ffdshow 源代码分析 6： 对解码器的dll的封装（libavcodec）

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ffdshow源代码分析系列文章列表：

ffdshow 源代码分析 1： 整体结构

ffdshow 源代码分析 2： 位图覆盖滤镜（对话框部分Dialog）

ffdshow 源代码分析 3： 位图覆盖滤镜（设置部分Settings）

ffdshow 源代码分析 4： 位图覆盖滤镜（滤镜部分Filter）

ffdshow 源代码分析 5： 位图覆盖滤镜（总结）

ffdshow 源代码分析 6： 对解码器的dll的封装（libavcodec）

ffdshow 源代码分析 7： libavcodec视频解码器类（TvideoCodecLibavcodec）

ffdshow 源代码分析 8： 视频解码器类（TvideoCodecDec）

ffdshow 源代码分析 9： 编解码器有关类的总结

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ffdshow封装了多个视音频解码器，比如libmpeg2，libavcodec，xvid等等。其中最重要的是libavcodec，这个是ffmpeg提供的解码器，在ffdshow中起到了“挑大梁”的作用。本文分析ffdshow对解码器的封装方式，就以libavcodec为例。

在ffdshow中，libavcodec的被封装在ffmpeg.dll文件中，通过加载该dll中的函数，就可以使用libavcodec的各种方法。

Ffmpeg对libavcodec的封装类的定义位于codecs->libavcodec->Tlibavcodec.h。实现则位于codecs->libavcodec->Tlibavcodec.cpp。

先来看一看Tlibavcodec.h：

/*
*雷霄骅
*leixiaohua1020@126.com
*中国传媒大学/数字电视技术
*/
#ifndef _TLIBAVCODEC_H_
#define _TLIBAVCODEC_H_
//将FFmpeg的Dll中的方法封装到一个类中，以供使用
#include "../codecs/ffcodecs.h"
#include <dxva.h>
#include "TpostprocSettings.h"
#include "ffImgfmt.h"
#include "libavfilter/vf_yadif.h"
#include "libavfilter/gradfun.h"
#include "libswscale/swscale.h"

struct AVCodecContext;
struct AVCodec;
struct AVFrame;
struct AVPacket;
struct AVCodecParserContext;
struct SwsContext;
struct SwsParams;
struct PPMode;
struct AVDictionary;

struct Tconfig;
class Tdll;
struct DSPContext;
struct TlibavcodecExt;
//封装FFMPEG
//里面的函数基本上是FFMPEG的API
struct Tlibavcodec {
private:
int (*libswscale_sws_scale)(struct SwsContext *context, const uint8_t* const srcSlice[], const int srcStride[],
int srcSliceY, int srcSliceH, uint8_t* const dst[], const int dstStride[]);
//加载DLL的类
Tdll *dll;
int refcount;
static int get_buffer(AVCodecContext *c, AVFrame *pic);
CCritSec csOpenClose;
public:
Tlibavcodec(const Tconfig *config);
~Tlibavcodec();
static void avlog(AVCodecContext*, int, const char*, va_list);
static void avlogMsgBox(AVCodecContext*, int, const char*, va_list);
void AddRef(void) {
refcount++;
}
void Release(void) {
if (--refcount < 0) {
delete this;
}
}
static bool getVersion(const Tconfig *config, ffstring &vers, ffstring &license);
static bool check(const Tconfig *config);
static int ppCpuCaps(uint64_t csp);
static void pp_mode_defaults(PPMode &ppMode);
static int getPPmode(const TpostprocSettings *cfg, int currentq);
static void swsInitParams(SwsParams *params, int resizeMethod);
static void swsInitParams(SwsParams *params, int resizeMethod, int flags);

bool ok;
AVCodecContext* avcodec_alloc_context(AVCodec *codec, TlibavcodecExt *ext = NULL);

