How to get 4 Chanel Audio for ambisonic sound

Help/How To
1

I am mostly using shotcut to preform “nice” merges of video files with FTB transitions, title screens, etc. The source is 8k with 4 Chanel audio, this allows for the audio to track the user.

I was wondering how to make shotcut export with 4 channels, or should I export with 6 and toss the extra 2? (and if so, how do I toss the extra channels?)

I’m planning on adding the metadata separately, so that’s not a problem, I just want to copy the audio tracks after the audio filters. (Just fades to/from silence.)

2

Shotcut export supports mono (1), stereo (2) and 5.1 surround (6) for export. What is the channel layout/configuration for your 4 channels. Are they completely independent channels?

3

I’m presuming it’s based off the specs found in GitHub - google/spatial-media: Specifications and tools for 360º video and spatial audio.

Although this seems to be a better explanation of how the channels work: Ambisonics Explained: A Guide for Sound Engineers - Waves Audio

  • W is an omni-directional polar pattern, containing all sounds in the sphere, coming from all directions at equal gain and phase.
  • X is a figure-8 bi-directional polar pattern pointing forward.
  • Y is a figure-8 bi-directional polar pattern pointing to the left.
  • Z is a figure-8 bi-directional polar pattern pointing up
4

4 channel Ambisonic audio is a common use case now with 360 video cameras. GoPro MAX shoots with this option. We should add 4 channels sometime, but for now use 6 channels. Then, when you are done you can process the file with ffmpeg while using -codec:v copy to keep the video. Reducing audio channels is not super simple, but there are some tips here or elsewhere in a web search:
https://trac.ffmpeg.org/wiki/AudioChannelManipulation

5

Dan’s suggestion is probably the best. You could also try to get 4 channel out by adding these two options to the “Other” tab in the advanced section of the export panel:

channels=4
channel_layout=independent

I have not tested this.

6

I tested this, and it works. In Audacity compared waveforms of an ambisonic input and a WAV export with the above options, and all the channels look the same.

7

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