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List:       helix-audio-dev
Subject:    Re: [Audio-dev] CR : Fix for audio jitters on audio start-up on
From:       Eric Hyche <ehyche () real ! com>
Date:       2010-01-14 14:38:42
Message-ID: 8BE738BC-E1FF-42D4-9DBE-303FD89E693E () real ! com
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How does this change prevent us overwriting the ALSA buffer? It looks like all we are \
doing is making a different call to write from our internal audio buffer to the ALSA \
API. So if there is a bug in overwriting the ALSA buffer, it would seem like it still \
exists after this change.

Also, is there not an API in ALSA to tell whether or not the buffer you are about to \
overwrite is still "active" (has not been played yet)?

I still don't understand what the bug is, and why this change fixes it.

Eric

On Jan 13, 2010, at 6:59 AM, Deepak Jain wrote:

> In MMAP access mode, we write directly to a memory pointer.
> In the LG-ARM device, when using non-MMAP mode, it looks like jitters 
> are caused by the player overwriting the ALSA buffer.
> When the buffer is full the application should not write into the 
> buffer, otherwise it will overwrite old samples. This looks like what 
> the application is doing.
> 
> Thanks,
> Deepak Jain
> 
> 
> Eric Hyche wrote:
> > Change looks fine, but I'd like to understand more the differences between the \
> > two modes and why MMAP access mode fixes this particular problem. Can you tell me \
> > the difference between these two access modes and why MMAP access mode is \
> > preferable for LG-ARM? Why does changing the access mode fix this problem of \
> > audio "jitters" at startup? 
> > Eric
> > 
> > On Jan 12, 2010, at 6:56 AM, Deepak Jain wrote:
> > 
> > 
> > > Project: Real Player for MID - ARM.
> > > 
> > > Synopsis: Fix for audio jitters on audio start-up on LG-MID ARM device
> > > 
> > > Overview: When we play any file on LG-MID ARM device, we hear small audio \
> > > jitters during playback startup. These jitters remain for 2-3 seconds and after \
> > > that the audio jitters go away. 
> > > Currently we are using RW access mode. If we use MMAP access mode, and then \
> > > instead of snd_pcm_writei() API, use snd_pcm_mmap_writei() API in \
> > > _WriteBytes(), we do not hear any jitters on start-up. 
> > > A new config define HELIX_CONFIG_PCM_MMAP is applied for enabling/disabling \
> > > mmap mode. 
> > > Files Modified:
> > > audio/device/platform/unix/audlinux_alsa.cpp
> > > 
> > > Image Size and Heap Use impact (Client -Only):
> > > None.
> > > 
> > > Platforms and Profiles Affected:
> > > None.
> > > 
> > > Distribution Libraries Affected:
> > > None.
> > > 
> > > Distribution library impact and planned action:
> > > None.
> > > 
> > > Platforms and Profiles Build Verified:
> > > BIF: hxclient_3_4_11_atlas_restricted
> > > Target: player_mid_all_installers
> > > Profile: helix-client-mid-arm
> > > 
> > > Branch:
> > > Atlas_3411
> > > 
> > > Files Attached:
> > > audlinux_alsa.diff
> > > 
> > > Thanks,
> > > Deepak Jain
> > > 
> > > <audlinux_alsa.diff><ATT00001..txt>
> > > 
> > 
> > Eric Hyche (ehyche@real.com)
> > Principal Engineer
> > RealNetworks, Inc.
> > 
> > 
> > 
> > 
> 

Eric Hyche (ehyche@real.com)
Principal Engineer
RealNetworks, Inc.



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