iOS的音视频框架有 AVKit 和 AVFoundation，他们的关系如图：
可以看出，avkit 位于相对上层，使用起来也更加容易，我们先讲解 avkit。
AVKit
苹果官方文档在这里：https://developer.apple.com/documentation/avkit/playing-video-content-in-a-standard-user-interface
架构
+------------------------------------------------------------------+
| Application Layer |
| (Your App / SwiftUI / UIKit) |
| |
| - Custom Video Player UI |
| - Playback Controls, Seek Bar, Buffer Indicator |
| - Business Logic (e.g., DRM, Analytics, Playlist) |
+-------------------------------+----------------------------------+
|
| Uses
\/
+------------------------------------------------------------------+
| High-Level AV Frameworks |
| (Built on top of AVFoundation) |
| |
| +----------------+ +------------------+ +--------------+ |
| | AVKit | | ReplayKit | | Photos | |
| | (AVPlayerView, | | (Screen/Video | | (PHImage | |
| | AVRoutePicker)| | Recording) | | Manager) | |
| +----------------+ +------------------+ +--------------+ |
| |
| * Provides ready-to-use UI components |
| * Simplifies common media tasks |
+-------------------------------+----------------------------------+
|
| Built upon
\/
+------------------------------------------------------------------+
| AVFoundation Core |
| (The main multimedia framework on Apple platforms) |
| |
| +------------------------------------------------------------+ |
| | AVPlayer / AVQueuePlayer | |
| | - Controls playback timeline | |
| +------------------------------------------------------------+ |
| |
| +------------------------------------------------------------+ |
| | AVPlayerItem | |
| | - Represents a single media asset (video/audio) | |
| | - Manages loading, buffering, tracks, metadata | |
| +------------------------------------------------------------+ |
| |
| +------------------------------------------------------------+ |
| | AVAsset / AVURLAsset / AVComposition | |
| | - Describes media structure (tracks, duration, format) | |
| | - Does NOT load data until needed (lazy) | |
| +------------------------------------------------------------+ |
| |
| +------------------------------------------------------------+ |
| | AVMetadata, AVTimedMetadataGroup | |
| | - Handles subtitles, ID3 tags, chapter info | |
| +------------------------------------------------------------+ |
| |
| +------------------------------------------------------------+ |
| | AVCaptureSession / AVCaptureDevice | |
| | - Camera & microphone input pipeline | |
| +------------------------------------------------------------+ |
| |
| +------------------------------------------------------------+ |
| | AVAssetExportSession / AVAssetReader/Writer | |
| | - Transcoding, trimming, mixing | |
| +------------------------------------------------------------+ |
+-------------------------------+----------------------------------+
|
| Relies on
\/
+------------------------------------------------------------------+
| Lower-Level C Frameworks |
| (Private or semi-private; mostly closed-source) |
| |
| +----------------+ +----------------+ +----------------+ |
| | Core Media | | Core Video | | Core Audio | |
| | (CMTime, | | (CVPixelBuffer,| | (AudioStream, | |
| | CMSampleBuffer)| | CVImageBuffer)| | AudioQueue) | |
| +----------------+ +----------------+ +----------------+ |
| |
| +----------------+ +----------------+ +----------------+ |
| | Video Toolbox | | Audio Toolbox | | MediaToolbox | |
| | (HW encoding/ | | (Audio codecs) | | (Playback | |
| | decoding) | | | | engine) | |
| +----------------+ +----------------+ +----------------+ |
| |
| +------------------------------------------------------------+ |
| | Network Stack (NSURLSession, HTTP Live Streaming parser) | |
| +------------------------------------------------------------+ |
+-------------------------------+----------------------------------+
|
| Runs on
\/
+------------------------------------------------------------------+
| Hardware & OS Kernel |
| |
| - GPU (for video decode/encode via Metal/VDA) |
| - Audio I/O (via HAL - Hardware Abstraction Layer) |
| - File System / Network Interface |
| - Secure Enclave (for FairPlay DRM) |
+------------------------------------------------------------------+
应用层开发，我们一般接触到的：
+--------------------------------------------------+
| Your App |
| |
| +----------------+ +---------------------+ |
| | Custom Player | | Game / Tutorial App | |
| | (Uses AVFoun- | | (Uses ReplayKit to | |
| | dation directly)| | record screen) | |
| +----------------+ +----------+----------+ |
| | |
+------------------+-----------------+-------------+
| |
| Uses | Uses
\/ \/
+----------+------+ +-------+--------+
| AVKit | | ReplayKit |
| (For standard | | (For recording |
| playback UI) | | and broadcast)|
+--------+--------+ +-------+--------+
| |
| Both rely on | Relies on
\/ \/
+--------------------------------------+
| AVFoundation |
| - AVPlayer (playback) |
| - AVCaptureSession (audio input) |
| - AVAssetWriter (recording output) |
| - AVAsset (media representation) |
+--------------------------------------+
|
| Uses
\/
+---------------------+
| Core Media / Video |
| Toolbox / Core Audio|
+---------------------+总结
