2026-05-10 09:41:33 -04:00
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# Real-time H.264 recording
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The default recorder (`RawBgraRecorderSink`) writes uncompressed BGRA to disk
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and ships a `convert.cmd` for post-recording FFmpeg encoding. That's safe
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(no extra dependencies, works without an encoder installed) but disk-heavy:
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1080p60 = ~500 MB/s, 720p30 = ~88 MB/s.
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For long shows or operators on slower disks, the engine ships a
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**`MediaFoundationRecorderSink`** that encodes to H.264 in real time using
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Windows Media Foundation. Inline encoding cuts disk pressure ~10× and
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produces a finished `.mp4` without the convert step.
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It's behind a build flag because activating it requires adding a NuGet
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dependency. The structural code is already in
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`src/TeamsISO.Engine/Pipeline/MediaFoundationRecorderSink.cs`.
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2026-05-10 20:39:23 -04:00
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## Status — May 2026
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**Activation deferred.** The Vortice.MediaFoundation 3.6.2 NuGet package
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is referenced from `TeamsISO.Engine.csproj`, but the `MF_AVAILABLE` symbol
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is *not* defined. The scaffold in
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`src/TeamsISO.Engine/Pipeline/MediaFoundationRecorderSink.cs` was written
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against an older Vortice API and needs a port pass before activation:
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- `MFVersion` → not on `MediaFactory` in 3.6.2; pass the SDK version
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directly to `MFStartup`.
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- `MediaFactory.MF_LOW_LATENCY` → relocated to a different attribute
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constants class.
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- `IMFAttributes.SetUINT32` → replaced with a generic `Set` overload.
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- `IMFMediaType.MajorType` / `.SubType` / `.AvgBitrate` properties
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→ now use `SetGUID(MFAttributeKeys.MajorType, ...)` etc.
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- `VideoFormatGuids.RGB32` → renamed (likely `Rgb32`).
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- `IMFMediaBuffer.Lock(out IntPtr, out int, out int)` → explicit out-param
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signature, no longer returns a locked-buffer wrapper.
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- `IMFSinkWriter.Finalize_` → renamed (likely `Finalize`).
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Until the port lands, the `RawBgraRecorderSink` is the only IRecorderSink
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production uses. The raw recorder is reliable and FFmpeg post-processing
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via the emitted `convert.cmd` produces equivalent .mp4s; you just pay the
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disk pressure during the show.
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## Activating it (after the port)
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1. **Update the scaffold** to match Vortice 3.6.2's API surface. A clean
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reference implementation lives in the Vortice samples repo under
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`samples/MediaFoundationSamples`.
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2026-05-10 09:41:33 -04:00
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2. **Define the `MF_AVAILABLE` build symbol** in `TeamsISO.Engine.csproj`:
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```xml
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<PropertyGroup>
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<DefineConstants>$(DefineConstants);MF_AVAILABLE</DefineConstants>
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</PropertyGroup>
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```
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3. **Swap the recorder factory** in `IsoController.EnableIsoAsync`:
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```csharp
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// Old:
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recorder = new RawBgraRecorderSink(_loggerFactory.CreateLogger<RawBgraRecorderSink>());
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// New:
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recorder = new MediaFoundationRecorderSink(_loggerFactory.CreateLogger<MediaFoundationRecorderSink>());
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```
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Both classes implement `IRecorderSink` so the rest of the pipeline is
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unchanged.
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4. **Build and smoke-test.** Existing unit tests don't touch the recorder;
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the integration tier covers it once you've enabled MF.
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## What the MF recorder produces
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For each enabled ISO with recording on:
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- `<recordings>/<participant>/output.mp4` — H.264 video at the engine's
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configured resolution / framerate, target bitrate ~0.07 bits/pixel
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(~7 Mbps for 1080p30, ~3 Mbps for 720p30).
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- `<recordings>/<participant>/markers.txt` — tab-separated marker offsets
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from `IIsoController.AddRecordingMarker`. Manually chapter the .mp4 with
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`mp4chaps -c -i markers.txt output.mp4` (mp4chaps from the `mp4v2` tools).
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## Trade-offs vs. RawBgraRecorderSink
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| | Raw BGRA | Media Foundation H.264 |
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| --------------------- | --------------- | ---------------------- |
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| Dependencies | None | Vortice.MediaFoundation NuGet |
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| Disk @ 1080p60 | ~500 MB/s | ~50 MB/s |
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| Disk @ 720p30 | ~88 MB/s | ~9 MB/s |
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| CPU | Negligible | Moderate (inline encode) |
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| Output | `.bgra` + `convert.cmd` for FFmpeg post-pass | Finished `.mp4` |
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| Markers in container | No (sidecar JSON) | Sidecar `.txt`, chapter via mp4chaps |
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| Reliable on legacy GPUs | Yes | Yes (MF falls back to software encoder if no hw H.264) |
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If your target machines have NVIDIA NVENC / Intel QuickSync, MF will use
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the hardware encoder transparently — that's the path that gives you
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multi-stream realtime H.264 with low CPU.
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