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FFMPEG结构体分析#xff1a;AVIOContext_雷霄骅的博客-CSDN博客_aviocontext
AVIOContext
AVIOContext是FFMPEG管理输入输出数据的结构体结构体的定义位于位于avio.h关键的变量如下所示
unsigned char *buffer#xff1a;缓存开始位置int buffer_size#xff1…参考链接
FFMPEG结构体分析AVIOContext_雷霄骅的博客-CSDN博客_aviocontext
AVIOContext
AVIOContext是FFMPEG管理输入输出数据的结构体结构体的定义位于位于avio.h关键的变量如下所示
unsigned char *buffer缓存开始位置int buffer_size缓存大小默认32768unsigned char *buf_ptr当前指针读取到的位置unsigned char *buf_end缓存结束的位置void *opaqueURLContext结构体 在解码的情况下buffer用于存储ffmpeg读入的数据。例如打开一个视频文件的时候先把数据从硬盘读入buffer然后在送给解码器用于解码。/*** A callback that is used instead of write_packet.*/int (*write_data_type)(void *opaque, uint8_t *buf, int buf_size,enum AVIODataMarkerType type, int64_t time);
其中opaque指向了URLContext。不是很理解这句话的含义涉及到write_data_type的一共仅有三处 第一部分函数的定义第二部分if判断第三部分函数的调用 注意这个结构体并不在FFMPEG提供的头文件中而是在FFMPEG的源代码中。修正目前在url.h文件中URLContext结构体中还有一个结构体URLProtocol注每种协议rtprtmpfile等对应一个URLProtocol
typedef struct URLProtocol {const char *name;int (*url_open)( URLContext *h, const char *url, int flags);/*** This callback is to be used by protocols which open further nested* protocols. options are then to be passed to ffurl_open_whitelist()* or ffurl_connect() for those nested protocols.*/int (*url_open2)(URLContext *h, const char *url, int flags, AVDictionary **options);int (*url_accept)(URLContext *s, URLContext **c);int (*url_handshake)(URLContext *c);/*** Read data from the protocol.* If data is immediately available (even less than size), EOF is* reached or an error occurs (including EINTR), return immediately.* Otherwise:* In non-blocking mode, return AVERROR(EAGAIN) immediately.* In blocking mode, wait for data/EOF/error with a short timeout (0.1s),* and return AVERROR(EAGAIN) on timeout.* Checking interrupt_callback, looping on EINTR and EAGAIN and until* enough data has been read is left to the calling function; see* retry_transfer_wrapper in avio.c.*/int (*url_read)( URLContext *h, unsigned char *buf, int size);int (*url_write)(URLContext *h, const unsigned char *buf, int size);int64_t (*url_seek)( URLContext *h, int64_t pos, int whence);int (*url_close)(URLContext *h);int (*url_read_pause)(URLContext *h, int pause);int64_t (*url_read_seek)(URLContext *h, int stream_index,int64_t timestamp, int flags);int (*url_get_file_handle)(URLContext *h);int (*url_get_multi_file_handle)(URLContext *h, int **handles,int *numhandles);int (*url_get_short_seek)(URLContext *h);int (*url_shutdown)(URLContext *h, int flags);const AVClass *priv_data_class;int priv_data_size;int flags;int (*url_check)(URLContext *h, int mask);int (*url_open_dir)(URLContext *h);int (*url_read_dir)(URLContext *h, AVIODirEntry **next);int (*url_close_dir)(URLContext *h);int (*url_delete)(URLContext *h);int (*url_move)(URLContext *h_src, URLContext *h_dst);const char *default_whitelist;
} URLProtocol;在这个结构体中除了一些回调函数接口之外有一个变量const char *name该变量存储了协议的名称。每一种输入协议都对应这样一个结构体。
文件协议 数据结构ff_file_protocol
位于file.c函数指针 指向具体的执行函数等号右边的函数是完成具体读写功能的函数。可以看一下file协议的几个函数其实就是读文件写文件这样的操作
const URLProtocol ff_file_protocol {.name file,.url_open file_open,.url_read file_read,.url_write file_write,.url_seek file_seek,.url_close file_close,.url_get_file_handle file_get_handle,.url_check file_check,.url_delete file_delete,.url_move file_move,.priv_data_size sizeof(FileContext),.priv_data_class file_class,.url_open_dir file_open_dir,.url_read_dir file_read_dir,.url_close_dir file_close_dir,.default_whitelist file,crypto,data
