Re: IOAudioDevice Startup Latency
Re: IOAudioDevice Startup Latency
- Subject: Re: IOAudioDevice Startup Latency
- From: Dirk Musfeldt <email@hidden>
- Date: Fri, 13 Dec 2002 21:03:10 +0100
>
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
>
>> _______________________________________________
>
>> coreaudio-api mailing list | email@hidden
>
>> Help/Unsubscribe/Archives:
>
>> http://www.lists.apple.com/mailman/listinfo/coreaudio-api
>
>> Do not post admin requests to the list. They will be ignored.
>
> _______________________________________________
>
> coreaudio-api mailing list | email@hidden
>
> Help/Unsubscribe/Archives:
>
> http://www.lists.apple.com/mailman/listinfo/coreaudio-api
>
> Do not post admin requests to the list. They will be ignored.
>
>
>
>
>
>
--
>
>
Jeff Moore
>
Core Audio
>
Apple
>
_______________________________________________
>
coreaudio-api mailing list | email@hidden
>
Help/Unsubscribe/Archives:
>
http://www.lists.apple.com/mailman/listinfo/coreaudio-api
>
Do not post admin requests to the list. They will be ignored.
_______________________________________________
coreaudio-api mailing list | email@hidden
Help/Unsubscribe/Archives:
http://www.lists.apple.com/mailman/listinfo/coreaudio-api
Do not post admin requests to the list. They will be ignored.