Fooling Around

DirectShow Filter Graph Spy was updated to add new functionality: spying over another DirectShow object – Filter Mapper. Filter Mapper object is used for filter registration purposes and also internally by DirectShow’s Intelligent Connect. IFilterMapper2 interface traces provide detailed description on steps DirectShow takes in order to connect  and/or render filter pins. For example when trying to render MEDIATYPE_Audio pin, Filter Mapper suggested “RDP DShow Redirection Filter” and, then, “Default DirectSound Device”:

FilterMapperSpy.h(186): CFilterMapperSpy::EnumMatchingFilters: nFlags 0x0, bExactMatch 0, nMinimalMerit 0x00200001, bInputNeeded 1, nInputTypeCount 1, pInputPinCategory NULL, bRender 1, bOutputNeeded 0, nOutputTypeCount 0, pOutputPinCategory NULL
FilterMapperSpy.h(191): CFilterMapperSpy::EnumMatchingFilters: nInputTypeIndex 0, MajorType {73647561-0000-0010-8000-00AA00389B71}, Subtype {00000000-0000-0000-0000-000000000000}
FilterMapperSpy.h(212): CFilterMapperSpy::EnumMatchingFilters: pMoniker @device:sw:{083863F1-70DE-11D0-BD40-00A0C911CE86}\{AB9D6472-752F-43F6-B29E-61207BDA8E06}
FilterMapperSpy.h(220): CFilterMapperSpy::EnumMatchingFilters: sFriendlyName "RDP DShow Redirection Filter", sDescription "", sDevicePath ""
FilterMapperSpy.h(212): CFilterMapperSpy::EnumMatchingFilters: pMoniker @device:cm:{E0F158E1-CB04-11D0-BD4E-00A0C911CE86}\Default DirectSound Device
FilterMapperSpy.h(220): CFilterMapperSpy::EnumMatchingFilters: sFriendlyName "Default DirectSound Device", sDescription "", sDevicePath ""

Important is that DirectShow’s internals are using the mapper through COM instantiation and this provides a safe method to override default behavior process wide in order to, for example, extend Intelligent Connect functionality onto custom, unregistered globally, private filters.

Also, the binary is renamed from FilterGraphSpy.dll to DirectShowSpy.dll.

Partial Visual C++ .NET 2008 source code is available from SVN, release binary included (Win32, x64); installation instructions are in another post.

Windows Media Codec List utility uses IWMCodecInfo interface (see also IWMCodecInfo2, IWMCodecInfo3) lists installed Windows Media Codecs and their formats and presents the findings in a convenient way. The utility gives a quick idea what a programmer would obtain through IWMCodecInfo2/IWMCodecInfo3 interfaces and what well known format structures (WM_MEDIA_TYPE, AM_MEDIA_TYPE, WAVEFORMATEX, VIDEOINFOHEADER) correspond to particular format.

For a description of Windows Media video and audio codecs, check article Encoding Audio and Video with Windows Media Codecs.

Copy button copies discovered information into clipboard in comma-separated values (CSV) format (e.g. suitable fo rMicrosoft Excel). Submit button posts the same information to this website for… possibly further aggregation.

Some quick facts immediately visualized by the utility:

• for a video codec there is exactly one generic codec format listed
• video codec FOUCCs are: WM Video – WMV1, WMV2, WMV3; WM Video Screen – MSS1, MSS2; WM Video Image – WMVP, WVP2; WM Video Advanced Profile – WVC1
• for audio codecs there are complete codec formats enumerated, with names/descriptions suitable for GUI
• audio codecs enumerate different formats in response to enumeration settings (e.g. request for VBR formats)
• WM Audio Lossless only lists formats for single pass VBR mode
• audio format tags (wFormatTag) are: WM Audio including Professional and Lossless – 0×0161, 0×0162, 0×0163; WM Audio Voice – 0×000A; ACELP.net – 0×0130

Partial Visual C++ .NET 2008 source code is available from SVN, release binary included.

