Re: [PATCH 04/23] ASoC: soc-compress: Implement trigger FE-BE sequencing as with normal PCMs

["Péter Ujfalusi" <peter.ujfalusi@linux.intel.com>]

On 08/09/2026 17:54, Pierre-Louis Bossart wrote:
> 
>> I see, the issue is that I cannot find any way to give the metadata to
>> the decoder module, it is a black box to us.
> 
> The metadata is typically handled *outside* of the decoder library by a
> memcpy-based wrapper or modulo pointers.
> 
> For example due to the filterbank, the decoder will generate N zero
> samples in the first frame. If you know the value of N thanks to the
> METADATA ioctl, you can discard the first N samples in the wrapper.
> 
> Likewise at the end of the track the wrapper can skip the last M samples
> which were padded to make the initial soundtrack a multiple of the frame
> size (e.g. 1152 for MP3). the value M is the encoder padding.

I got this part, but I have no idea how the wrapper could know this.
It can be only _after_ the decoder to do the fade out/in/mixing, but so
far I have not seen any way to actually pin-point the exact time.
And not just exact time, but T minus something to T plus something.

>> Also I'm not sure how the fw could get any idea where one
>> flac/vorbis/aac/mp3 ends and where it starts, the black box does not
>> seam to be able to detect this or if it does, it will not emit this
>> information to outside.
> I must admit I don't fully remember the details on the start/end
> position. IIRC this isn't strictly required for elementary streams such
> as MP3 or AAC ADTS, you could cat the streams together and that'd be
> just fine. you would have a slightly different transition by blending
> the two streams in a common filterbank history buffer but that'd be
> nearly impossible to detect...

and there is still the monitoring of the progress of let's say 6th track
in the stream.

I was planning to revisit this sooner than later when I have a moment of
'free' time, but for this initial series, it is not promised and should
not work at all.

> But for streams with a header such as WMA not sure how this might work,
> I think you do need to know the buffer position, reset the decoder and
> restart from that position.

Luckily no one has such files anymore ;)

-- 
Péter