大多数 App 会混合使用：
用 AVFoundation 做核心播放逻辑
用 AVKit 做全屏播放页
用 ReplayKit 做用户生成内容（UGC）录制
ijkplayer
avfoundation 是 iOS 自带，免去了编译操作，但是定制性差一些，下面聊聊比较火的 ijkplayer。他的架构图：
+------------------------------------------------------------------+
| Application Layer |
| (Your App / Demo: IJKMediaDemo, Custom Player UI) |
+------------------------------------------------------------------+
│
\/
+------------------------------------------------------------------+
| IJKMediaPlayback API Layer |
| - Protocol: IJKMediaPlayback (Obj-C) |
| - Main Class: IJKFFMoviePlayerController |
| - View: IJKFFMovieView (Metal/OpenGL) |
+------------------------------------------------------------------+
│
\/
+------------------------------------------------------------------+
| FFmpeg Wrapper Layer (C) |
| - ijkavformat.c / ijkio.c / ijkplayer.c |
| - 封装 FFmpeg 核心功能：demux, decode, audio output, clock sync |
| - 提供 C 接口：ijkmp_* (e.g., ijkmp_prepare_async) |
+------------------------------------------------------------------+
│
┌──────────────────┼──────────────────┐
\/ \/ \/
+------------------+ +------------------+ +------------------+
| libavformat | | libavcodec | | libswscale |
| (Demuxing) | | (Decoding) | | (Scaling/YUV) |
+------------------+ +------------------+ +------------------+
│ │ │
\/ \/ \/
+---------------------------------------------------------------+
| libavutil (Utils) |
| - dict, log, thread, time, frame, hwaccel (VideoToolbox) |
+---------------------------------------------------------------+
│
\/
+------------------------------------------------------------------+
| Optional Dependencies |
| - OpenSSL (libcrypto/libssl): for HTTPS/RTMPS |
| - zlib: for HTTP gzip |
| - VideoToolbox: for iOS hardware decoding (H.264/H.265) |
+------------------------------------------------------------------+
行动
下载编译运行都可以在这里找到：ijkplayer iOS 编译完全指南（Xcode 26.0.1 下，修复部分问题）
对比
优劣势：
+------------------+----------------+-------------------+------------------------+-----------+--------------+
| 特性 | ijkplayer | AVPlayer (iOS) | ExoPlayer (Android) | WebRTC | GStreamer |
+------------------+----------------+-------------------+------------------------+-----------+--------------+
| RTMP 支持 | ✅ 原生 | ❌ 不支持 | ❌ 需扩展 | ❌ 不支持 | ✅ 插件支持 |
+------------------+----------------+-------------------+------------------------+-----------+--------------+
| HTTP-FLV 支持 | ✅ 原生 | ❌ | ❌ | ❌ | ✅ |
+------------------+----------------+-------------------+------------------------+-----------+--------------+
| HLS 延迟 | ~3~8s（可优化）| 6~15s（固定） | ~3~8s（可优化） | ❌ | ~2~5s |
+------------------+----------------+-------------------+------------------------+-----------+--------------+
| 最低延迟 | 1~3s | ≥6s | 2~5s | <500ms | 1~3s |
+------------------+----------------+-------------------+------------------------+-----------+--------------+
| 硬解支持 | ✅ (VideoToolbox)| ✅ | ✅ | ✅ | ✅ (需配置) |
+------------------+----------------+-------------------+------------------------+-----------+--------------+
| 自定义协议 | ✅ (C 层 IO) | ❌ | ✅ (DataSource) | ❌ | ✅ |
+------------------+----------------+-------------------+------------------------+-----------+--------------+
| 包体积增量 | +8~12 MB | 0 | +5~8 MB | +10~15 MB | +15~20 MB |
+------------------+----------------+-------------------+------------------------+-----------+--------------+
| 开发难度 | 中（需编译） | 低 | 中 | 高 | 高 |
+------------------+----------------+-------------------+------------------------+-----------+--------------+
| 适用场景 | 移动端直播 | 点播/HLS | Android 直播 | 超低延迟 | 嵌入式/专业 |
| | (RTMP/FLV) | | | 互动 | |
+------------------+----------------+-------------------+------------------------+-----------+--------------+
ijkplayer 直播模块介绍
架构
[RTMP Server / HTTP-FLV CDN]
│
▼
Custom I/O (ijkio.c) ←──┐
│ │ 支持自定义协议、重连、超时
libavformat (demux) │
│ │ 绕过 FFmpeg 默认缓冲
AVPacket → PacketQueue ─┘
│
libavcodec (decode)
│
AVFrame → FrameQueue
│
VideoToolbox (硬解) or libswscale (软解)
│
Metal / OpenGL → IJKFFMovieView
│
AudioQueue → Speaker编译配置
# module.sh
export COMMON_FF_CFG_FLAGS="$COMMON_FF_CFG_FLAGS --enable-protocol=rtp"
export COMMON_FF_CFG_FLAGS="$COMMON_FF_CFG_FLAGS --enable-protocol=rtmp"
export COMMON_FF_CFG_FLAGS="$COMMON_FF_FLAGS --extra-cflags=-I${FFMPEG_DEP_ROOT}/include"初始化
NSURL *url = [NSURL URLWithString:@"rtmp://live.example.com/app/stream"];
IJKFFOptions *options = [IJKFFOptions optionsByDefault];
// 核心：低延迟配置
[options setPlayerOptionIntValue:1 forKey:@"videotoolbox"]; // 硬解
[options setPlayerOptionIntValue:1 forKey:@"start_on_prepared"]; // 准备好就播
[options setPlayerOptionIntValue:1 forKey:@"overlay-format"]; // GPU 渲染
// 减少缓冲（直播关键！）
[options setFormatOptionStringValue:@"0" forKey:@"reconnect"];
[options setFormatOptionStringValue:@"5000000" forKey:@"timeout"]; // 5s 超时
[options setFormatOptionStringValue:@"nobuffer" forKey:@"fflags"];
[options setFormatOptionStringValue:@"1" forKey:@"flush_packets"];
[options setCodecOptionStringValue:@"low_delay" forKey:@"flags"];
[options setPlayerOptionIntValue:1 forKey:@"framedrop"]; // 丢帧保流畅
IJKFFMoviePlayerController *player = [[IJKFFMoviePlayerController alloc] initWithContentURL:url options:options];