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In order to obtain a reference audio source and especially useful for debugging purposes, including:

• audio input device unrelated to physical device, to avoid conditions when device is already in use by someone else
• non-zero audio signal which is independent of certain speaker or broadcasting service, including one that makes capture, transmission or rendering issues easily perceptible by human
• configurable to provide different audio media types, including through well known DirectShow interfaces, such as IAMStreamConfig
• configurable to present in system as both regular DirectShow Filter, and as an Audio Capture Source which can be enumerated by applications
• to be able to check how exactly other applications are accessing and configuring audio capture source

I added a new filter to the Media Tools library, a Tone Source Filter. The filter generates PCM Audio data, either infinite sine waveform, or interrupted signal  of requested parameters:

The filter accepts connection on PCM media types with flexible sampling rates in range 8 KHz through 200 KHz, 8-bit audio and 1 channel. Media type is also configurable through or, if not configured this way, the first enumerated media type off the Output pin is also configurable through property page and/or persistent setting accessible via private IDispatch derived interface property.

Additionally, the filter may configured as a system-wide available audio input device, such as for example available to VLC Media Player or Media Player Classic:

In order to configure the filter as such device, the library exports function DoToneSourceFilterDevicePropertySheetModal, which can be called using rundll32 utility (“rundll32 Acquisition.dll,DoToneSourceFilterDevicePropertySheetModal” from command line):

A partial Visual C++ .NET 2008 source code is available from SVN, release binary included.

File and Class Summary

Acqusition.dll

Acqusition.dll (download) hosts the following classes:

• DirectShow Filters
  • Tone Source Filter, to generate reference/debug audio data

Class Overview

Tone Source Filter

The filter generates uninterrupted or interrupted reference sine waveform in form of PCM audio data.

• Filter Executable: Acquisition.dll
• Filter CLSID: __uuidof(ToneSourceFilter) {8002935A-B2EC-40ef-968C-E0358E5DED10}
• Filter Property Page CLSID: __uuidof(ToneSourceFilterGeneralPropertyPage), {EBD8ABB2-6DD3-4c54-A7F1-9FE4DA283EDF}, ToneSourceFilterPreferedFormatPropertyPage, {EE224187-4FA3-4c3f-9D5D-492694CCFEB7}
• Filter Merit: MERIT_DO_NOT_USE
• Filter Category: CLSID_LegacyAmFilterCategory (also configurable as CLSID_AudioInputDeviceCategory)
• Filter Interfaces: IPersistStreamInit, IPersistStream, ISpecifyPropertyPages, IPersistPropertyBag, IBaseFilter, IMediaFilter, IPersist, IAMovieSetup, IAMFilterMiscFlags, IToneSourceFilter, IDispatch
• Filter Pins: single ouput pin (Ouput)
• Output Pin Media Types: MEDIATYPE_Audio/MEDIASUBTYPE_PCM
• Output Pin Interfaces: IPin, IMemInputPin, IAMPushSource, IAMLatency, IAMBufferNegotiation, IKsPropertySet, IAMStreamConfig

Remarks

The hosting library (DLL) exposes DoToneSourceFilterDevicePropertySheetModal function which provides GUI to configure the filter as one or more audio capture source device, which can be enumerated by System Device Enumerator.

I don’t have any idea who makes software nowadays, but how can it expected to be reliable?

Intel DG33FBC motherboard, onboard Realtek ALC888 High Definition Audio. I am tracing AUDIO_STREAM_CONFIG_CAPS capabilities reported by onboard audio capture board, one of them:

AM_MEDIA_TYPE:

majortype {73647561-0000-0010-8000-00AA00389B71}, subtype {00000001-0000-0010-8000-00AA00389B71}, pUnk 0x00000000
bFixedSizeSamples 1, bTemporalCompression 0, lSampleSize 4
formattype {05589F81-C356-11CE-BF01-00AA0055595A}, cbFormat 18, pbFormat 0x002911a8
pbFormat as WAVEFORMATEX:
  wFormatTag 1
  nChannels 2
  nSamplesPerSec 8000
  nAvgBytesPerSec 32000
  nBlockAlign 4
  wBitsPerSample 16
  cbSize 0

