cap-camera-directshow

Ergonomic Rust wrapper around Windows DirectShow API for legacy camera capture, providing safe abstractions over COM interfaces while maintaining compatibility with older camera devices and drivers that don't support Media Foundation. Aims to mirror how Chromium consumes DirectShow.

Purpose

Provides safe access to Windows camera devices through DirectShow's filter graph architecture, handling COM initialization, device enumeration through monikers, format negotiation via IAMStreamConfig, and synchronous frame delivery through custom sink filters.

Key Features

• Device Discovery: VideoInputDeviceIterator for enumerating video capture devices via COM monikers
• Format Enumeration: Access to AM_MEDIA_TYPE formats and frame rates through IAMStreamConfig
• Synchronous Capture: Callback-based frame delivery via custom SinkFilter implementation
• Memory Safety: RAII COM object management with automatic cleanup and proper reference counting
• Legacy Support: Compatibility with older cameras that lack Media Foundation support
• Video Format Support: Built-in support for I420, RGB24, YUY2, MJPG, NV12, and other common formats

Core APIs

Device Management

• initialize_directshow() - Initialize DirectShow COM subsystem
• VideoInputDeviceIterator::new() - Enumerate available cameras via system device enumerator
• VideoInputDevice::name(), VideoInputDevice::id(), VideoInputDevice::model_id() - Device metadata
• VideoInputDevice::media_types() - Iterator over supported AMMediaType formats

Capture Pipeline

• VideoInputDevice::start_capturing(format, callback) - Begin sync capture with specified format
• CaptureHandle::stop_capturing() - Stop capture session and disconnect filter graph
• SinkCallback - Frame processing callback receiving IMediaSample and media type

Format Processing

• AMMediaType - Safe wrapper around AM_MEDIA_TYPE with automatic memory management
• AM_MEDIA_TYPEExt::subtype_str() - Convert format GUIDs to readable strings
• AM_MEDIA_TYPEVideoExt::video_info() - Access video format details and dimensions

Filter Graph Extensions

• IBaseFilterExt::get_pin() - Find pins by direction, category, and media type
• IAMStreamConfigExt::media_types() - Enumerate supported capture formats
• IPinExt::matches_category() - Pin category matching for capture pin discovery

Architecture

Bridges DirectShow's COM-based filter graph model to Rust's ownership system using custom sink filter implementation, RAII for COM resource management, and comprehensive trait extensions for ergonomic API access. Designed for maximum compatibility with legacy camera hardware while maintaining memory safety.

Error Handling

Comprehensive StartCapturingError enum covering:

• NoInputPin - Sink filter pin creation failures
• CreateGraph - Filter graph builder instantiation errors
• ConfigureGraph - Filter connection and configuration issues
• Run - Media control execution failures
• Other - General DirectShow COM errors

The crate provides robust error propagation while maintaining the callback-based architecture required for real-time video capture scenarios.