void (*avcodec_register_all)(void);
AVCodecContext* (*avcodec_alloc_context0)(AVCodec *codec);
AVCodec* (*avcodec_find_decoder)(AVCodecID codecId);
AVCodec* (*avcodec_find_encoder)(AVCodecID id);
int (*avcodec_open0)(AVCodecContext *avctx, AVCodec *codec, AVDictionary **options);
int  avcodec_open(AVCodecContext *avctx, AVCodec *codec);
AVFrame* (*avcodec_alloc_frame)(void);
int (*avcodec_decode_video2)(AVCodecContext *avctx, AVFrame *picture,
int *got_picture_ptr,
AVPacket *avpkt);
int (*avcodec_decode_audio3)(AVCodecContext *avctx, int16_t *samples,
int *frame_size_ptr,
AVPacket *avpkt);
int (*avcodec_encode_video)(AVCodecContext *avctx, uint8_t *buf, int buf_size, const AVFrame *pict);
int (*avcodec_encode_audio)(AVCodecContext *avctx, uint8_t *buf, int buf_size, const short *samples);
void (*avcodec_flush_buffers)(AVCodecContext *avctx);
int (*avcodec_close0)(AVCodecContext *avctx);
int  avcodec_close(AVCodecContext *avctx);

void (*av_log_set_callback)(void (*)(AVCodecContext*, int, const char*, va_list));
void* (*av_log_get_callback)(void);
int (*av_log_get_level)(void);
void (*av_log_set_level)(int);

void (*av_set_cpu_flags_mask)(int mask);

int (*avcodec_default_get_buffer)(AVCodecContext *s, AVFrame *pic);
void (*avcodec_default_release_buffer)(AVCodecContext *s, AVFrame *pic);
int (*avcodec_default_reget_buffer)(AVCodecContext *s, AVFrame *pic);
const char* (*avcodec_get_current_idct)(AVCodecContext *avctx);
void (*avcodec_get_encoder_info)(AVCodecContext *avctx, int *xvid_build, int *divx_version, int *divx_build, int *lavc_build);

void* (*av_mallocz)(size_t size);
void (*av_free)(void *ptr);

AVCodecParserContext* (*av_parser_init)(int codec_id);
int (*av_parser_parse2)(AVCodecParserContext *s, AVCodecContext *avctx, uint8_t **poutbuf, int *poutbuf_size, const uint8_t *buf, int buf_size, int64_t pts, int64_t dts, int64_t pos);
void (*av_parser_close)(AVCodecParserContext *s);

void (*av_init_packet)(AVPacket *pkt);
uint8_t* (*av_packet_new_side_data)(AVPacket *pkt, enum AVPacketSideDataType type, int size);

int (*avcodec_h264_search_recovery_point)(AVCodecContext *avctx,
const uint8_t *buf, int buf_size, int *recovery_frame_cnt);

static const char_t *idctNames[], *errorRecognitions[], *errorConcealments[];
struct Tdia_size {
int size;
const char_t *descr;
};
static const Tdia_size dia_sizes[];

//libswscale imports
SwsContext* (*sws_getCachedContext)(struct SwsContext *context, int srcW, int srcH, enum PixelFormat srcFormat,
int dstW, int dstH, enum PixelFormat dstFormat, int flags,
SwsFilter *srcFilter, SwsFilter *dstFilter, const double *param, SwsParams *ffdshow_params);

void (*sws_freeContext)(SwsContext *c);
SwsFilter* (*sws_getDefaultFilter)(float lumaGBlur, float chromaGBlur,
float lumaSharpen, float chromaSharpen,
float chromaHShift, float chromaVShift,
int verbose);
void (*sws_freeFilter)(SwsFilter *filter);
int sws_scale(struct SwsContext *context, const uint8_t* const srcSlice[], const stride_t srcStride[],
int srcSliceY, int srcSliceH, uint8_t* const dst[], const stride_t dstStride[]);
SwsVector *(*sws_getConstVec)(double c, int length);
SwsVector *(*sws_getGaussianVec)(double variance, double quality);
void (*sws_normalizeVec)(SwsVector *a, double height);
void (*sws_freeVec)(SwsVector *a);
int (*sws_setColorspaceDetails)(struct SwsContext *c, const int inv_table[4],
int srcRange, const int table[4], int dstRange,
int brightness, int contrast, int saturation);
const int* (*sws_getCoefficients)(int colorspace);

int (*GetCPUCount)(void);

