On Wed, Aug 14, 2024 at 5:40 PM Pierre-Louis Bossart pierre-louis.bossart@linux.intel.com wrote:
Yes, to go further, I think we can use SND_AUDIOCODEC_PCM, then the SRC type will be dropped.
sounds good.
But my understanding of the control means the .set_metadata() API, right? As I said, the output rate, output format, and ratio modifier are applied to the instances of ASRC, which is the snd_compr_stream in driver. so only the .set_metadata() API can be used for these purposes.
Humm, this is more controversial.
The term 'metadata' really referred to known information present in headers or additional ID3 tags and not in the compressed file itself. The .set_metadata was assumed to be called ONCE before decoding.
But here you have a need to update the ratio modifier on a regular basis to compensate for the drift. This isn't what this specific callback was designed for. We could change and allow this callback to be used multiple times, but then this could create problems for existing implementations which cannot deal with modified metadata on the fly.
.set_metadata can be called multi times now, no need to change currently.
And then there's the problem of defining a 'key' for the metadata. the definition of the key is a u32, so there's plenty of space for different implementations, but a collision is possible. We'd need an agreement on how to allocate keys to different solutions without changing the header file for every implementation.
Can we define a private space for each case? For example the key larger than 0x80000000 is private, each driver can define it by themself?
It sounds like we'd need a 'runtime params' callback - unless there's a better trick to tie the control and compress layers?