ALSA Compress Offload support

[Qais Yousef]

CCing Andoni who added the passthrough support. I still can't get my 
head how alsasink will interact with the comprC%dD%d device node.

On 01/13/2015 10:04 AM, Qais Yousef wrote:
> On 01/13/2015 09:15 AM, Sebastian Dröge wrote:
>> On Di, 2015-01-13 at 08:40 +0000, Qais Yousef wrote:
>>> On 01/09/2015 09:28 AM, Qais Yousef wrote:
>>>> On 01/09/2015 09:12 AM, Sebastian Dröge wrote:
>>>>> Search for "MPEG" in
>>>>> http://cgit.freedesktop.org/gstreamer/gst-plugins-base/tree/ext/alsa/gstalsasink.c 
>>>>>
>>>>>
>>>>>
>>>>> At the sink pad template all the compressed formats that are 
>>>>> supported
>>>>> are in the PASSTHROUGH_CAPS #define.
>>>> OK that's awesome! I'll try it out.
>>>>
>>>>
>>> OK so I'm on gst v1.4.5, when I run this pipeline
>>>
>>>
>>>        gst-launch-1.0 -v filesrc location=$mp3_file ! mpegaudioparse !
>>> alsasink
>>>
>>> I get the following error:
>>> Setting pipeline to PAUSED ...
>>> Pipeline is PREROLLING ...
>>> /GstPipeline:pipeline0/GstMpegAudioParse:mpegaudioparse0.GstPad:src:
>>> caps = "audio/mpeg\,\ mpegversion\=\(int\)1\,\
>>> mpegaudioversion\=\(int\)1\,\ layer\=\(int\)3\,\ rate\=\(int\)44100\,\
>>> channels\=\(int\)2\,\ parsed\=\(boolean\)true"
>>> ERROR: from element
>>> /GstPipeline:pipeline0/GstMpegAudioParse:mpegaudioparse0: GStreamer
>>> encountered a general stream error.
>>> Additional debug info:
>>> gstbaseparse.c(3264): gst_base_parse_loop ():
>>> /GstPipeline:pipeline0/GstMpegAudioParse:mpegaudioparse0:
>>> streaming stopped, reason not-negotiated
>>> ERROR: pipeline doesn't want to preroll.
>>> Setting pipeline to NULL ...
>>> /GstPipeline:pipeline0/GstMpegAudioParse:mpegaudioparse0.GstPad:src:
>>> caps = "NULL"
>>> Freeing pipeline ...
>>>
>>>
>>> Looking at PASSTHROUGH_CAPS #define alsasink should support these caps,
>>> no? Do I need to insert something else into the pipeline?
>> No, AFAIK that should just work. If your driver and hardware supports
>> MP3 passthrough. You might also need to select a different device on
>> alsasink.
>>
>> If you get a debug log that might help.
>>
>>
>
> My driver is work in progress, but it works with cplay from 
> tinycompress[1].
>
> I changed my pipeline to specify the correct device
>
>    gst-launch-1.0 --gst-debug=3 -v filesrc location=$file ! 
> mpegaudioparse ! alsasink device="hw:0,1"
>
> now I get this:
>
> Setting pipeline to PAUSED ...
> 0:00:01.104003406   136 0x10070340 WARN                    alsa 
> pcm_hw.c:1557:snd_pcm_hw_open: alsalib error: open '/dev/snd/pcmC0D1p' 
> failed (-2): No such file or directory
> 0:00:01.110231370   136 0x10070340 WARN                    alsa 
> gstalsasink.c:846:gst_alsasink_open:<alsasink0> Error -2 (No such file 
> or directory) calling snd_pcm_open (&alsa->handle, alsa->device, 
> SND_PCM_STREAM_PLAYBACK, SND_PCM_NONBLOCK)
> 0:00:01.115911458   136 0x10070340 WARN                    alsa 
> gstalsasink.c:863:gst_alsasink_open:<alsasink0> error: Could not open 
> audio device for playback.
> 0:00:01.120933494   136 0x10070340 WARN                    alsa 
> gstalsasink.c:863:gst_alsasink_open:<alsasink0> error: Playback open 
> error on device 'hw:0,1': No such file or directory
> ERROR: Pipeline doesn't want to pause.
> ERROR: from element /GstPipeline:pipeline0/GstAlsaSink:alsasink0: 
> Could not open audio device for playback.
> Additional debug info:
> gstalsasink.c(863): gst_alsasink_open (): 
> /GstPipeline:pipeline0/GstAlsaSink:alsasink0:
> Playback open error on device 'hw:0,1': No such file or directory
> Setting pipeline to NULL ...
> Freeing pipeline ...
>
>
> which is wrong because it tries to open pcmC0D1 instead of comprC0D1
>
>    # ls /dev/snd/
>    comprC0D1  controlC0  pcmC0D0p   timer
>
> Maybe I specified the wrong name. In tinycompress they open the 
> compressed device using open()[2]. I'm not familiar with alsalib and 
> how it should handle this.
>
> [1] http://git.alsa-project.org/?p=tinycompress.git;a=summary
> [2] 
> http://git.alsa-project.org/?p=tinycompress.git;a=blob;f=compress.c;h=15dfdb74137ed0d1c7d65d8318391ac75ae79ee4;hb=HEAD#l240
>
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