cap-media-info

A Rust crate providing information structures for audio and video processing, designed to bridge FFmpeg and CPAL libraries for media capture and encoding applications.

Overview

This crate defines core data structures (AudioInfo and VideoInfo) that encapsulate media stream parameters and provide utilities for converting between different media processing libraries. It's particularly useful for applications that need to capture audio/video data and encode it using FFmpeg.

Core Structures

AudioInfo

Represents audio stream parameters and provides conversion utilities between CPAL (Cross-Platform Audio Library) and FFmpeg formats.

Fields:

• sample_format: FFmpeg sample format
• sample_rate: Audio sample rate in Hz
• channels: Number of audio channels (currently limited to 1-2)
• time_base: FFmpeg time base for timestamps
• buffer_size: Audio buffer size in samples

Key Methods:

• new(): Create with basic parameters and validation
• from_stream_config(): Create from CPAL's SupportedStreamConfig
• from_decoder(): Create from FFmpeg's audio decoder
• empty_frame(): Generate empty audio frames
• wrap_frame(): Wrap raw audio data into FFmpeg frames with automatic deinterleaving

Limitations:

• Currently supports only mono (1) and stereo (2) channel configurations
• Maximum channels defined by MAX_AUDIO_CHANNELS = 2

VideoInfo

Represents video stream parameters for various pixel formats and provides frame manipulation utilities.

Fields:

• pixel_format: FFmpeg pixel format
• width: Video width in pixels
• height: Video height in pixels
• time_base: FFmpeg time base for timestamps
• frame_rate: Video frame rate

Key Methods:

• from_raw(): Create from RawVideoFormat enum
• from_raw_ffmpeg(): Create directly from FFmpeg pixel format
• scaled(): Create scaled version with proportional resizing
• wrap_frame(): Wrap raw video data into FFmpeg frames with stride handling

RawVideoFormat

Enum mapping common video formats to FFmpeg pixel formats:

• Bgra → BGRA
• Mjpeg → YUVJ422P
• Uyvy → UYVY422
• RawRgb → RGB24
• Nv12 → NV12
• Gray → GRAY8
• YUYV420 → YUV420P
• Rgba → RGBA

Additional Features

PlanarData Trait

Provides safe access to planar audio data, fixing issues with FFmpeg's audio frame data access for multi-channel audio processing.

Error Handling

• AudioInfoError: Handles validation errors, particularly for unsupported channel configurations

Dependencies

• ffmpeg: Core FFmpeg bindings for media processing
• cpal: Cross-platform audio library for audio I/O
• thiserror: Error handling utilities

Use Cases

This crate is designed for applications that need to:

• Capture audio from system devices using CPAL
• Capture video from various sources
• Convert raw media data to FFmpeg-compatible formats
• Encode captured media using FFmpeg codecs
• Handle format conversions between different media libraries

Integration

The crate serves as a compatibility layer between:

• CPAL for audio input/output operations
• FFmpeg for media encoding/decoding operations
• Raw media data processing pipelines

This makes it particularly suitable for screen recording, video conferencing, and media streaming applications.