Messages in this thread | | | Date | Wed, 29 Oct 2014 10:06:19 -0500 | From | Pierre-Louis Bossart <> | Subject | Re: [alsa-devel] [PATCH 00/11] Add AXD Audio Processing IP driver |
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On 10/28/14, 8:18 AM, Qais Yousef wrote: > On 10/28/2014 11:55 AM, Clemens Ladisch wrote: >> Qais Yousef wrote: >>> AXD Audio Processing IP performs audio decoding, encoding, mixing, >>> equalisation, >>> synchronisation and playback. >> What exactly do you mean with "synchronisation" and "playback"? > > Synchronisation refers to accurate audio playout relative to a master > clock source including compensation of drift between the master clock > source and the playout clock of the audio hardware. Hence allowing > synchronised audio playout across multiple independent devices. > > Playback simple refers to the fact that AXD is capable of managing audio > playout hardware like I2S and SPDIF interfaces. > > >>> It doesn't fit in alsa subsystem but I Cced them to confirm. >> ... because those two words sound like something that a sound card >> could do. > > The problem mainly stems from the fact that we take a variety of > compressed audio as input and we could perform audio encoding. The > problem with the compressed audio is that the range of decoders and > configuration supported in alsa is limited and there's no support for > taking raw pcm and producing compressed output. I'm not an expert on > alsa but when I looked it looked like there's more infra structure > required. > > The following not supported points from > Documentation/sound/alsa/compress_offload.txt affect us: > > - Volume control/routing is not handled by this API. Devices exposing a > compressed data interface will be considered as regular ALSA devices; > volume changes and routing information will be provided with regular > ALSA kcontrols. > > - Embedded audio effects. Such effects should be enabled in the same > manner, no matter if the input was PCM or compressed. > > - Encoding/decoding acceleration is not supported as mentioned > above. It is possible to route the output of a decoder to a capture > stream, or even implement transcoding capabilities. This routing > would be enabled with ALSA kcontrols.
Volume control, effects and routing aren't supported directly with the snd_pcm streaming interface either. we didn't add these features either in the compressed API since they could be enabled through existing means (kcontrols and routing).
> > > >>> I added it to drivers/char as this is the best location I could think >>> of at the >>> moment. >> drivers/misc? > > Yeah could do if there's consensus. > > Thanks, > Qais > >> >> Regards, >> Clemens > > _______________________________________________ > Alsa-devel mailing list > Alsa-devel@alsa-project.org > http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
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