Bug in DirectShow Codec

[JoeRip]

I'm isolating this from another thread. The intention here is to report a bug in the DirectShow Codec.

Summary: dMC fails to convert AC3 file when AC3 Filter output has channels > 2 or sample rate > PCM 16 bit.

Expanded Summary:

With dMC DirectShow Codec installed and configured, and the AC3 DirectShow Filter installed and configured, dMC fails to convert an AC3 file if the AC3 Filter is configured with any settings except default.

Specifically, if the AC3 Filter is set to Channels ("Speakers") > 2, or "PCM Sample Rate" > 16, then a TEST Conversion yields the following error: "The CODEC required to decompress 'C:\foo.AC3' could not be opened. Unable to insert SampleGrabber."

To reproduce:

1. Download and install the dMC DirectShow Codec from (http://www.dbpoweramp.com/codec-central-directshow.htm)

2. Download and install the AC3 DirectShow Filter from SourceForge (http://prdownloads.sourceforge.net/a....exe?download). Do not change the AC3 Filter's defaults.

3. Using DVD Decryptor or IMToo's DVD Ripper, Export a 5.1 AC3 stream ("foo.ac3")

4. Without changing the AC3 Filter defaults, do a TEST Conversion using dMC on "foo.ac3". Conversion completes without error.

5. Using the AC3 Filter Configuration Dialog (Start Menu -> All Programs -> AC3 Filter -> AC3 Filter Config), in the Output group box change the number of channels ("Speakers") to anything but 1/0 (mono) or 2/0 (stereo). OR, change the "Sample Rate" to anything other than PCM 16. Save and closed dialog.

6. Using dMC, run a Test Conversion on "foo.ac3".

Result: Error Dialog, "The CODEC required to decompress 'C:\foo.AC3' could not be opened. Unable to insert SampleGrabber."

Either the AC3 Filter is not outputting correct format once you change it's options (doubtful - it's an established tool, used by other applications), or dMC is not correctly handling the output (more likely).

This is not likely to be relevant, but the AC3 file I'm converting has the following properties:

Sampling Frequency: 48 kHz
Bit Rate: 448 kbps
Audio Coding Mode: 3/2
Channels: 5 (6 including LFE)
Low Frequency Effects: Yes
Center Mix Level: 0.707 (-3.0 dB)
Surround Mix Level: 0.707 (-3.0 dB)

[LtData]

Re: Bug in DirectShow Codec

Can you play your the multi-channel .ac3 file in Windows Media Player?

[JoeRip]

Re: Bug in DirectShow Codec

No I can't, as WMP does not recognize AC3 files natively. Simply installing the AC3 DS Filter does not enable WMP to recognize an AC3 file, either.

But the file is not the problem here. Note that the TEST conversion works if you do not alter the output of the AC3 filter. It's only if you change the options in the AC3 filter that the TEST conversion fails.

[JoeRip]

Re: Bug in DirectShow Codec

I stand corrected. I was able to force WMP to open the AC3 file - all of them. WMP just didn't know it was allowed to.

Yes, they all play in WMP 10. I'm not able to tell if they are using all 6 channels, though. WMP isn't able to specify any attributes for the file being played, and although I get distribution across all 5 speakers, that could be downsampling on WMP's part.

So, the files are good. The problem lays in either (a) the output from the AC3 filter - which, again, I doubt - or in how dMC handles the output.

[JoeRip]

Re: Bug in DirectShow Codec

And, in fact, WMP is handing the AC3 Filter output when it has been changed. If I change the filter from 2 Channel / 16 bit to 5.1 Channel / 24 bit, I can hear the difference in WMP.

(This can't be done on the fly, you have to close WMP between Filter Configs).

So, again, this suggests that dMC is having problems with the AC3 Filter output, yet WMP is able to read it correctly.

[Spoon]

Re: Bug in DirectShow Codec

Noted as a bug, thanks for the report.

[JoeRip]

Re: Bug in DirectShow Codec

You are welcome.