flac dev - Sep 2004 - Re: FLAC format

Hi,
>That's what I wanted to say a month ago.
Mr. Blum, I'm really sorry for misunderstanding you. My mistake. I choose an
ACM codec because it's the only option that works on every Windows Platform,
and since the DirectShow has a generic wrapper that allows it to use ACM
codecs, it appeared a good idea. I didn't note that the file format was
going to be a problem. But I think a have a solution that can allow me to
achieve my initial goal of compatibility. I can simple write a DirectShow
source filter to read the FLAC file, then the ACM codec can treat the
stream. And the AVIs with embedded FLAC audio will be readable in every
Windows Platform.
>Have you tried to use a WAVEFORMATEXTENSIBLE? This should make registration
obsolete.

I believe the WAVEFORMATEXTENSIBLE structure is available only for WDM audio
drivers. Is it true? The WDM drivers are included with all the necessary
functionality only in Windows 98SE or later. I think it's a big problem.
What do you think?

Regards,
Daniel

Hi Daniel,
> Mr. Blum, I'm really sorry for misunderstanding you. My mistake. I
choose an
> ACM codec because it's the only option that works on every Windows
Platform,
> and since the DirectShow has a generic wrapper that allows it to use ACM
> codecs, it appeared a good idea. I didn't note that the file format was
> going to be a problem. But I think a have a solution that can allow me to
> achieve my initial goal of compatibility. I can simple write a DirectShow
> source filter to read the FLAC file, then the ACM codec can treat the
> stream. And the AVIs with embedded FLAC audio will be readable in every
> Windows Platform.
I started a single DirectShow filter for FLAC playback, which does the decoding
inside it, but I think your solution with the combination of a reader filter and
the ACM wrapper is a better aproach and I should drop mine. (Fortunately
I've
just started).
> >Have you tried to use a WAVEFORMATEXTENSIBLE? This should make
registration
> obsolete.
>
> I believe the WAVEFORMATEXTENSIBLE structure is available only for WDM
audio
> drivers. Is it true? The WDM drivers are included with all the necessary
> functionality only in Windows 98SE or later. I think it's a big
problem.
> What do you think?
It is just a WAVEFORMATEX with a GUID in it. For the ACM system it is just a
format with the id WAVE_FORMAT_EXTENSIBLE and since ACM drivers are not
registered by wFormatTag it should be working. For testing purposes I've
written
a Vorbis ACM driver, that uses a WAVEFORMATEXTENSIBLE and I experienced a
problem when opening files with Media Player. It spend quite some time at 100 %
CPU doing nothing (from the users perspective). However the problem might have
come frome either the fact, that the driver was compression only or that it
collided with a DirectShow filter, that I've written for decompression. I
haven't gone after it yet.

Regards,

Ingo

Hi Daniel,

I have another question.

For format negotiation the driver must return a bunch of fully specified
formats. Then a suitable format is choosen from the returned set by the
application and then set back as the output format for compression. At least
this is what VirtualDub does. This means, that all available format variations
must be returned. I find this stupid, because the more compression options you
have, the more different formats exist. This is at least the case, when all
required information for decompression is put into the WAVEFORMATEX, which is
the case for my Vorbis filters.

Do you see a problem here or does Virtual Dub not what it should?

Regards,

Ingo