[alsa-devel] S/PDIF and track markers (echo3g)

[Anssi Hannula]

17.06.2016, 16:29, Mark Hills kirjoitti:
> Hi,

Hi,

> Is there any provision in ALSA (either within the kernel or libasound) for 
> extracting track marker information from S/PDIF?

I don't know what track marker data looks like, but see below.

> I have a large number of MiniDisc recordings to preserve as FLAC format.
> 
> Losing track markers would be a huge inconvenience, though I don't care 
> for the rest of the metadata (track names etc..)
> 
> There's enough recordings to be worth developing specific software for the 
> archival if it can access this information.
> 
> I don't really know which path is likely to be successful:
> 
> * An ALSA API to access the information; though I can't see anything
>   specific to track markers
> 
> * Whether a timecode could be used to detect track change; but I can't see 
>   any in /proc/asound/Layla3G/status
> 
> * Does ALSA provide access to raw AES streams, so I could decode it in 
>   userland? I'm un-sure if this relates to hardware AC3 decoding.

ALSA does provide access to the raw stream with drivers that support
that. You'll need to record with IEC958_SUBFRAME_LE or
IEC958_SUBFRAME_BE sample formats.

> * Maybe this sort of status is only available to the firmware of the 
>   interface and never makes it to userland (in my case, echo3g); though I 
>   can see some constants relating to 'non audio' S/PDIF.

Unfortunately the echo3g driver doesn't seem to support
IEC958_SUBFRAME_* sample formats.

The HDA driver, used for most mainboard/laptop integrated audio, does
support that format if the hardware is capable. I'm not sure if the
hardware commonly supports that format or not, though.

> The hardware I have here is Echo Layla 3G (snd-echo3g) and a Pioneer 
> MJ-D707 MiniDisc recorder.
> 
> Any advice appreciated -- many thanks.
> 


-- 
Anssi Hannula