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Re: IOAudioDevice Startup Latency
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Re: IOAudioDevice Startup Latency

> I think you are saying that you are observing an offset between the
> video and the audio when digitizing with Quicktime.

Correct.

I don't provide a clock component as my device has no internal timing. I
could just provide the system time. But I didn't see any advantage in that.

I experimented a lot with latency and sample offset but that only made it
worse.

How should I measure that exactly?



With kind regards

Dirk Musfeldt
Meilenstein Mac OS Software

Neue Strasse 5
D-31582 Nienburg
Germany
Tel: +49 (0) 5021 91 24 44
Fax: +49 (0) 5021 91 24 45
<http://www.meilenstein.de/>


> Von: Jeff Moore <email@hidden>
> Datum: Thu, 12 Dec 2002 12:17:07 -0800
> An: CoreAudio API <email@hidden>
> Betreff: Re: IOAudioDevice Startup Latency
>
>
> Does your vdig provide a clock component? If not, it should.
>
> Does your IOAudio driver have the correct values for the latency and
> safety offset properties? It's easy to get these wrong. The latency is
> the number of samples frames at the current sample rate it takes from
> when the DMA gets the data to when it shows up on the line. The safety
> offset describes not just the physical requirements of the DMA
> hardware, but also needs to reflect the jitter in the time stamps. You
> need to spend some time measuring this and increase your safety offset
> accordingly.
>
> There are some other wrinkles in doing some of this stuff, particularly
> on the QT side. There's probably a lot of stuff that we just can't
> cover in email, so I would encourage you to get in touch with Developer
> Relations.
>
> On Thursday, December 12, 2002, at 06:23 AM, Dirk Musfeldt wrote:
>
>> No, I don't think that is true.
>>
>> I don't know how to measure exactly what is happening, but I have
>> audio DMA
>> as well as video DMA.
>>
>> The audio DMA goes into my IOAudioEngine and is output by CoreAudio
>> and the
>> video DMA goes into a QuickTime vdig.
>>
>> I have observed a latency between the audio output from CoreAudio and
>> the
>> video output as well as between the audio output from CoreAudio and the
>> DAC's line out signal.
>>
>> The video output and the DAC's signal are in sync so that I can't
>> imagine
>> the latency being in the DMA stream.
>>
>>
>> With kind regards
>>
>> Dirk Musfeldt
>> Meilenstein Mac OS Software
>>
>> Neue Strasse 5
>> D-31582 Nienburg
>> Germany
>> Tel: +49 (0) 5021 91 24 44
>> Fax: +49 (0) 5021 91 24 45
>> <http://www.meilenstein.de/>
>>
>>
>>> Von: Jeff Moore <email@hidden>
>>> Datum: Wed, 11 Dec 2002 11:24:00 -0800
>>> An: CoreAudio API <email@hidden>
>>> Betreff: Re: IOAudioDevice Startup Latency
>>>
>>> So if I'm understanding what you are saying correctly, you have
>>> observed a latency between when the data is bussed to your card (by
>>> DMA
>>> or some other way?) and when your card's DAC's put the signal on the
>>> line. If that's right, that sounds like a hardware issue with how your
>>> card interfaces with the PCI bus. This is probably not the best forum
>>> for your question in that case, but perhaps I'm misunderstanding?
>>>
>>> On Wednesday, December 11, 2002, at 07:11 AM, Dirk Musfeldt wrote:
>>>
>>>> Hi all,
>>>>
>>>> I have a PCI device that has audio and video output over PCI as well
>>>> as a
>>>> line out port.
>>>>
>>>> I observe an offset between the audio over PCI and the audio over the
>>>> line
>>>> out port. I have difficulties to measure the exact amount of the
>>>> offset but
>>>> I think it is about 500 msec.
>>>>
>>>> Of course there has to be an offset but I think it should be less
>>>> than
>>>> 500
>>>> msec.
>>>>
>>>> How could I minimize the offset?
>>>>
>>>>
>>>>
>>>> With kind regards
>>>>
>>>> Dirk Musfeldt
>>>> Meilenstein Mac OS Software
>>>>
>>>> Neue Strasse 5
>>>> D-31582 Nienburg
>>>> Germany
>>>> Tel: +49 (0) 5021 91 24 44
>>>> Fax: +49 (0) 5021 91 24 45
>>>> <http://www.meilenstein.de/>
>>>
>>> --
>>>
>>> Jeff Moore
>>> Core Audio
>>> Apple
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>>
>
> --
>
> Jeff Moore
> Core Audio
> Apple
> _______________________________________________
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References: 
 >Re: IOAudioDevice Startup Latency (From: Jeff Moore <email@hidden>)



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