//libpostproc imports
void (*pp_postprocess)(const uint8_t * src[3], const stride_t srcStride[3],
uint8_t * dst[3], const stride_t dstStride[3],
int horizontalSize, int verticalSize,
const /*QP_STORE_T*/int8_t *QP_store,  int QP_stride,
/*pp_mode*/void *mode, /*pp_context*/void *ppContext, int pict_type);
/*pp_context*/
void *(*pp_get_context)(int width, int height, int flags);
void (*pp_free_context)(/*pp_context*/void *ppContext);
void (*ff_simple_idct_mmx)(int16_t *block);

// DXVA imports
int (*av_h264_decode_frame)(struct AVCodecContext* avctx, uint8_t *buf, int buf_size);
int (*av_vc1_decode_frame)(struct AVCodecContext* avctx, uint8_t *buf, int buf_size);

// === H264 functions
int (*FFH264CheckCompatibility)(int nWidth, int nHeight, struct AVCodecContext* pAVCtx, BYTE* pBuffer, UINT nSize, int nPCIVendor, int nPCIDevice, LARGE_INTEGER VideoDriverVersion);
int (*FFH264DecodeBuffer)(struct AVCodecContext* pAVCtx, BYTE* pBuffer, UINT nSize, int* pFramePOC, int* pOutPOC, REFERENCE_TIME* pOutrtStart);
HRESULT(*FFH264BuildPicParams)(DXVA_PicParams_H264* pDXVAPicParams, DXVA_Qmatrix_H264* pDXVAScalingMatrix, int* nFieldType, int* nSliceType, struct AVCodecContext* pAVCtx, int nPCIVendor);

void (*FFH264SetCurrentPicture)(int nIndex, DXVA_PicParams_H264* pDXVAPicParams, struct AVCodecContext* pAVCtx);
void (*FFH264UpdateRefFramesList)(DXVA_PicParams_H264* pDXVAPicParams, struct AVCodecContext* pAVCtx);
BOOL (*FFH264IsRefFrameInUse)(int nFrameNum, struct AVCodecContext* pAVCtx);
void (*FF264UpdateRefFrameSliceLong)(DXVA_PicParams_H264* pDXVAPicParams, DXVA_Slice_H264_Long* pSlice, struct AVCodecContext* pAVCtx);
void (*FFH264SetDxvaSliceLong)(struct AVCodecContext* pAVCtx, void* pSliceLong);

// === VC1 functions
HRESULT(*FFVC1UpdatePictureParam)(DXVA_PictureParameters* pPicParams, struct AVCodecContext* pAVCtx, int* nFieldType, int* nSliceType, BYTE* pBuffer, UINT nSize, UINT* nFrameSize, BOOL b_SecondField, BOOL* b_repeat_pict);
int (*FFIsSkipped)(struct AVCodecContext* pAVCtx);

// === Common functions
char*    (*GetFFMpegPictureType)(int nType);
unsigned long(*FFGetMBNumber)(struct AVCodecContext* pAVCtx);

// yadif
void (*yadif_init)(YADIFContext *yadctx);
void (*yadif_uninit)(YADIFContext *yadctx);
void (*yadif_filter)(YADIFContext *yadctx, uint8_t *dst[3], stride_t dst_stride[3], int width, int height, int parity, int tff);

