[Flac-dev] Re: FLAC format

Ingo Ralf Blum ingoralfblum at gmx.de
Mon Oct 1 18:32:02 PDT 2001

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.



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