AUDIO_STREAM_CONFIG_CAPS:

guid {73647561-0000-0010-8000-00AA00389B71}
MinimumChannels 1, MaximumChannels 2, ChannelsGranularity 1
MinimumBitsPerSample 8, MaximumBitsPerSample 16, BitsPerSampleGranularity 8
MinimumSampleFrequency 11025, MaximumSampleFrequency 44100, SampleFrequencyGranularity 11025

Media type sampling frequency is 8 KHz (correct) but associated capabilities structure still report different sampling rates and granularity (crap), it is in fact 11025..44100 Hz for all capabilities, including those with sampling frequencies from a different row.

There has been recently an interesting post “Problem playing back multi-channel wave file under vista” on DirectShow Development forum about certain hardware that is capable of recording 64 channels of audio in 24-bit per sample PCM quality, with a sample recorded .WAV file posted.

I was curious what kind of hardware implements such recording. Google suggests it could be PCM H64 multichannel system from Sadie, UK.

This is definitely an interesting piece of hardware which can fill normally video’s bandwidth with audio only data. BTW, some useful related C++/DirectShow code is here on new Assembla’s web itnerface into subversion repository.

IDirectSoundNotify8 is an interface to get notified on playback on capture audio buffer reaching certain position in the buffer. It is a must thing when implementing ring buffers with new data continuously added to the buffer for seamless playback (continuously copied from in case of capture).

This project is a minimalistic C++ sample code to illustrate the API. To initialize the DirectSound subsystem it is required to provide a window handle, which is created using ATL’s CWindowImpl (CMessageOnlyWindowImpl).

...
ATLENSURE_SUCCEEDED(DirectSoundCreate8(NULL, &pDirectSound8, NULL));
...
ATLENSURE_SUCCEEDED(pDirectSound8->SetCooperativeLevel(Window, DSSCL_PRIORITY));
...
ATLENSURE_SUCCEEDED(pDirectSound8->CreateSoundBuffer(&BufferDescriptor, &pDirectSoundBuffer, NULL));
...
CComQIPtr<IDirectSoundNotify8, &IID_IDirectSoundNotify8> pDirectSoundNotify8 = pDirectSoundBuffer;
...
ATLENSURE_SUCCEEDED(pDirectSoundNotify8->SetNotificationPositions(g_nPositionCount, pPositionNotify));
ATLENSURE_SUCCEEDED(pDirectSoundBuffer->Play(0, 0, DSBPLAY_LOOPING));

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Surprisingly fast I got new problems having ffdshow installed as a part of K-Lite Codec Pack. No wonder though because let us take a look at registration information:

Display Name: @device:sw:{083863F1-70DE-11D0-BD40-00A0C911CE86}\{0F40E1E5-4F79-4988-B1A9-CC98794E6B55}
CLSID: {0F40E1E5-4F79-4988-B1A9-CC98794E6B55}
Friendly Name: ffdshow Audio Decoder
Path: C:\Program Files\K-Lite Codec Pack\ffdshow\ffdshow.ax
Merit: 0×3fffffff

Nice merit, ain’t it? What is merit anyway? Let us check at MSDN:

MERIT_PREFERRED = 0×800000,
MERIT_NORMAL = 0×600000,
…
MERIT_HW_COMPRESSOR = 0×100050

The highest defined value is 0×00800000, while ffdshow is registered with 0×3FFFFFFF, that is on top of everything. No doubt the developers read Guidelines for Registering Filters and decided to get rid of the rest of installed software as unnecessary crap.

Anyway back to the problem: I had an A-law wave file (WAVE_FORMAT_ALAW) to play and make sure its data is valid and quite unexpectedly there was a silence while playing. A quick check confirmed that the sustem has CCITT A-law codec installed, however GraphEdit shown ffdshow Audio Decoder intercepting decoding. Obviously it spoiled the thing!

Finally I decided it was a right time to take an advantage of IAMGraphBuilderCallback interface to detect and reject the bastard.

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