Enabling Ambisonic Encoding

[MandyJCho]

Hi there,

I was following this thread about the --enable-ambisonic flag. Are there instructions to enable the ambisonic API with the opusenc cli? The documentation for 1.3 mentions support for channel mapping families 2 and 3, but it's unclear where I can configure this.

Right now the layout is being set to quad rather than 'ambisonic 1'

Input #0, ogg, from '.\ambisonic_opusenc.opus':
  Duration: 00:00:29.04, start: 0.000000, bitrate: 185 kb/s
  Stream #0:0: Audio: opus, 48000 Hz, quad, fltp
    Metadata:
      ENCODER         : opusenc from opus-tools 0.2-3-gf5f571b

Here's an output using ffmpeg to transcode audio:

Input #0, ogg, from '.\ambisonic_ffmpeg_2.opus':
  Duration: 00:00:29.04, start: 0.000000, bitrate: 113 kb/s
  Stream #0:0: Audio: opus, 48000 Hz, ambisonic 1, fltp
    Metadata:
      encoder         : Lavc59.51.100 libopus

[Artoria2e5]

Could be --channels ambix per

opus-tools/man/opusenc.1

Line 317 in ecd50e5

The "ambix" option indicates that the input is ambisonics using ACN channel

family 2 (matrix) is the default and I am not seeing any place to change it. well, multi-mono is probably much worse anyways.

opus-tools/src/opusenc.c

Lines 901 to 906 in ecd50e5

	if (inopt.channels_format==CHANNELS_FORMAT_AMBIX) {
	validate_ambisonics_channel_count(chan);
	/*Use channel mapping 3 for orders {1, 2, 3} with 4 to 18 channels
	(including the non-diegetic stereo track). For other orders with no
	demixing matrices currently available, use channel mapping 2.*/
	mapping_family=(chan>=4&&chan<=18)?3:2;