Why are the Multimedia Timer APIs (timeSetEvent) not as accurate as I would expect?

The Multimedia Timer APIs (MM Timer APIs) get their high accuracy by using the Programmable Interrupt Controller (PIC) built into the hardware on the machine. By default Windows specifies a PIC duration of about 10 – 16 milliseconds. Every time the PIC fires the operating system kernel “wakes up”. Any executing user-mode threads are suspended…

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Here is a consolidated list of changes that we can expect for DirectShow Windows 7

Potentially Breaking Change (*IMPORTANT*): Intelligent Connect adds a level of indirection on Win 7 that may have a major impact to DirectShow developers. Starting in Windows 7, DirectShow has a list of preferred filters for certain media subtypes. If there is a preferred filter for the media type that is being rendered, the Filter Graph…

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Activating an audio endpoint when not connected causes the device to report incorrect capabilities

The other day we had a major OEM report an issue with the WASAPI. In particular when they found that when they called “IAudioEndpointVolume::QueryHardwareSupport” it would occasionally return unexpected results for USB web cam devices. Most of the time calling this method would return a full list of capabilities for the device. Occasionally this method…

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Exception playing .mp3 & .wma files using embedded WMP from .hta files

We recently had an engineer report a strange exception when displaying .hta files via mshta.exe. If you embed the Windows Media Player OCX control (WMP) in a web page and then start playback of a file, you will get an exception like the following: Windows – Bad ImageException Processing Message 0xc000007b Parameter 0x760892A0 0x760892A0 0x760892A0…

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Playing an MPEG1 file in WMP via HTTP returns the wrong duration

A colleague of mine in Japan recently found this very interesting issue in Windows Media Player (WMP) on Windows XP. From what he found WMP returns the wrong duration value when playing back MPEG1 files via HTTP. This only appears to occur if the file has not been cached locally by the player. This issue…

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DirectShow Filter vs. DMO – Ready… Fight!

There are some rather interesting misunderstandings surrounding Direct Media Objects (DMO). I talked to one engineer the other day that called DMOs inferior to DirectShow filters. While I personally think that DirectShow is one of the most amazing technologies of all time, times are changing. From what I understand, the DMO actually got its start…

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Rendering MMS, RTSP and HTTP with DirectShow in Vista and Windows 7

I was talking to a DirectShow engineer the other day that was having issues rendering URLs using DirectShow on XP and Vista. He noticed that the behavior was very different between the two operating systems. Luckily I was privy to a very interesting conversation between the original developer of the WM ASF Writer filter and…

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