};
static int file_read(URLContext *h, unsigned char *buf, int size)
{FileContext *c h-priv_data;int ret;size FFMIN(size, c-blocksize);ret read(c-fd, buf, size);if (ret 0 c-follow)return AVERROR(EAGAIN);if (ret 0)return AVERROR_EOF;return (ret -1) ? AVERROR(errno) : ret;
}static int file_write(URLContext *h, const unsigned char *buf, int size)
{FileContext *c h-priv_data;int ret;size FFMIN(size, c-blocksize);ret write(c-fd, buf, size);return (ret -1) ? AVERROR(errno) : ret;
}static int file_get_handle(URLContext *h)
{FileContext *c h-priv_data;return c-fd;
}static int file_check(URLContext *h, int mask)
{int ret 0;const char *filename h-filename;av_strstart(filename, file:, filename);{
#if HAVE_ACCESS defined(R_OK)if (access(filename, F_OK) 0)return AVERROR(errno);if (maskAVIO_FLAG_READ)if (access(filename, R_OK) 0)ret | AVIO_FLAG_READ;if (maskAVIO_FLAG_WRITE)if (access(filename, W_OK) 0)ret | AVIO_FLAG_WRITE;
#elsestruct stat st;ret stat(filename, st);if (ret 0)return AVERROR(errno);ret | st.st_modeS_IRUSR ? maskAVIO_FLAG_READ : 0;ret | st.st_modeS_IWUSR ? maskAVIO_FLAG_WRITE : 0;
#endif}return ret;
}#if CONFIG_FILE_PROTOCOLstatic int file_delete(URLContext *h)
{
#if HAVE_UNISTD_Hint ret;const char *filename h-filename;av_strstart(filename, file:, filename);ret rmdir(filename);if (ret 0 (errno ENOTDIR
# ifdef _WIN32|| errno EINVAL
# endif))ret unlink(filename);if (ret 0)return AVERROR(errno);return ret;
#elsereturn AVERROR(ENOSYS);
#endif /* HAVE_UNISTD_H */
}static int file_move(URLContext *h_src, URLContext *h_dst)
{const char *filename_src h_src-filename;const char *filename_dst h_dst-filename;av_strstart(filename_src, file:, filename_src);av_strstart(filename_dst, file:, filename_dst);if (rename(filename_src, filename_dst) 0)return AVERROR(errno);return 0;
}static int file_open(URLContext *h, const char *filename, int flags)
{FileContext *c h-priv_data;int access;int fd;struct stat st;av_strstart(filename, file:, filename);if (flags AVIO_FLAG_WRITE flags AVIO_FLAG_READ) {access O_CREAT | O_RDWR;if (c-trunc)access | O_TRUNC;} else if (flags AVIO_FLAG_WRITE) {access O_CREAT | O_WRONLY;if (c-trunc)access | O_TRUNC;} else {access O_RDONLY;}
#ifdef O_BINARYaccess | O_BINARY;
#endiffd avpriv_open(filename, access, 0666);if (fd -1)return AVERROR(errno);c-fd fd;h-is_streamed !fstat(fd, st) S_ISFIFO(st.st_mode);/* Buffer writes more than the default 32k to improve throughput especially* with networked file systems */if (!h-is_streamed flags AVIO_FLAG_WRITE)h-min_packet_size h-max_packet_size 262144;if (c-seekable 0)h-is_streamed !c-seekable;return 0;
}/* XXX: use llseek */
static int64_t file_seek(URLContext *h, int64_t pos, int whence)
{FileContext *c h-priv_data;int64_t ret;if (whence AVSEEK_SIZE) {struct stat st;ret fstat(c-fd, st);return ret 0 ? AVERROR(errno) : (S_ISFIFO(st.st_mode) ? 0 : st.st_size);}ret lseek(c-fd, pos, whence);return ret 0 ? AVERROR(errno) : ret;
}static int file_close(URLContext *h)
{FileContext *c h-priv_data;int ret close(c-fd);return (ret -1) ? AVERROR(errno) : 0;
