Fooling Around

// Oprogramowanie Roman Ryltsov

Category: LinkedIn

Cross-posted from LinkedIn company profile

LDS Temples and Technology: The DirectShow Journey

Posted on by Roman

A while back, we were working on a media subsystem for The Church of Jesus Christ of Latter-day Saints. They needed software-controlled multimedia playback with specific requirements for their temples worldwide.

Now, the attached image isn’t an exact representation of our work, but it captures the essence: LDS and technology go hand in hand.

Back in the day, we used #DirectShow as our multimedia framework, and boy, did we face some interesting challenges. One that sticks out in memory is related to audio delivery. Picture this: we had a multi-channel audio output card from AudioScience, Inc., and our task was to schedule audio delivery in perfect sync across multiple physical audio connectors. But wait, there’s more! We also had to toggle outputs on and off while others were already belting out sound. And when we turned on a fresh audio stream, it had to seamlessly match the signal already in play. Oh, and don’t forget — the video part of this signal was streaming nonstop and couldn’t be interrupted.

Now, let me tell you, this wasn’t a walk in the park. The multimedia framework was designed back in the ’90s, with the quaint notion that once you set up your playback topology, you couldn’t tweak anything while the show was running.

But guess what? Our software spread its wings and flew to over a hundred locations worldwide. Many moons have passed, but who knows — it might still be chugging along out there.

Legacy Filters, Modern Solutions: MP4 Support in DirectShow

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Microsoft #DirectShow API was introduced long before the widespread adoption of MPEG-4. As MPEG-4 codecs and container formats became standard, DirectShow was, by Microsoft’s own admission, nearing the end of its life.

That’s how this once-popular media framework for Windows found itself without support for MP4 files. Fortunately, there was a handy solution: freely available filters https://gdcl.co.uk/mpeg4/ developed by Geraint Davies. Originally published in 2006, these filters gained popularity over time. Since Geraint had other commitments after the last update, we took the liberty of placing a copy of his work on GitHub https://lnkd.in/dPsZEfpE somewhere around 2015.

Despite the state of DirectShow, these filters still play a role in DirectShow applications. We’ve even made a few updates ourselves — a little bit of everything: a unit test project, some modern C++ and #COM code based on Microsoft WIL https://lnkd.in/de5nxif, a COM type library with an integration interface, and various features. One particularly valuable addition is the ability to recover broken recordings.

You see, sometimes applications crash — whether due to external factors or just plain bad luck. And sometimes the cost of “re-doing things right” is too high. Oh, and the cost of data loss is high too! In such cases, we can salvage the broken recording from the crashed application and recover its content. It’s like a digital rescue mission. And in some instances, it’s even automated — like in our partner’s medical software https://lnkd.in/dCrJJRjy, where multi-hour recordings are the norm these days.

Breaking the Rules: A Quick and Dirty Approach to FX Trading Automation

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One of the truly unconventional development projects was our development of specialized automated agent for foreign exchange (FX) trading.

The customer wanted to implement their unusual ideas at one (and then another) of the popular electronic Forex market trading platforms. The key idea was to be a market maker and a liquidity provider agent, and also to be able to provide the fastest reaction to market events.

Applications like this, that are touching big/real money are normally developed in respective way: robust tooling, a well-established software stack, comprehensive unit test coverage, peer-reviewed code, and thorough documentation.

We were breaking all the rules! That time we took a different approach — a quick and dirty one.

Singlehandedly and rather straightforwardly, we implemented a #FIX (Financial Information eXchange) client in C++ addressing ultra-low latency, and the application was running on a box connected via secure fiber connection with the platform data center located in neighboring building.

At the peak of the swing, we had positions at CurrenEx worth a jaw-dropping $15 million. Yeah, you read that right. Fifteen million bucks!

Custom Filters to the Rescue: Diagnosing and Solving Media Stream Woes

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In a recent customer project, we encountered a longstanding problem related to a broadcasted media stream captured by software.

Our customer application, built on the hashtag#DirectShow framework, was responsible for capturing the media stream. The application needed to operate 24/7 and maintain stability during continuous live media broadcasting.

Unfortunately, sporadic crashes occurred due to a third-party DirectShow filter within the topology. This filter triggered memory access violations and crashed the entire application. The vendor of this problematic component was unavailable for maintenance. Given the low incident frequency, the customer was concerned about possible regressions in the case of any update of this part of the application.

