XBMC原始碼分析 6：視訊播放器（dvdplayer）-檔案頭（以ffmpeg為例）
阿新 • • 發佈：2019-02-19
XBMC分析系列文章：
XBMC原始碼簡析 5：視訊播放器（dvdplayer）-解複用器（以ffmpeg為例）本文我們分析XBMC中視訊播放器（dvdplayer）中的檔案頭部分。檔案頭部分裡包含的是封裝Dll用到的標頭檔案。由於檔案頭種類很多，不可能一一分析，因此還是以ffmpeg檔案頭為例進行分析。
XBMC中檔案頭部分檔案目錄結構如下圖所示。
在這裡我們看一下封裝AVCodec和AVFormat結構體的標頭檔案，分別是DllAvCodec.h和DllAvFormat.h。
DllAvFormat.h內容如下。其中包含了2個主要的類：DllAvFormatInterface和DllAvFormat。
其中DllAvFormatInterface是一個純虛類，裡面全是純虛擬函式。
DllAvFormat中包含很多已經定義過的巨集，稍後我們分析一下這些巨集的含義。
/* * 雷霄驊 * [email protected] * 中國傳媒大學/數字電視技術 * */ //介面的作用 class DllAvFormatInterface { public: virtual ~DllAvFormatInterface() {} virtual void av_register_all_dont_call(void)=0; virtual void avformat_network_init_dont_call(void)=0; virtual void avformat_network_deinit_dont_call(void)=0; virtual AVInputFormat *av_find_input_format(const char *short_name)=0; virtual void avformat_close_input(AVFormatContext **s)=0; virtual int av_read_frame(AVFormatContext *s, AVPacket *pkt)=0; virtual void av_read_frame_flush(AVFormatContext *s)=0; virtual int av_read_play(AVFormatContext *s)=0; virtual int av_read_pause(AVFormatContext *s)=0; virtual int av_seek_frame(AVFormatContext *s, int stream_index, int64_t timestamp, int flags)=0; #if (!defined USE_EXTERNAL_FFMPEG) && (!defined TARGET_DARWIN) virtual int avformat_find_stream_info_dont_call(AVFormatContext *ic, AVDictionary **options)=0; #endif virtual int avformat_open_input(AVFormatContext **ps, const char *filename, AVInputFormat *fmt, AVDictionary **options)=0; virtual AVIOContext *avio_alloc_context(unsigned char *buffer, int buffer_size, int write_flag, void *opaque, int (*read_packet)(void *opaque, uint8_t *buf, int buf_size), int (*write_packet)(void *opaque, uint8_t *buf, int buf_size), offset_t (*seek)(void *opaque, offset_t offset, int whence))=0; virtual AVInputFormat *av_probe_input_format(AVProbeData *pd, int is_opened)=0; virtual AVInputFormat *av_probe_input_format2(AVProbeData *pd, int is_opened, int *score_max)=0; virtual int av_probe_input_buffer(AVIOContext *pb, AVInputFormat **fmt, const char *filename, void *logctx, unsigned int offset, unsigned int max_probe_size)=0; virtual void av_dump_format(AVFormatContext *ic, int index, const char *url, int is_output)=0; virtual int avio_open(AVIOContext **s, const char *filename, int flags)=0; virtual int avio_close(AVIOContext *s)=0; virtual int avio_open_dyn_buf(AVIOContext **s)=0; virtual int avio_close_dyn_buf(AVIOContext *s, uint8_t **pbuffer)=0; virtual offset_t avio_seek(AVIOContext *s, offset_t offset, int whence)=0; virtual int avio_read(AVIOContext *s, unsigned char *buf, int size)=0; virtual void avio_w8(AVIOContext *s, int b)=0; virtual void avio_write(AVIOContext *s, const unsigned char *buf, int size)=0; virtual void avio_wb24(AVIOContext *s, unsigned int val)=0; virtual void avio_wb32(AVIOContext *s, unsigned int val)=0; virtual void avio_wb16(AVIOContext *s, unsigned int val)=0; virtual AVFormatContext *avformat_alloc_context(void)=0; virtual int avformat_alloc_output_context2(AVFormatContext **ctx, AVOutputFormat *oformat, const char *format_name, const char *filename) = 0; virtual AVStream *avformat_new_stream(AVFormatContext *s, AVCodec *c)=0; virtual AVOutputFormat *av_guess_format(const