// gradfun
int (*gradfunInit)(GradFunContext *ctx, const char *args, void *opaque);
void (*gradfunFilter)(GradFunContext *ctx, uint8_t *dst, uint8_t *src, int width, int height, int dst_linesize, int src_linesize, int r);
};

#endif

从Tlibavcodec定义可以看出，里面包含了大量的ffmpeg中的API，占据了很大的篇幅。通过调用这些API，就可以使用livavcodec的各种功能。

在Tlibavcodec的定义中，有一个变量：Tdll *dll，通过该变量，就可以加载ffmpeg.dll中的方法。

先来看一下Tdll的定义：

/*
*雷霄骅
*leixiaohua1020@126.com
*中国传媒大学/数字电视技术
*/
#ifndef _TDLL_H_
#define _TDLL_H_

#include "Tconfig.h"
//操作Dll的类
class Tdll
{
public:
bool ok;
Tdll(const char_t *dllName1, const Tconfig *config, bool explicitFullPath = false) {
char_t name[MAX_PATH], ext[MAX_PATH];
_splitpath_s(dllName1, NULL, 0, NULL, 0, name, countof(name), ext, countof(ext));
if (config && !explicitFullPath) {
char_t dllName2[MAX_PATH]; //installdir+filename+ext
_makepath_s(dllName2, countof(dllName2), NULL, config->pth, name, ext);
hdll = LoadLibrary(dllName2);
} else {
hdll = NULL;
}
if (!hdll) {
hdll = LoadLibrary(dllName1);
if (!hdll && !explicitFullPath) {
if (config) {
char_t dllName3[MAX_PATH]; //ffdshow.ax_path+filename+ext
_makepath_s(dllName3, countof(dllName3), NULL, config->epth, name, ext);
hdll = LoadLibrary(dllName3);
}
if (!hdll) {
char_t dllName0[MAX_PATH]; //only filename+ext - let Windows find it
_makepath_s(dllName0, countof(dllName0), NULL, NULL, name, ext);
hdll = LoadLibrary(dllName0);
}
}
}
ok = (hdll != NULL);
}
~Tdll() {
if (hdll) {
FreeLibrary(hdll);
}
}
HMODULE hdll;
//封装一下直接加载Dll的GetProcAddress
template<class T> __forceinline void loadFunction(T &fnc, const char *name) {
fnc = hdll ? (T)GetProcAddress(hdll, name) : NULL;
ok &= (fnc != NULL);
}
template<class T> __forceinline void loadFunctionByIndex(T &fnc, uint16_t id) {
uint32_t id32 = uint32_t(id);
fnc = hdll ?
(T) GetProcAddress(hdll, (LPCSTR)id32) :
NULL;
ok &= (fnc != NULL);
}
//检查Dll的状态是否正常
static bool check(const char_t *dllName1, const Tconfig *config) {
char_t name[MAX_PATH], ext[MAX_PATH];
_splitpath_s(dllName1, NULL, 0, NULL, 0, name, countof(name), ext, countof(ext));
if (config) {
char_t dllName2[MAX_PATH]; //installdir+filename+ext
_makepath_s(dllName2, countof(dllName2), NULL, config->pth, name, ext);
if (fileexists(dllName2)) {
return true;
}
}
if (fileexists(dllName1)) {
return true;
}
if (config) {
char_t dllName3[MAX_PATH]; //ffdshow.ax_path+filename+ext
_makepath_s(dllName3, MAX_PATH, NULL, config->epth, name, ext);
if (fileexists(dllName3)) {
return true;
}
}
char_t dllName0[MAX_PATH]; //only filename+ext - let Windows find it
_makepath_s(dllName0, countof(dllName0), NULL, NULL, name, ext);
char_t dir0[MAX_PATH], *dir0flnm;
if (SearchPath(NULL, dllName0, NULL, MAX_PATH, dir0, &dir0flnm)) {
return true;
}
return false;
}
};