}static int file_open_dir(URLContext *h)
{
#if HAVE_LSTATFileContext *c h-priv_data;c-dir opendir(h-filename);if (!c-dir)return AVERROR(errno);return 0;
#elsereturn AVERROR(ENOSYS);
#endif /* HAVE_LSTAT */
}static int file_read_dir(URLContext *h, AVIODirEntry **next)
{
#if HAVE_LSTATFileContext *c h-priv_data;struct dirent *dir;char *fullpath NULL;*next ff_alloc_dir_entry();if (!*next)return AVERROR(ENOMEM);do {errno 0;dir readdir(c-dir);if (!dir) {av_freep(next);return AVERROR(errno);}} while (!strcmp(dir-d_name, .) || !strcmp(dir-d_name, ..));fullpath av_append_path_component(h-filename, dir-d_name);if (fullpath) {struct stat st;if (!lstat(fullpath, st)) {if (S_ISDIR(st.st_mode))(*next)-type AVIO_ENTRY_DIRECTORY;else if (S_ISFIFO(st.st_mode))(*next)-type AVIO_ENTRY_NAMED_PIPE;else if (S_ISCHR(st.st_mode))(*next)-type AVIO_ENTRY_CHARACTER_DEVICE;else if (S_ISBLK(st.st_mode))(*next)-type AVIO_ENTRY_BLOCK_DEVICE;else if (S_ISLNK(st.st_mode))(*next)-type AVIO_ENTRY_SYMBOLIC_LINK;else if (S_ISSOCK(st.st_mode))(*next)-type AVIO_ENTRY_SOCKET;else if (S_ISREG(st.st_mode))(*next)-type AVIO_ENTRY_FILE;else(*next)-type AVIO_ENTRY_UNKNOWN;(*next)-group_id st.st_gid;(*next)-user_id st.st_uid;(*next)-size st.st_size;(*next)-filemode st.st_mode 0777;(*next)-modification_timestamp INT64_C(1000000) * st.st_mtime;(*next)-access_timestamp INT64_C(1000000) * st.st_atime;(*next)-status_change_timestamp INT64_C(1000000) * st.st_ctime;}av_free(fullpath);}(*next)-name av_strdup(dir-d_name);return 0;
#elsereturn AVERROR(ENOSYS);
#endif /* HAVE_LSTAT */
}static int file_close_dir(URLContext *h)
{
#if HAVE_LSTATFileContext *c h-priv_data;closedir(c-dir);return 0;
#elsereturn AVERROR(ENOSYS);
#endif /* HAVE_LSTAT */
} libRTMP
位于librtmp.c
RTMP_CLASS(rtmp)
const URLProtocol ff_librtmp_protocol {.name rtmp,.url_open rtmp_open,.url_read rtmp_read,.url_write rtmp_write,.url_close rtmp_close,.url_read_pause rtmp_read_pause,.url_read_seek rtmp_read_seek,.url_get_file_handle rtmp_get_file_handle,.priv_data_size sizeof(LibRTMPContext),.priv_data_class librtmp_class,.flags URL_PROTOCOL_FLAG_NETWORK,
};RTMP_CLASS(rtmpt)
const URLProtocol ff_librtmpt_protocol {.name rtmpt,.url_open rtmp_open,.url_read rtmp_read,.url_write rtmp_write,.url_close rtmp_close,.url_read_pause rtmp_read_pause,.url_read_seek rtmp_read_seek,.url_get_file_handle rtmp_get_file_handle,.priv_data_size sizeof(LibRTMPContext),.priv_data_class librtmpt_class,.flags URL_PROTOCOL_FLAG_NETWORK,
};RTMP_CLASS(rtmpe)
const URLProtocol ff_librtmpe_protocol {.name rtmpe,.url_open rtmp_open,.url_read rtmp_read,.url_write rtmp_write,.url_close rtmp_close,.url_read_pause rtmp_read_pause,.url_read_seek rtmp_read_seek,.url_get_file_handle rtmp_get_file_handle,.priv_data_size sizeof(LibRTMPContext),.priv_data_class librtmpe_class,.flags URL_PROTOCOL_FLAG_NETWORK,
};RTMP_CLASS(rtmpte)
const URLProtocol ff_librtmpte_protocol {.name rtmpte,.url_open rtmp_open,.url_read rtmp_read,.url_write rtmp_write,.url_close rtmp_close,.url_read_pause rtmp_read_pause,.url_read_seek rtmp_read_seek,.url_get_file_handle rtmp_get_file_handle,.priv_data_size sizeof(LibRTMPContext),.priv_data_class librtmpte_class,.flags URL_PROTOCOL_FLAG_NETWORK,
};RTMP_CLASS(rtmps)
