Re: Compressed Audio Playback/Capture through ALSA framework

[Patrick Lai <plai@codeaurora.org>]

On 3/15/2011 1:40 PM, Eliot Blennerhassett wrote:
> On 16/03/11 07:31, Patrick Lai wrote:
>> Hi,
>>
>> Is there a precedent for playback/capture compressed audio stream
>> through ALSA playback/capture interface if underlying hardware supports
>> decoder + sink&  encoder + source capabilities?
>
> No.  (Apart from AC3 passthrough to spdif output)

I presume you are referring to IEC958 format. Are there ASoC drivers 
that support IEC958 format already? Why is AC3 passthrough acceptable
but not other compressed audio format?

> ALSA might be extended to cope with compressed audio with fixed frame
> size and bitrate,

but dealing with any VBR encoding is likely to be even
> more problematic.

> This is because alsa assumes a fixed relationship between samplerate and
> data rate, and also assumes that samples fit in an integer number of bytes.
>
> AFAIK dealing with hardware enc/dec has been done using gstreamer plugins.
> E.g. http://www.lca2010.org.nz/slides/50315.pdf
>
>
> Given that audioscience makes cards that support mp3 encode/decode as
> well as pcm, I'd like it if alsa *did* support compressed audio...
>
>> Which source file can I find an example?
>>
>> Thanks
>> Patrick
>>
>
> regards
>


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