#endif

从Tdll的定义可以看出，该类的loadFunction()函数封装了系统使用Dll功能的函数GetProcAddress()。

该类的构造函数Tdll()封装了系统加载Dll的函数LoadLibrary()。

此外该类还提供了check()用于检查Dll。

对于Tdll的分析先告一段落，现在我们回到Tlibavcodec，来看看它是如何加载libavcodec的函数的。查看一下Tlibavcodec的类的实现，位于codecs->libavcodec->Tlibavcodec.cpp。

该类的实现代码比较长，因此只能选择重要的函数查看一下。首先来看一下构造函数：

//===================================== Tlibavcodec ====================================
//FFMPEG封装类的构造函数
Tlibavcodec::Tlibavcodec(const Tconfig *config): refcount(0)
{
//加载FFMPEG的Dll
dll = new Tdll(_l("ffmpeg.dll"), config);
//加载各个函数
dll->loadFunction(avcodec_register_all, "avcodec_register_all");
dll->loadFunction(avcodec_find_decoder, "avcodec_find_decoder");
dll->loadFunction(avcodec_open0, "avcodec_open2");
dll->loadFunction(avcodec_alloc_context0, "avcodec_alloc_context3");
dll->loadFunction(avcodec_alloc_frame, "avcodec_alloc_frame");
dll->loadFunction(avcodec_decode_video2, "avcodec_decode_video2");
dll->loadFunction(avcodec_flush_buffers, "avcodec_flush_buffers");
dll->loadFunction(avcodec_close0, "avcodec_close");
dll->loadFunction(av_log_set_callback, "av_log_set_callback");
dll->loadFunction(av_log_get_callback, "av_log_get_callback");
dll->loadFunction(av_log_get_level, "av_log_get_level");
dll->loadFunction(av_log_set_level, "av_log_set_level");
dll->loadFunction(av_set_cpu_flags_mask, "av_set_cpu_flags_mask");
dll->loadFunction(av_mallocz, "av_mallocz");
dll->loadFunction(av_free, "av_free");
dll->loadFunction(avcodec_default_get_buffer, "avcodec_default_get_buffer");
dll->loadFunction(avcodec_default_release_buffer, "avcodec_default_release_buffer");
dll->loadFunction(avcodec_default_reget_buffer, "avcodec_default_reget_buffer");
dll->loadFunction(avcodec_get_current_idct, "avcodec_get_current_idct");
dll->loadFunction(avcodec_get_encoder_info, "avcodec_get_encoder_info");
dll->loadFunction(av_init_packet, "av_init_packet");
dll->loadFunction(av_packet_new_side_data, "av_packet_new_side_data");
dll->loadFunction(avcodec_h264_search_recovery_point, "avcodec_h264_search_recovery_point");

dll->loadFunction(avcodec_decode_audio3, "avcodec_decode_audio3");

dll->loadFunction(avcodec_find_encoder, "avcodec_find_encoder");
dll->loadFunction(avcodec_encode_video, "avcodec_encode_video");
dll->loadFunction(avcodec_encode_audio, "avcodec_encode_audio");

dll->loadFunction(av_parser_init, "av_parser_init");
dll->loadFunction(av_parser_parse2, "av_parser_parse2");
dll->loadFunction(av_parser_close, "av_parser_close");

//libswscale methods
dll->loadFunction(sws_getCachedContext, "sws_getCachedContext");
dll->loadFunction(sws_freeContext, "sws_freeContext");
dll->loadFunction(sws_getDefaultFilter, "sws_getDefaultFilter");
dll->loadFunction(sws_freeFilter, "sws_freeFilter");
dll->loadFunction(libswscale_sws_scale, "sws_scale");

dll->loadFunction(GetCPUCount, "GetCPUCount");
dll->loadFunction(sws_getConstVec, "sws_getConstVec");
dll->loadFunction(sws_getGaussianVec, "sws_getGaussianVec");
dll->loadFunction(sws_normalizeVec, "sws_normalizeVec");
dll->loadFunction(sws_freeVec, "sws_freeVec");
dll->loadFunction(sws_setColorspaceDetails, "sws_setColorspaceDetails");
dll->loadFunction(sws_getCoefficients, "sws_getCoefficients");

