add support for the Audio GIF format.

Specification for "Audio for GIF" Application Extension

"Audio for GIF" Application Extension (a.k.a Audio GIF) Specification v0.1

[0x21] Extension Introducer
[0xFF] Extension Label (Standard: "Application Extension")

[0x0B] Block Size (Standard: There are 11 bytes before application data)
[0x41][0x55][0x44][0x49][0x4F][0x47][0x49][0x46] Application Identifier ("AUDIOGIF")
[0x30][0x2E][0x31] Application Authentication Code ("0.1")

[0x01] Block Size (New: Audio Metadata Sub-Block)
[0x01] Audio Data Format (New: 0x00 == Reserved (for WebAudio native format) 0x01 == Determine format by introspection--not implemented assumes .wav))

[Subblock Length][Subblock Data] N * Blocks of Audio (file) data.

[0x00] Empty sub-block marks end of audio data. (Standard)

Reference Implementation: Encoder

See tools/gif-audio-add.py in this repository. The Reference Implementation Encoder builds on the work of https://ffmpeg.org/ and http://kaitai.io/.

Reference Implementation: Player

See thirdparty/gifuct-js in this repository. The Reference Implementation Player is based on https://github.com/matt-way/gifuct-js with Audio GIF functionality added. I chose gifuct-js because it was the easiest to modify JavaScript GIF library that I found.

FAQ

• But why?

  Because sounds like a bad idea. :)

• [TODO]

References

• https://www.w3.org/Graphics/GIF/spec-gif89a.txt
• http://www.matthewflickinger.com/lab/whatsinagif/bits_and_bytes.asp
• http://formats.kaitai.io/gif/index.html
• http://fileformats.archiveteam.org/wiki/GIF

Changelog

• 2019-05-16 Initial v0.1 release.

The Audio GIF is brought to you by http://RancidBacon.com/.