ffmpeg-API划分

本系列根据ffmpeg api文档进行介绍，
ffmpeg 文档描述大概可以分为以下几个不同的库:

库	描述
libavcodec	音视频各种格式的编解码。各种格式的编解码代码(如aacenc.c、aacdec.c等)
libavformat	用于各种音视频封装格式的生成和解析，包括获取解码所需信息、读取音视频数据等功能。各种流媒体协议代码(如rtmpproto.c等)以及音视频格式的(解)复用代码(如flvdec.c、flvenc.c等)
libavutil	包含一些公共的工具函数的使用库，包括算数运算，字符操作等
libavfilter	各种音视频过滤器
libavdevice	用于硬件的音视频采集、加速和显示
libswresample	提供音频重采样，采样格式转换和混合等功能
libswscale	提供原始视频的比例缩放、色彩映射转换、图像颜色空间或格式转换的功能

模块划分

按官方的文档，ffmpeg 库按模块划分为，

ASS styles
ASS functions
end of Dialogue Event
libpostproc Video 后处理库
libswresample Audio 重采样, 采样格式转换以及混合库
libswscale 颜色转换和缩放库
VDPAU_Decoding

其他比较大的模块主要在，libavcodec, libavformat, libavutil

libavcodec 模块

libavcodec: 编码解码库
- Decoding
  - Frame 解析
- Encoding
- Codecs
  - Native Codecs
  - External library wrappers
  - Hardware Accelerators bridge
    - oDirect3D11
    - oDXVA2
    - oVA API Decoding
    - oVDPAU Decoder and Renderer: VDPAU硬件加速有两个模块
    - XvMC
- Internal
- send/receive encoding and decoding API overview: avcodec_send_packet()/avcodec_receive_frame()/avcodec_send_frame()/ avcodec_receive_packet() 函数提供一个编解码 API, 将输入和输出分离开
- Core functions/structures:基本定义、查询 libavcodec 功能、关键结构体内崔分配，等等
  - AVPacket: 编码的数据单元
  - AVHWAccel:
  - AVPicture: Picture 数据结构体
- Utility functions:与编码和解码（或两者都不是）相关的其他实用函数
  - Pixel formats: Pixel 格式相关的函数
  - FFT functions
    libavdevice
libavdevice: 指定设备的 muxing/demuxing 库

libavfilter

libavfilter: Graph-based 帧编辑库
- Buffer sink API
  - Buffer sink accessors: 获取 stream 的属性
- Buffer source API

libavformat

libavformat: I/O 和分解/复用库
- Demuxing: Demuxers 读取一个媒体文件，分离到 packets
- Muxing: muxer 以 AVPackets 的形式获取编码数据，并将其写入文件或指定容器格式的其他 bytestreams 输出流.
- I/O Read/Write
- Demuxers
  - Native Demuxers
  - External library wrappers
- I/O Protocols
- Internal
- Public Metadata API: 分解时，该 API 允许 libavformat 导出 metadata tags 给 application客户端
- Core functions: 查询 libavformat capabilities 函数, 核心结构体内存分配
- Utility functions: 与复用和解复用相关的杂项效用函数（或两者都不）
  - RIFF FourCCs: 获取将 RIFF FourCCs 映射到 libavcodec AVCodecIDs 的表

libavresample

libavresample Libavresample (lavr) is a library that handles audio resampling, sample format conversion and mixing

libavutil

libavutil Common code shared across all FFmpeg libraries
- Crypto and Hashing
  - AES
  - Base64
  - Blowfish
  - CAMELLIA
  - CAST5
  - DES
  - Hash Functions: Hash functions useful in multimedia
    - Adler-32：Adler-32 hash function implementation
    - CRC：CRC (Cyclic Redundancy Check) hash function implementation
    - Generic Hashing API：An abstraction layer for all hash functions supported by libavutil
    - MD5：MD5 hash function implementation
    - Murmur3：MurmurHash3 hash function implementation
    - RIPEMD：RIPEMD hash function implementation
    - SHA：SHA-1 and SHA-256 (Secure Hash Algorithm) hash function implementations
    - SHA-512：SHA-512 (Secure Hash Algorithm) hash function implementations
  - HMAC
  - LZO
  - RC4
  - TEA
  - TWOFISH
  - XTEA
- Mathematics：时间和时间戳的数据工具集
  - AVRational：Rational number calculation
- String Manipulation：字符操作
- Memory Management：操作内存的工具集
  - Alignment Macros：宏指令工具函数
  - Function Attributes： Function attributes applicable to memory handling functions
  - Heap Management Functions responsible for allocating, freeing, and copying memory
  - Dynamic Array Utilities to make an array grow when needed
  - Miscellaneous Functions Other functions related to memory allocation
- Data Structures
  - AVBuffer AVBuffer is an API for reference-counted data buffers
  - AVBufferPool AVBufferPool is an API for a lock-free thread-safe pool of AVBuffers
  - AVFrame AVFrame is an abstraction for reference-counted raw multimedia data
    - AV_FRAME_FLAGS Flags describing additional frame properties
  - AVOptions AVOptions provide a generic system to declare options on arbitrary structs (“objects”)
    - Evaluating option strings This group of functions can be used to evaluate option strings and get numbers out of them
    - Option setting functions Those functions set the field of obj with the given name to value
    - Option getting functions Those functions get a value of the option with the given name from an object
  - AVDictionary Simple key:value store
  - AVTree Low-complexity tree container
- Video related
  - Display transformation matrix functions The display transformation matrix specifies an affine transformation that should be applied to video frames for correct presentation
  - Spherical video mapping A spherical video file contains surfaces that need to be mapped onto a sphere
  - Stereo3D types and functions A stereoscopic video file consists in multiple views embedded in a single frame, usually describing two views of a scene
- Audio related
  - Audio FIFO Buffer
  - Audio channel masks A channel layout is a 64-bits integer with a bit set for every channel
  - Audio channel layouts
  - Audio downmix metadata
  - Audio sample formats Audio sample format enumeration and related convenience functions
  - Samples manipulation Functions that manipulate audio samples
- Error Codes
- Logging Facility
  - Logging Constants
- Other
  - Preprocessor String Macros String manipulation macros
  - Library Version Macros Useful to check and match library version in order to maintain backward compatibility
  - Constants
    - Encoding specific
    - Timestamp specific FFmpeg internal timebase and timestamp definitions
  - Image related AVPicture types, pixel formats and basic image planes manipulation
  - Version and Build diagnostics Macros and function useful to check at compiletime and at runtime which version of libavutil is in use
    - Deprecation Guards FF_API_* defines may be placed below to indicate public API that will be dropped at a future version bump
  - Media Type Media Type

参考:
http://ffmpeg.org/doxygen/4.1/modules.html

模块划分

libavcodec 模块

libavdevice

libavfilter

libavformat

libavresample

libavutil