The issue manifested only in the production signal, complicating troubleshooting, and the customer’s data center required remote access via VPN and several remote desktops.

To diagnose and solve the problem effectively, we introduced a lightweight DirectShow filter. This custom filter transparently captured a dump of the recently captured MPEG-TS signal, mirroring the data flow to the faulty component. In the production environment, this solution allowed us to analyze the content in sufficient detail to reproduce the problem outside the production setup.

Eventually, we replaced the problematic third-party DirectShow filter with an in-house development that handled that particular processing step reliably and maintainably.

In summary, our custom DirectShow filter provided crucial insights, enabling us to address the issue and enhance stability in the customer’s live media broadcasting application.

From Webcams to 24-Hour Recordings: A Decade of Medical Video Evolution

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For over a decade, we have been supporting a customer’s product in the field of medical video. Our journey began with their attempts of previous years to record from webcams — an endeavor that was initially partially successful. We put our expertise to bring use of this technology to stable level, and since then we have successfully captured countless hours of footage, using both standard cameras and professional-grade hardware.

One particularly intriguing aspect of this evolution stands out.

In the early days, our recordings were typically brief, lasting only a few minutes. Moreover, the original implementation imposed a strict 10-minute limit within the application. Why? Well, at that time, there was no robust video encoder available that could handle the application’s requirements — hardware constraints, desired quality, and real-time performance. Consequently, the signal was often recorded in an uncompressed format. The time limit served a purpose: managing disk usage and preventing accidental overflows.

As the years passed, we transitioned to using proper video encoders for live content. We swiftly expanded our supported resolution to Full HD at 60 frames per second. Hardware-assisted encoding became the norm, and the duration of encoded sessions gradually increased. What started as 10-minute recordings soon extended to 15 minutes, half an hour, and eventually full procedures lasting up to 4 hours. Then came the pivotal question: “Can we record continuously for 24 hours?” The answer was a resounding yes.

Despite its long history, the ongoing support, stable performance, and improvements over time have been well worth the very moderate effort, and yes, it’s still a hashtag#DirectShow app. With a little hashtag#MediaFoundation insertion.

Simultaneously, the need for data safety during recording intensified. Fortunately, we devised a solution, which we’ll delve into further in an upcoming piece.

Windows 11 Virtual Camera: Real-Time Video with Minimal Latency

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A customer approached us to create a virtual camera subsystem for Windows tailored to their specific use case. Their application required a video feed from either a built-in or externally connected camera. Simultaneously, they wanted to make this camera accessible to other applications.

As previously mentioned https://lnkd.in/dYte5SQ5, this longstanding challenge had been addressed through specific development, with the open-source sample known as “VCam” serving as the starting point. Remarkably, VCam predates even Stack Overflow itself. Yet recently there have still been inquiries related to VCam, as evidenced by discussions on Stack Overflow: https://lnkd.in/dyu_Ypta.

However, with the advent of Windows 11, Microsoft finally provided a solution to the virtual camera conundrum as part of their #MediaFoundation API, codenamed “MFCreateVirtualCamera”. We successfully implemented this solution for our customer. In addition to the proof of concept https://lnkd.in/djy7Uq3w that we shared in 2022, this marked our first production use of this new technology.

In essence, we re-established a #realtime video feed with nearly zero latency, effectively treating it as an independent source of video signal.

VCam: A Journey from Usenet to GitHub

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Throughout many years of hashtag#DirectShow development, one project stood out with unwavering popularity: the Windows Virtual Camera sample ????. Originally authored by Vivek in 2005 or even earlier, it was shared on the “microsoft. public. win32. programmer. directx. video” Usenet conference. This project gained prominence because it addressed a problem that had no existing solution within the Windows SDK, and Microsoft had not expressed any intention to rectify it.

The source code for this virtual camera project was once hosted by Philip “The March Hare” on his personal website. However, given the passage of time, even that website does not longer exist.

We decided to breathe new life into this project, affectionately known as “VCam”, and made it available on GitHub: https://lnkd.in/dGUH9v79. Despite our confidence that the project and its approach are no longer current, there remains significant interest in this source code, with thousands of mentions across the internet.

At the GitHub repository, you’ll find not only the source code and build instructions but also pre-built binaries, demonstration, and references to the original contributors.