[mythtv-users] frustrating comments about sample rates (what not to do)

[Larry Symms]

I know the difference, the problem is, the user who doesn't go digging 
through code would have no indication that changing the sample rate for 
recording profiles of an mpeg device would have negative effects, which 
aren't immediately obvious.  Why would I change the rate you ask?  The 
default alsamixer settings for my audio card (which uses the Via Envy24 
chipset) sets "multi track rate locking" to on, so I set the alsamixer 
multi track sample rate to 44.1kHz so that it would work with TV and 
music.  I changed the recording profile rates to 44.1kHz and didn't 
realize there was a problem for a few weeks because this only happens 
when watching recordings as they're recording or buffered live TV which 
I do very rarely.

Donavan Stanley wrote:

>On 8/29/05, Larry Symms <lsymms at comcast.net> wrote:
>  
>
>>In mpegrecorder.cpp it states "// only 48kHz works properly." regarding
>>audio sample rates which I have tested and proven true.  What happens is
>>a discrepancy in displayed time and actual position in the recording.
>>This leads to skipping back when trying to skip forward because myth is
>>miscalculating the current position based on time elapsed.  The problem
>>is that the comments in Recording Profiles in TV Settings in Myth
>>frontend say: "Sets the audio sampling rate for your DSP.  Ensure that
>>you choose a sampling rate appropriate for your device.  btaudio may
>>only allow 32000."  This implys that not only is it ok to change the
>>sampling rate from the default but that it is recomended.  This is not
>>the case.  Do not be deceived, 48000 is the only acceptable setting for
>>mpeg encoders unless you never watch recordings while they're
>>recording.  When playing recordings while they are recording the sample
>>rate is gathered from the codec settings in the db rather than the mpeg
>>header.  If any of this is incorrect by all means correct me but I'm 99%
>>sure this is the case based on the code I've gone through and the tests
>>I've conducted.
>>    
>>
>
>
>The big thing you appear to be missing is the btaudio and mpegrecorder
>have nothing to do with each other.  If you have a card which uses
>btaudio you're going to be using nupplevideoencoder.
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>  
>