search for: ambix

...to experiment with ambisonics, but > doesn't seem like the best solution for adding official support for > ambisonics in opus-tools, which is intended for use by end users. > Ideally no additional options would be needed and opusenc would be > able to identify a WAV file containing Ambix-compatible ambisonic > channels and by default convert such a file to a compressed ambisonic > output file in the format described by draft-ietf-codec-ambisonics. > However it appears that there is unfortunately no agreed upon metadata > to identify such WAV files, and the user will nee...

Friendly ping for the opus-tools patch... ---------- Forwarded message --------- From: Drew Allen <bitllama at google.com> Date: Mon, Mar 19, 2018 at 2:53 PM Subject: Re: [PATCH] Support for Ambisonics To: opus at xiph.org <opus at xiph.org> On Mon, Mar 19, 2018 at 11:52 AM Drew Allen <bitllama at google.com> wrote: > Hello all, > > Sorry for the delay (got really

...kay for a quick hack to experiment with ambisonics, but doesn't seem like the best solution for adding official support for ambisonics in opus-tools, which is intended for use by end users. Ideally no additional options would be needed and opusenc would be able to identify a WAV file containing Ambix-compatible ambisonic channels and by default convert such a file to a compressed ambisonic output file in the format described by draft-ietf-codec-ambisonics. However it appears that there is unfortunately no agreed upon metadata to identify such WAV files, and the user will need a way to manually...

...ambisonics, as I'm not a codec expert. So I think that the easiest (and most important for now) is to disable channel coupling and define the metadata. The allowed number of channels should not be restrained to a list like 1,4,9,16,etc, because ambisonics can support mixed-order schemes. The Ambix format was adopted by Google, but it's a new format; the FuMa format is widely used and could easily be supported as well. https://en.wikipedia.org/wiki/Ambisonic_data_exchange_formats Down-mixing to stereo is a sort of ambisonic decoding; it is simple and could be included in the Opus decode...

...TA[ sqrt((2 - delta(m)) * ((l - m)! / (l + m)!)), ]]></artwork> </figure> <t> where delta(0) = 1 and delta(m) = 0 otherwise. </t> <t> The interpretation of the ambisonics signal as well as the channel order and normalization are described in <xref target="ambix"/>. </t> </section> <section anchor="downmixing" title="Downmixing"> <t> Implementations MAY use the matrix in Figure <xref target="stereo_downmix_matrix" format="counter"/> to implement downmixing from multichannel fi...

...nnels: (1 + l)^2 for l = 0...14" > > Minor nit: unless the use of "l" is standard for talking about > ambisonics, I would suggest using "k" instead, since "l" is easy to > confuse with "1". Actually "n" is common and is used in the [ambix] reference, so I switched to that and changed the language here to be consistent with [ambix]. > Section 3.1: If it's not too complicated, can you explain how the "m" > index is derived? I added equations to derive n and m from channel index. I've attached updated versions...

I compiled the latest (git master) of opus, libopusenc, opusfile and opus-tools: $ opusenc --version opusenc opus-tools 0.2-8-g4976421 (using libopus 1.3.1-4-gad8fe90d) I tried to encode a 3rd order Ambisonics wav file with the standard Ambix (ACN-SN3D) format; opusinfo is reporting : Streams: 16, Coupled: 0     Channel Mapping Family: 255 Map: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15] How to encode the file so that the Mapping Family is 3, as suggested here ? : https://people.xiph.org/~jm/opus/opus-1.3/ Marc

...t;output channels". > > > It's also probably a good idea to explicitly say that you use the same > > channel mapping table format as channel mapping families 1 and 255. At > > least, I'm assuming you do. I'm also assuming you don't plan to support > > Ambix's "extended format" with its adaptor matrix. > Thanks, I reworded to > > "This channel mapping uses the same channel mapping table format used > by channel mapping families 1 and 255. Each output channel is > assigned..." > > You are correct, I think it...

...ng, ie WY_X instead of WYZX for horizontal only. Restricting channel counts to (l + 1)^2 would allow us to include rules for "hemispherical" ambisonics. These are sets of ambisonic components with different shapes more suitable for encoding certain content. An example is described in the ambix paper [1]. I need to talk with some of the VR people here to figure out whether these hemispherical encodings are likely to be used by anyone (at Google or elsewhere). I could not find a commonly used set of basis functions like the spherical harmonics used in ordinary ambisonics, so we may want to...

...me you mean "output channels" here, and should say so. It's also probably a good idea to explicitly say that you use the same channel mapping table format as channel mapping families 1 and 255. At least, I'm assuming you do. I'm also assuming you don't plan to support Ambix's "extended format" with its adaptor matrix.

...gt; I compiled the latest (git master) of opus, libopusenc, opusfile and > opus-tools: > > $ opusenc --version > opusenc opus-tools 0.2-8-g4976421 (using libopus 1.3.1-4-gad8fe90d) > > I tried to encode a 3rd order Ambisonics wav file with the standard > Ambix (ACN-SN3D) format; opusinfo is reporting : > > Streams: 16, Coupled: 0 >     Channel Mapping Family: 255 Map: [0, 1, 2, 3, 4, 5, 6, 7, 8, > 9, 10, > 11, 12, 13, 14, 15] > > How to encode the file so that the Mapping Family is 3, as suggested > here ?...