const URLProtocol ff_librtmps_protocol {.name rtmps,.url_open rtmp_open,.url_read rtmp_read,.url_write rtmp_write,.url_close rtmp_close,.url_read_pause rtmp_read_pause,.url_read_seek rtmp_read_seek,.url_get_file_handle rtmp_get_file_handle,.priv_data_size sizeof(LibRTMPContext),.priv_data_class librtmps_class,.flags URL_PROTOCOL_FLAG_NETWORK,
}; udp协议
位于udp.c
const URLProtocol ff_udp_protocol {.name udp,.url_open udp_open,.url_read udp_read,.url_write udp_write,.url_close udp_close,.url_get_file_handle udp_get_file_handle,.priv_data_size sizeof(UDPContext),.priv_data_class udp_class,.flags URL_PROTOCOL_FLAG_NETWORK,
};const URLProtocol ff_udplite_protocol {.name udplite,.url_open udplite_open,.url_read udp_read,.url_write udp_write,.url_close udp_close,.url_get_file_handle udp_get_file_handle,.priv_data_size sizeof(UDPContext),.priv_data_class udplite_context_class,.flags URL_PROTOCOL_FLAG_NETWORK,
};代码
/*** Bytestream IO Context. //字节流 IO 上下文* New public fields can be added with minor version bumps. //新的公共字段可以添加小版本颠簸* Removal, reordering and changes to existing public fields require * a major version bump. 移除、重新排序和更改现有公共字段需要一个主要版本的凹凸* sizeof(AVIOContext) must not be used outside libav*. //sizeof(AVIOContext) 不得在 libav* 之外使用** note None of the function pointers in AVIOContext should be called* directly, they should only be set by the client application* when implementing custom I/O. Normally these are set to the* function pointers specified in avio_alloc_context()* AVIOContext 中的任何函数指针都不应直接调用它们只能由客户端应用程序* 在实现自定义 I/O 时设置。 通常这些设置为 avio_alloc_context() 中指定的函数指针*/
typedef struct AVIOContext {/*** A class for private options. //一个私人选项类** If this AVIOContext is created by avio_open2(), av_class is set and* passes the options down to protocols.* 如果此 AVIOContext 由 avio_open2() 创建则设置 av_class 并将选项传递给协议** If this AVIOContext is manually allocated, then av_class may be set by* the caller.* 如果这个 AVIOContext 是手动分配的那么 av_class 可能由调用者设置* * warning -- this field can be NULL, be sure to not pass this AVIOContext * to any av_opt_* functions in that case.* 警告——该字段可以为 NULL在这种情况下请确保不要将此 AVIOContext 传递给任何 av_opt_* 函数*/const AVClass *av_class;/** The following shows the relationship between buffer, buf_ptr,* buf_ptr_max, buf_end, buf_size, and pos, when reading and when writing* (since AVIOContext is used for both):************************************************************************************ READING************************************************************************************ | buffer_size |* |---------------------------------------|* | |** buffer buf_ptr buf_end* --------------------------------------* |/ / / / / / / /|/ / / / / / /| |* read buffer: |/ / consumed / | to be read /| |* |/ / / / / / / /|/ / / / / / /| |* --------------------------------------** pos* ------------------------------------------------------------* input file: | | |* ------------------------------------------------------------************************************************************************************* WRITING************************************************************************************ | buffer_size |* |--------------------------------------|* | |** buf_ptr_max* buffer (buf_ptr) buf_end* -------------------------------------* |/ / / / / / / / / / / /| |* write buffer: | / / to be flushed / / | |* |/ / / / / / / / / / / /| |* -------------------------------------* buf_ptr can be in this* due to a backward seek** pos* -----------------------------------------------------------* output file: | | |* -----------------------------------------------------------**/unsigned char *buffer; /** Start of the buffer. */int buffer_size; /** Maximum buffer size */unsigned char *buf_ptr; /** Current position in the buffer */unsigned char *buf_end; /** End of the data, may be less thanbufferbuffer_size if the read function returnedless data than requested, e.g. for streams whereno more data has been received yet. */void *opaque; /** A private pointer, passed to the read/write/seek/...functions. */int (*read_packet)(void *opaque, uint8_t *buf, int buf_size);int (*write_packet)(void *opaque, uint8_t *buf, int buf_size);int64_t (*seek)(void *opaque, int64_t offset, int whence);int64_t pos; /** position in the file of the current buffer */int eof_reached; /** true if was unable to read due to error or eof */int error; /** contains the error code or 0 if no error happened */int write_flag; /** true if open for writing */int max_packet_size;int min_packet_size; /** Try to buffer at least this amount of databefore flushing it. */unsigned long checksum;unsigned char *checksum_ptr;unsigned long (*update_checksum)(unsigned long checksum, const uint8_t *buf, unsigned int size);/*** Pause or resume playback for network streaming protocols - e.g. MMS.*/int (*read_pause)(void *opaque, int pause);/*** Seek to a given timestamp in stream with the specified stream_index.* Needed for some network streaming protocols which dont support seeking* to byte position.*/int64_t (*read_seek)(void *opaque, int stream_index,int64_t timestamp, int flags);/*** A combination of AVIO_SEEKABLE_ flags or 0 when the stream is not seekable.*/int seekable;/*** avio_read and avio_write should if possible be satisfied directly* instead of going through a buffer, and avio_seek will always* call the underlying seek function directly.*/int direct;/*** , separated list of allowed protocols.*/const char *protocol_whitelist;/*** , separated list of disallowed protocols.*/const char *protocol_blacklist;/*** A callback that is used instead of write_packet.*/int (*write_data_type)(void *opaque, uint8_t *buf, int buf_size,enum AVIODataMarkerType type, int64_t time);/*** If set, dont call write_data_type separately for AVIO_DATA_MARKER_BOUNDARY_POINT,* but ignore them and treat them as AVIO_DATA_MARKER_UNKNOWN (to avoid needlessly* small chunks of data returned from the callback).*/int ignore_boundary_point;#if FF_API_AVIOCONTEXT_WRITTEN/*** deprecated field utilized privately by libavformat. For a public* statistic of how many bytes were written out, see* AVIOContext::bytes_written.*/attribute_deprecatedint64_t written;
#endif/*** Maximum reached position before a backward seek in the write buffer,* used keeping track of already written data for a later flush.*/unsigned char *buf_ptr_max;/*** Read-only statistic of bytes read for this AVIOContext.*/int64_t bytes_read;/*** Read-only statistic of bytes written for this AVIOContext.*/int64_t bytes_written;
} AVIOContext;
