Re: [edk2-devel] VirtIO Sound Driver (GSoC 2021)

["Michael Brown" <mcb30@ipxe.org>]

On 16/04/2021 00:42, Ethin Probst wrote:
> Forcing a particular channel mapping, sample rate and sample format on
> everyone would complicate application code. From an application point
> of view, one would, with that type of protocol, need to do the
> following:
> 1) Load an audio file in any audio file format from any storage mechanism.
> 2) Decode the audio file format to extract the samples and audio metadata.
> 3) Resample the (now decoded) audio samples and convert (quantize) the
> audio samples into signed 16-bit PCM audio.
> 4) forward the samples onto the EFI audio protocol.

You have made an incorrect assumption that there exists a requirement to 
be able to play audio files in arbitrary formats.  This requirement does 
not exist.

With a protocol-mandated fixed baseline set of audio parameters (sample 
rate etc), what would happen in practice is that the audio files would 
be encoded in that format at *build* time, using tools entirely external 
to UEFI.  The application code is then trivially simple: it just does 
"load blob, pass blob to audio protocol".

> typedef struct EFI_SIMPLE_AUDIO_PROTOCOL {
>    EFI_SIMPLE_AUDIO_PROTOCOL_RESET Reset;
>    EFI_SIMPLE_AUDIO_PROTOCOL_START Start;
>    EFI_SIMPLE_AUDIO_PROTOCOL_STOP Stop;
> } EFI_SIMPLE_AUDIO_PROTOCOL;

This is now starting to look like something that belongs in boot-time 
firmware.  :)

Michael