I've been aware of this feature for over decade, but I can't recall whether I've ever tested it.
You are probably already aware of this, but it would only be useful for a digital output, not any analog outputs. Since you mentioned SPDIF, you're probably on the same page. You are correct that the encoded Dolby stream has the *bandwidth* of a 2.0 signal - e.g. 16/44k1 CD audio over a 24/44k1 digital audio transport, or 16/48k DAT audio over a 24/48k digital audio transport. The receiver takes in this encoded Dolby stream and might extract 2.1 or 5.1 or any other number of surround channels, according to the data. I assume that DTS encoded streams would work equally well. Although CoreAudio cannot decode DTS (to my knowledge), it can certainly pass on the encoded bits for external hardware to decode. In either case (Dolby or DTS), I assume that you wouldn't touch the number of channels. Since I've never tested this, I haven't witnessed the audio stream format in action. I don't even know what macOS applications can play Dolby encoded audio, so that might be a starting point. I also assume that the application playing Dolby encoded audio would need to set CoreAudio "hog mode" to prevent other applications from mixing in PCM audio, but that's probably not a concern of your driver. Your driver will receive the same amount of data as a 2.0 PCM stream, and will pass the data on to/from the SPDIF hardware. Speaking of which, I don't know whether you'll get the typical 32-bit float that CoreAudio uses, or if the stream format would be forced into integer mode. If float, your driver cannot make any mistakes converting from float to int, or else the encoding will be corrupted. As for Dolby Atmos, if you have external hardware that decodes Atmos, then I assume macOS would not have any effect on support for the format. Yes, this is exciting stuff. I've worked with surround quite a bit. I've authored DTS discs that play in external hardware. However, I've never been able to link my computer audio directly to my surround receiver/decoder because I never quite found the applications that support surround (even though CoreAudio supports it, many applications do not). Brian Willoughby On Jan 19, 2023, at 4:02 PM, Gagan Sidhu wrote: > this is too sick indeed > (https://lists.apple.com/archives/coreaudio-api/2013/Mar/msg00128.html) > > i have to talk to clemens about whether this is worth the effort in addition > to the natural PCM formats he’s specified. > > if this format is easy to deal with, then it’s gonna take this card to the > next level for real. > > i have some questions about this: knowing that SPDIF’s physical properties > are 2.1, do we even touch the number of channels? > > i assume we leave it as a two channel signal that is passed in this format, > and expect our amp to do the rest? > > anyone know how the dolby atmos wrinkle (added in CRAPALINA [10.15] > https://developer.dolby.com/platforms/apple/macos/os-support/) manifests? > -maybe the kIOAudioStreamSampleFormat1937AC3 somehow adds dolby or > something? > > this is kind of exciting. > > Thanks, > Gagan > > On Mar 19 2013, at 7:23, Jeff Moore <email@fuckinghiddenWTFlol> wrote: >> Yes. The data that comes down to the driver will be AC-3. Note that because >> the format is not mixable, there are parts of the IOAudio family's data >> transfer pipe that get skipped, particularly the mixing parts. >> -- >> Jeff Moore >> Core Audio >> Apple >> >> On Mar 19, 2013, at 5:49 PM, Phil Montoya <email@hidden> wrote: >>> Very nice! So if we publish an IOAudioStream format with the Dolby sample >>> format, what will we get in our clip call? Will it be Dolby encoded audio >>> data? I ask this because PCM formats arrive as floats so we do have to do >>> some conversion. I'm wondering what type of conversion (if any) is needed >>> for Dolby? >>> >>> -Phil >>> >>> On Mar 19, 2013, at 5:29 PM, Jeff Moore <email@hidden> wrote: >>>> Dolby is the format that is called kIOAudioStreamSampleFormat1937AC3 in >>>> the header. The format is a bitstream that would be sent over a SPDIF >>>> cable. >>>> -- >>>> Jeff Moore >>>> Core Audio >>>> Apple >>>> >>>> On Mar 19, 2013, at 5:24 PM, Phil Montoya <email@hidden> wrote: >>>>> I'm wondering if it is possible to support Dolby encoded audio in a core >>>>> audio driver? I don't see Dolby as a choice for the sampleFormat in the >>>>> IOAudioStreamFormat. _______________________________________________ Do not post admin requests to the list. They will be ignored. Coreaudio-api mailing list ([email protected]) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/coreaudio-api/archive%40mail-archive.com This email sent to [email protected]