char *short_name, const char *filename, const char *mime_type)=0; virtual int avformat_write_header (AVFormatContext *s, AVDictionary **options)=0; virtual int av_write_trailer(AVFormatContext *s)=0; virtual int av_write_frame (AVFormatContext *s, AVPacket *pkt)=0; #if defined(AVFORMAT_HAS_STREAM_GET_R_FRAME_RATE) virtual AVRational av_stream_get_r_frame_rate(const AVStream *s)=0; #endif }; //封裝的Dll，繼承了DllDynamic，以及介面 class DllAvFormat : public DllDynamic, DllAvFormatInterface { DECLARE_DLL_WRAPPER(DllAvFormat, DLL_PATH_LIBAVFORMAT) LOAD_SYMBOLS() DEFINE_METHOD0(void, av_register_all_dont_call) DEFINE_METHOD0(void, avformat_network_init_dont_call) DEFINE_METHOD0(void, avformat_network_deinit_dont_call) DEFINE_METHOD1(AVInputFormat*, av_find_input_format, (const char *p1)) DEFINE_METHOD1(void, avformat_close_input, (AVFormatContext **p1)) DEFINE_METHOD1(int, av_read_play, (AVFormatContext *p1)) DEFINE_METHOD1(int, av_read_pause, (AVFormatContext *p1)) DEFINE_METHOD1(void, av_read_frame_flush, (AVFormatContext *p1)) DEFINE_FUNC_ALIGNED2(int, __cdecl, av_read_frame, AVFormatContext *, AVPacket *) DEFINE_FUNC_ALIGNED4(int, __cdecl, av_seek_frame, AVFormatContext*, int, int64_t, int) DEFINE_FUNC_ALIGNED2(int, __cdecl, avformat_find_stream_info_dont_call, AVFormatContext*, AVDictionary **) DEFINE_FUNC_ALIGNED4(int, __cdecl, avformat_open_input, AVFormatContext **, const char *, AVInputFormat *, AVDictionary **) DEFINE_FUNC_ALIGNED2(AVInputFormat*, __cdecl, av_probe_input_format, AVProbeData*, int) DEFINE_FUNC_ALIGNED3(AVInputFormat*, __cdecl, av_probe_input_format2, AVProbeData*, int, int*) DEFINE_FUNC_ALIGNED6(int, __cdecl, av_probe_input_buffer, AVIOContext *, AVInputFormat **, const char *, void *, unsigned int, unsigned int) DEFINE_FUNC_ALIGNED3(int, __cdecl, avio_read, AVIOContext*, unsigned char *, int) DEFINE_FUNC_ALIGNED2(void, __cdecl, avio_w8, AVIOContext*, int) DEFINE_FUNC_ALIGNED3(void, __cdecl, avio_write, AVIOContext*, const unsigned char *, int) DEFINE_FUNC_ALIGNED2(void, __cdecl, avio_wb24, AVIOContext*, unsigned int) DEFINE_FUNC_ALIGNED2(void, __cdecl, avio_wb32, AVIOContext*, unsigned int) DEFINE_FUNC_ALIGNED2(void, __cdecl, avio_wb16, AVIOContext*, unsigned int) DEFINE_METHOD7(AVIOContext *, avio_alloc_context, (unsigned char *p1, int p2, int p3, void *p4, int (*p5)(void *opaque, uint8_t *buf, int buf_size), int (*p6)(void *opaque, uint8_t *buf, int buf_size), offset_t (*p7)(void *opaque, offset_t offset, int whence))) DEFINE_METHOD4(void, av_dump_format, (AVFormatContext *p1, int p2, const char *p3, int p4)) DEFINE_METHOD3(int, avio_open, (AVIOContext **p1, const char *p2, int p3)) DEFINE_METHOD1(int, avio_close, (AVIOContext *p1)) DEFINE_METHOD1(int, avio_open_dyn_buf, (AVIOContext **p1)) DEFINE_METHOD2(int, avio_close_dyn_buf, (AVIOContext *p1, uint8_t **p2)) DEFINE_METHOD3(offset_t, avio_seek, (AVIOContext *p1, offset_t p2, int p3)) DEFINE_METHOD0(AVFormatContext *, avformat_alloc_context) DEFINE_METHOD4(int, avformat_alloc_output_context2, (AVFormatContext **p1, AVOutputFormat *p2, const char *p3, const char *p4)) DEFINE_METHOD2(AVStream *, avformat_new_stream, (AVFormatContext *p1, AVCodec *p2)) DEFINE_METHOD3(AVOutputFormat *, av_guess_format, (const char *p1, const char *p2, const char *p3)) DEFINE_METHOD2(int, avformat_write_header , (AVFormatContext *p1, AVDictionary **p2)) DEFINE_METHOD1(int, av_write_trailer, (AVFormatContext *p1)) DEFINE_METHOD2(int, av_write_frame , (AVFormatContext *p1, AVPacket *p2)) #if defined(AVFORMAT_HAS_STREAM_GET_R_FRAME_RATE) DEFINE_METHOD1(AVRational, av_stream_get_r_frame_rate, (const AVStream *p1)) #endif BEGIN_METHOD_RESOLVE() RESOLVE_METHOD_RENAME(av_register_all, av_register_all_dont_call) RESOLVE_METHOD_RENAME(avformat_network_init, avformat_network_init_dont_call) RESOLVE_METHOD_RENAME(avformat_network_deinit, avformat_network_deinit_dont_call) RESOLVE_METHOD(av_find_input_format) RESOLVE_METHOD(avformat_close_input) RESOLVE_METHOD(av_read_frame) RESOLVE_METHOD(av_read_play) RESOLVE_METHOD(av_read_pause) RESOLVE_METHOD(av_read_frame_flush) RESOLVE_METHOD(av_seek_frame) RESOLVE_METHOD_RENAME(avformat_find_stream_info, avformat_find_stream_info_dont_call) RESOLVE_METHOD(avformat_open_input) RESOLVE_METHOD(avio_alloc_context) RESOLVE_METHOD(av_probe_input_format) RESOLVE_METHOD(av_probe_input_format2) RESOLVE_METHOD(av_probe_input_buffer) RESOLVE_METHOD(av_dump_format) RESOLVE_METHOD(avio_open) RESOLVE_METHOD(avio_close) RESOLVE_METHOD(avio_open_dyn_buf) RESOLVE_METHOD(avio_close_dyn_buf) RESOLVE_METHOD(avio_seek) RESOLVE_METHOD(avio_read) RESOLVE_METHOD(avio_w8) RESOLVE_METHOD(avio_write) RESOLVE_METHOD(avio_wb24) RESOLVE_METHOD(avio_wb32) RESOLVE_METHOD(avio_wb16) RESOLVE_METHOD(avformat_alloc_context) RESOLVE_METHOD(avformat_alloc_output_context2) RESOLVE_METHOD(avformat_new_stream) RESOLVE_METHOD(av_guess_format) RESOLVE_METHOD(avformat_write_header) RESOLVE_METHOD(av_write_trailer) RESOLVE_METHOD(av_write_frame) #if defined(AVFORMAT_HAS_STREAM_GET_R_FRAME_RATE) RESOLVE_METHOD(av_stream_get_r_frame_rate) #endif END_METHOD_RESOLVE() /* dependencies of libavformat */ DllAvCodec m_dllAvCodec; // DllAvUtil loaded implicitely by m_dllAvCodec public: void av_register_all() { CSingleLock lock(DllAvCodec::m_critSection); av_register_all_dont_call(); } int avformat_find_stream_info(AVFormatContext *ic, AVDictionary **options) { CSingleLock lock(DllAvCodec::m_critSection); return avformat_find_stream_info_dont_call(ic, options); } virtual bool Load() { if (!m_dllAvCodec.Load()) return false; bool loaded = DllDynamic::Load(); CSingleLock lock(DllAvCodec::m_critSection); if (++m_avformat_refcnt == 1 && loaded) avformat_network_init_dont_call(); return loaded; } virtual void Unload() { CSingleLock lock(DllAvCodec::m_critSection); if (--m_avformat_refcnt == 0 && DllDynamic::IsLoaded()) avformat_network_deinit_dont_call(); DllDynamic::Unload(); } protected: static int m_avformat_refcnt; }; #endif
這些巨集的含義如下：
DEFINE_METHOD0(result, name) 定義一個方法（不包含引數） DEFINE_METHOD1(result, name, args) 定義一個方法（1個引數） DEFINE_METHOD2(result, name, args) 定義一個方法（2個引數） DEFINE_METHOD3(result, name, args) 定義一個方法（3個引數） DEFINE_METHOD4(result, name, args) 定義一個方法（4個引數） 以此類推... DEFINE_FUNC_ALIGNED0(result, linkage, name) 定義一個方法（不包含引數） DEFINE_FUNC_ALIGNED1(result, linkage, name, t1) 定義一個方法（1個引數） DEFINE_FUNC_ALIGNED2(result, linkage, name, t1, t2) 定義一個方法（2個引數） 以此類推...