//libpostproc methods
dll->loadFunction(pp_postprocess, "pp_postprocess");
dll->loadFunction(pp_get_context, "pp_get_context");
dll->loadFunction(pp_free_context, "pp_free_context");
dll->loadFunction(ff_simple_idct_mmx, "ff_simple_idct_mmx");

//DXVA methods
dll->loadFunction(av_h264_decode_frame, "av_h264_decode_frame");
dll->loadFunction(av_vc1_decode_frame, "av_vc1_decode_frame");

dll->loadFunction(FFH264CheckCompatibility, "FFH264CheckCompatibility");
dll->loadFunction(FFH264DecodeBuffer, "FFH264DecodeBuffer");
dll->loadFunction(FFH264BuildPicParams, "FFH264BuildPicParams");
dll->loadFunction(FFH264SetCurrentPicture, "FFH264SetCurrentPicture");
dll->loadFunction(FFH264UpdateRefFramesList, "FFH264UpdateRefFramesList");
dll->loadFunction(FFH264IsRefFrameInUse, "FFH264IsRefFrameInUse");
dll->loadFunction(FF264UpdateRefFrameSliceLong, "FF264UpdateRefFrameSliceLong");
dll->loadFunction(FFH264SetDxvaSliceLong, "FFH264SetDxvaSliceLong");

dll->loadFunction(FFVC1UpdatePictureParam, "FFVC1UpdatePictureParam");
dll->loadFunction(FFIsSkipped, "FFIsSkipped");

dll->loadFunction(GetFFMpegPictureType, "GetFFMpegPictureType");
dll->loadFunction(FFGetMBNumber, "FFGetMBNumber");

//yadif methods
dll->loadFunction(yadif_init, "yadif_init");
dll->loadFunction(yadif_uninit, "yadif_uninit");
dll->loadFunction(yadif_filter, "yadif_filter");

//gradfun
dll->loadFunction(gradfunInit, "gradfunInit");
dll->loadFunction(gradfunFilter, "gradfunFilter");

ok = dll->ok;
//加载完毕后，进行注册
if (ok) {
avcodec_register_all();
av_log_set_callback(avlog);
}
}

该构造函数尽管篇幅比较长，但是还是比较好理解的，主要完成了3步：

1. 创建一个Tdll类的对象，加载“ffmpeg.dll”。

2. 使用loadFunction()加载各种函数。

3. 最后调用avcodec_register_all()注册各种解码器。

Tlibavcodec的析构函数则比较简单：

Tlibavcodec::~Tlibavcodec()
{
delete dll;
}

检查Dll的函数也比较简单：

bool Tlibavcodec::check(const Tconfig *config)
{
return Tdll::check(_l("ffmpeg.dll"), config);
}

此外，可能是出于某些功能的考虑，ffdshow还自己写了几个函数，但是限于篇幅不能一一介绍，在这里只介绍一个：
获取libavcodec版本：

bool Tlibavcodec::getVersion(const Tconfig *config, ffstring &vers, ffstring &license)
{
Tdll *dl = new Tdll(_l("ffmpeg.dll"), config);

void (*av_getVersion)(char **version, char **build, char **datetime, const char* *license);
dl->loadFunction(av_getVersion, "getVersion");
bool res;
if (av_getVersion) {
res = true;
char *version, *build, *datetime;
const char *lic;
av_getVersion(&version, &build, &datetime, &lic);
vers = (const char_t*)text<char_t>(version) + ffstring(_l(" (")) + (const char_t*)text<char_t>(datetime) + _l(")");
license = text<char_t>(lic);
} else {
res = false;
vers.clear();
license.clear();
}
delete dl;
return res;
}