...t; Channel mapping family: 2 I am trying to encode 6 Channels as Opus to an .opus and .webm file. Until now, YouTube and Chrome Browser cannot playback the results correctly. VLC is not playing anything. Using this MOV container and PCM works. I am using the following ffmpeg command: ffmpeg -i ambix_6ch_withHLS.wav -c:a libopus -b:a 768k -mapping_family 2 -y ambix.opus The opusenc.exe binary does not mention a command line argument for channel mapping. In this mailing list archive, Emily Bowman mentioned 19 December 2019, that Ambisonics is an API-only feature. Is this still correct? Here&...

...add them without > breaking existing implementations. I see, thanks for the explanation. I'm not familiar enough with Ogg, as I was using AAC with the m4a contrainer for my "ambisonics on the web" experiments. I'm now confident that Opus will be largely adopted. > > The Ambix format was adopted by Google, but it's a new format; > > the FuMa format is widely used and could easily be supported as > > well. https://en.wikipedia.org/wiki/Ambisonic_data_exchange_formats > > Although FuMa conventions are commonly used, the ambix conventions of > ACN...

...ose channels which are not included ({2,3}, {3}, {5,6,7,8} in this example). We reserved actual channel number "C" == 2,3,5,etc so that if mixed order schemes with different basis functions become common in the future, we could add them without breaking existing implementations. > The Ambix format was adopted by Google, but it's a new format; > the FuMa format is widely used and could easily be supported as well. > https://en.wikipedia.org/wiki/Ambisonic_data_exchange_formats Although FuMa conventions are commonly used, the ambix conventions of ACN channel ordering and SN3D...

...I compiled the latest (git master) of opus, libopusenc, opusfile and >> opus-tools: >> >> $ opusenc --version >> opusenc opus-tools 0.2-8-g4976421 (using libopus 1.3.1-4-gad8fe90d) >> >> I tried to encode a 3rd order Ambisonics wav file with the standard >> Ambix (ACN-SN3D) format; opusinfo is reporting : >> >> Streams: 16, Coupled: 0 >> Channel Mapping Family: 255 Map: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, >> 11, 12, 13, 14, 15] >> >> How to encode the file so that the Mapping Family is 3, as suggested >> here ? :...

Hi Michael, On 04/25/2016 05:32 AM, Michael Graczyk wrote: > Channel Mapping Family 2 > > Allowed numbers of channels: (1 + l)^2 for l = 1...15. > > Explicitly 1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144, 169, 196, > 225. Ambisonics from first to fifteenth order. Would it make sense to allow an arbitrary number of channels and just "truncate" the list of

...ion (SN3D). In SN3D, the ambisonic component of degree n and index m is normalized according to sqrt((2 - delta(m)) * ((l - m)! / (l + m)!)), where delta(0) = 1 and delta(m) = 0 otherwise. ------ I chose ACN order and SN3D normalization because these seem to be the most common, and are used by the Ambix format and by Google's spatial audio RFC: https://github.com/google/spatial-media/blob/master/docs/spatial-audio-rfc.md I have a couple of questions about the definition and language. 1. Should I be more explicit about what "ambisonics" is, what normalization is, and what each chann...

...ation (SN3D). In SN3D, the spherical harmonic of degree n and index m is normalized according to sqrt((2 - delta(m)) * ((l - m)! / (l + m)!)), where delta(0) = 1 and delta(m) = 0 otherwise. The interpretation of the ambisonics signal as well as the channel order and normalization are described in [ambix]. ---- and in section 5.1.1.5 ----- Implementations MAY use the matrix in Figures ? to implement downmixing from multichannel files using Channel Mapping Family 2 (Section 5.1.1.?), which are known to give acceptable results for stereo. / \ / \ / W \ | L | | 0...

...ed channels here to "output channels". > It's also probably a good idea to explicitly say that you use the same > channel mapping table format as channel mapping families 1 and 255. At > least, I'm assuming you do. I'm also assuming you don't plan to support > Ambix's "extended format" with its adaptor matrix. Thanks, I reworded to "This channel mapping uses the same channel mapping table format used by channel mapping families 1 and 255. Each output channel is assigned..." You are correct, I think it is not worth the complexity to su...

...cklava.net> wrote: > I compiled the latest (git master) of opus, libopusenc, opusfile and > opus-tools: > > $ opusenc --version > opusenc opus-tools 0.2-8-g4976421 (using libopus 1.3.1-4-gad8fe90d) > > I tried to encode a 3rd order Ambisonics wav file with the standard > Ambix (ACN-SN3D) format; opusinfo is reporting : > > Streams: 16, Coupled: 0 > Channel Mapping Family: 255 Map: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, > 11, 12, 13, 14, 15] > > How to encode the file so that the Mapping Family is 3, as suggested > here ? : https://people.xiph.org/~jm...