可以看一下這些巨集的定義。看了一會，感覺巨集的定義太多了，好亂。在這裡僅舉一個例子：RESOLVE_METHOD
#define RESOLVE_METHOD(method) \
if (!m_dll->ResolveExport( #method , & m_##method##_ptr )) \
return false;DllAvFormat繼承了DllDynamic。DllDynamic是用於載入Dll的類。我們可以看一下它的定義：
//Dll動態載入類
class DllDynamic
{
public:
DllDynamic();
DllDynamic(const CStdString& strDllName);
virtual ~DllDynamic();
virtual bool Load();//載入
virtual void Unload();//解除安裝
virtual bool IsLoaded() const { return m_dll!=NULL; }//是否載入
bool CanLoad();
bool EnableDelayedUnload(bool bOnOff);
bool SetFile(const CStdString& strDllName);//設定檔案
const CStdString &GetFile() const { return m_strDllName; }
protected:
virtual bool ResolveExports()=0;
virtual bool LoadSymbols() { return false; }
bool m_DelayUnload;
LibraryLoader* m_dll;
CStdString m_strDllName;
};
其中有一個變數LibraryLoader* m_dll。是用於載入Dll的。
可以看一DllDynamic中主要的幾個函式，就能明白這個類的作用了。//載入
bool DllDynamic::Load()
{
if (m_dll)
return true;
if (!(m_dll=CSectionLoader::LoadDLL(m_strDllName, m_DelayUnload, LoadSymbols())))
return false;
if (!ResolveExports())
{
CLog::Log(LOGERROR, "Unable to resolve exports from dll %s", m_strDllName.c_str());
Unload();
return false;
}
return true;
}//解除安裝
void DllDynamic::Unload()
{
if(m_dll)
CSectionLoader::UnloadDLL(m_strDllName);
m_dll=NULL;
}//Dll載入類
class LibraryLoader
{
public:
LibraryLoader(const char* libraryFile);
virtual ~LibraryLoader();
virtual bool Load() = 0;
virtual void Unload() = 0;
virtual int ResolveExport(const char* symbol, void** ptr, bool logging = true) = 0;
virtual int ResolveOrdinal(unsigned long ordinal, void** ptr);
virtual bool IsSystemDll() = 0;
virtual HMODULE GetHModule() = 0;
virtual bool HasSymbols() = 0;
char* GetName(); // eg "mplayer.dll"
char* GetFileName(); // "special://xbmcbin/system/mplayer/players/mplayer.dll"
char* GetPath(); // "special://xbmcbin/system/mplayer/players/"
int IncrRef();
int DecrRef();
int GetRef();
private:
LibraryLoader(const LibraryLoader&);
LibraryLoader& operator=(const LibraryLoader&);
char* m_sFileName;
char* m_sPath;
int m_iRefCount;
};
由於自己的作業系統是Windows下的，因此可以看看Win32DllLoader的定義。
//Windows下的Dll載入類
class Win32DllLoader : public LibraryLoader
{
public:
class Import
{
public:
void *table;
DWORD function;
};
Win32DllLoader(const char *dll);
~Win32DllLoader();
virtual bool Load();//載入
virtual void Unload();//解除安裝
virtual int ResolveExport(const char* symbol, void** ptr, bool logging = true);
virtual bool IsSystemDll();
virtual HMODULE GetHModule();
virtual bool HasSymbols();
private:
void OverrideImports(const CStdString &dll);
void RestoreImports();
static bool ResolveImport(const char *dllName, const char *functionName, void **fixup);
static bool ResolveOrdinal(const char *dllName, unsigned long ordinal, void **fixup);
bool NeedsHooking(const char *dllName);
HMODULE m_dllHandle;
bool bIsSystemDll;
std::vector<Import> m_overriddenImports;
std::vector<HMODULE> m_referencedDlls;
};//載入
bool Win32DllLoader::Load()
{
if (m_dllHandle != NULL)
return true;
//檔案路徑
CStdString strFileName = GetFileName();
CStdStringW strDllW;
g_charsetConverter.utf8ToW(CSpecialProtocol::TranslatePath(strFileName), strDllW, false, false, false);
//載入庫
m_dllHandle = LoadLibraryExW(strDllW.c_str(), NULL, LOAD_WITH_ALTERED_SEARCH_PATH);
if (!m_dllHandle)
{
LPVOID lpMsgBuf;
DWORD dw = GetLastError();
FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS, NULL, dw, 0, (LPTSTR) &lpMsgBuf, 0, NULL );
CLog::Log(LOGERROR, "%s: Failed to load %s with error %d:%s", __FUNCTION__, CSpecialProtocol::TranslatePath(strFileName).c_str(), dw, lpMsgBuf);
LocalFree(lpMsgBuf);
return false;
}
// handle functions that the dll imports
if (NeedsHooking(strFileName.c_str()))
OverrideImports(strFileName);
else
bIsSystemDll = true;
return true;
}
//解除安裝
void Win32DllLoader::Unload()
{
// restore our imports
RestoreImports();
//解除安裝庫
if (m_dllHandle)
{
if (!FreeLibrary(m_dllHandle))
CLog::Log(LOGERROR, "%s Unable to unload %s", __FUNCTION__, GetName());
}
m_dllHandle = NULL;
}