[gst-devel] Alsasink rates/channels from gst-inspect versus gstalsa.c

[John Faith]

Tim Müller wrote:
> On Wed, 2007-11-14 at 14:07 -0800, John Faith wrote:
> 
>> On my embedded Power architecture board, I noticed that 'gst-inspect 
>> alsasink' produces:
>>
>>   ...
>>   rate: [ 1, 2147483647 ]
>>   channels: [ 1, 2147483647 ]
>>
>> , whereas gst_alsa_detect_rates() and gst_alsa_detect_channels() in 
>> gst-plugins-base-0.10.12/ext/alsa/gstalsa.c produce minimum rate of 4000 
>> and max channels of 8.
>>
>> Why are the ranges from gst-inspect and printfs in gstalsa.c different?
> 
> gst-inspect prints the so-called 'pad template caps', which comprises
> any format theoretically possible.  gst_alsa_detect_rates() is called
> when the device has been opened, at which point it is possible to query
> the formats the device in question actually supports (which depends on
> things such as the alsa device being used, compare e.g. dmix:0 to hw:0
> to plughw:0, or the device driver or the capabilities of the hardware in
> question).
> 
>  Cheers
>   -Tim


Thanks for your reply.

I started looking at this since "gst-launch audiotestsrc ! audioconvert 
! audioresample ! alsasink" failed with:

...
Setting pipeline to PAUSED ...
Pipeline is PREROLLING ...
Negotiating to 1 channels @ 44100 Hz (format = S16_BE)
ERROR: from element /pipeline0/alsasink0: Could not get/set settings 
from/on resource.
Additional debug info:
gstalsasink.c(438): set_hwparams (): /pipeline0/alsasink0:
Sample format not available for playback: Invalid argument


I thought maybe the right formats/rates were not being returned by 
alsasink and in this case hardcoding the format to S16_LE gets past this 
failure.  I've generated debug output (level=5), but the cause of the 
failure was not obvious to me.

I'm able to play audio with 'aplay', so I assume that the driver is 
working at least to some degree.  Is something else required to make 
alsasink happy?

Thanks!
,
John