[alsa-devel] [tinycompress]how should I call compress_open for aac ltp file playback?

Vinod Koul vinod.koul at intel.com
Fri Jun 7 02:23:08 CEST 2013

On Wed, Jun 05, 2013 at 04:27:44PM +0800, Keyon.Jey wrote:
> On 06/05/2013 04:01 PM, Charles Keepax wrote:
> >On Wed, Jun 05, 2013 at 02:46:04PM +0800, Keyon.Jey wrote:
> >>I am trying to use tinycompress for hwdecoder. everything works fine,
> >>but after compress_open (with profile = SND_AUDIOPROFILE_AAC level=0
> >>ch_mode=0 rate_control=0), the playback of my aac-ltp-16bit-48KHz-Stereo
> >>file is faster than it should be.  Am I wrong?
> >Vinod is probably the person for this one, as I am not so
> >familiar with what you guys have done internally. However, my
> >guess would be you are not setting the sample_rate correctly? It
> >likely needs to be set to the appropriate SNDRV_PCM_RATE_XXXX
> >define. The source for cplay included in the tinycompress
> >repository is a good example of using the tinycompress library.
> >
> thanks, Charles. the print log showed me that I have set
> SNDRV_PCM_RATE_48000 which seems no problem.
> the cplay example code is only for mp3 file, and it also not set
> .level, .ch_mode and .rate_control.
> Vinod, what's your suggestion?
You need to ask your firmware guys, what are they expecting the these fields.
Some decoder implementations can be different. But i would expect the audio to
be broken, bad quality if that is the case.

But the speed of playback can be due to different decoder output rate and
different sampling rate configured. You are telling decoder 48Khz as CPM sample
rate, is that what decoder is understanding and conversion to decoder values
correct. Then you should check if the rendering to DAC is at 48KHz or not.


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