南京做网站的,页面设计师自我介绍,成品源码1277,电子商务网站建设与运维论文【FFmpeg】AVIOContext结构体 1.AVIOContext结构体的定义 参考#xff1a; FFMPEG结构体分析#xff1a;AVIOContext
示例工程#xff1a; 【FFmpeg】调用ffmpeg库实现264软编 【FFmpeg】调用ffmpeg库实现264软解 【FFmpeg】调用ffmpeg库进行RTMP推流和拉流 【FFmpeg】调用… 【FFmpeg】AVIOContext结构体 1.AVIOContext结构体的定义 参考 FFMPEG结构体分析AVIOContext
示例工程 【FFmpeg】调用ffmpeg库实现264软编 【FFmpeg】调用ffmpeg库实现264软解 【FFmpeg】调用ffmpeg库进行RTMP推流和拉流 【FFmpeg】调用ffmpeg库进行SDL2解码后渲染
流程分析 【FFmpeg】编码链路上主要函数的简单分析 【FFmpeg】解码链路上主要函数的简单分析
结构体分析 【FFmpeg】AVCodec结构体 【FFmpeg】AVCodecContext结构体 【FFmpeg】AVStream结构体 【FFmpeg】AVFormatContext结构体
1.AVIOContext结构体的定义
AVIOContext定义了输入输出上下文之中的信息涉及到码流的输入输出是非常重要的结构体位于libavformat\avio.h中定义如下
/*** Bytestream IO Context.* New public fields can be added with minor version bumps.* Removal, reordering and changes to existing public fields require* a major version bump.* sizeof(AVIOContext) must not be used outside libav*.** 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()*/
// 码流输入输出的上下文
// note AVIOContext中的所有函数指针都不应该被直接调用它们只应该由客户端应用程序在实现自定义I/O时设置
// 通常将这些设置为avio_alloc_context()中指定的函数指针
typedef struct AVIOContext {/*** A class for private options.** If this AVIOContext is created by avio_open2(), av_class is set and* passes the options down to protocols.** If this AVIOContext is manually allocated, then av_class may be set by* the caller.** warning -- this field can be NULL, be sure to not pass this AVIOContext* to any av_opt_* functions in that case.*/// 用于私有配置的选项// 如果这个AVIOContext是由avio_open2创建的设置av_class并将选项向下传递给协议// 如果这个AVIOContext是手动分配的那么av_class可以由调用者设置// warning: 这个字段可以为NULL在这种情况下请确保不要将这个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: | | |* -----------------------------------------------------------**/// buffer的起始地址unsigned char *buffer; /** Start of the buffer. */// 最大的buffer大小int buffer_size; /** Maximum buffer size */// 当前buffer指针指向的位置unsigned char *buf_ptr; /** Current position in the buffer */// 如果read函数返回的数据少于请求则数据的结束值可能小于bufferbuffer_size例如对于尚未接收到更多数据的流// 当前buffer指针的末尾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. */// 私有指针传递给read/write/seek/… 函数void *opaque; /** A private pointer, passed to the read/write/seek/...functions. */// 读取packetint (*read_packet)(void *opaque, uint8_t *buf, int buf_size);// 写入packetint (*write_packet)(void *opaque, const uint8_t *buf, int buf_size);// 查找int64_t (*seek)(void *opaque, int64_t offset, int whence);// 当前缓冲区在文件中的位置int64_t pos; /** position in the file of the current buffer */// 如果由于错误或eof而无法读取则为Trueint eof_reached; /** true if was unable to read due to error or eof */// 错误码int error; /** contains the error code or 0 if no error happened */// 如果是写入状态则置为trueint write_flag; /** true if open for writing */// 最大的packet大小int max_packet_size;// 最小的packet大小(在刷新数据之前尝试至少缓冲这么多的数据)int min_packet_size; /** Try to buffer at least this amount of databefore flushing it. */// checksum用于验证数据完整性// 存储了校验值以验证数据的完整性。通过将数据块的大小累加到checksum然后对结果进行按位反转来实现的// 这个机制主要用于检测数据传输过程中可能发生的错误尤其是在网络传输或文件读写中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.*/// 暂停或恢复网络流协议的播放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.*/// 使用指定的stream_index在流中查找给定的时间戳// 需要一些网络流协议不支持寻求字节位置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.*//*流查找的行为有两个定义* Seeking works like for a local file.#define AVIO_SEEKABLE_NORMAL (1 0)* Seeking by timestamp with avio_seek_time() is possible.#define AVIO_SEEKABLE_TIME (1 1)*/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.*/// 如果可能的话应该直接满足Avio_read和avio_write而不是通过缓冲区avio_seek将始终直接调用底层的seek函数int direct;/*** , separated list of allowed protocols.*/// 协议的白名单const char *protocol_whitelist;/*** , separated list of disallowed protocols.*/// 协议的黑名单const char *protocol_blacklist;/*** A callback that is used instead of write_packet.*/// 一个用来代替write_packet的回调int (*write_data_type)(void *opaque, const 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).*/// 如果设置了不要为AVIO_DATA_MARKER_BOUNDARY_POINT单独调用write_data_type// 而是忽略它们并将它们视为AVIO_DATA_MARKER_UNKNOWN(以避免从回调返回不必要的小块数据)int ignore_boundary_point;/*** Maximum reached position before a backward seek in the write buffer,* used keeping track of already written data for a later flush.*/// 写缓冲区中向后寻道之前达到的最大位置用于跟踪已写入的数据以便以后刷新unsigned char *buf_ptr_max;/*** Read-only statistic of bytes read for this AVIOContext.*/// 只读统计为该AVIOContext读取的字节数int64_t bytes_read;/*** Read-only statistic of bytes written for this AVIOContext.*/// 只读统计写入该AVIOContext的字节数。int64_t bytes_written;
} AVIOContext;AVIOContext当中比较重要的信息包括 1unsigned char *bufferbuffer的起始地址 2int buffer_sizebuffer的大小 3unsigned char *buf_ptrbuffer当前的指针 4unsigned char *buf_endbuffer末尾的地址 5void *opaqueURLContext 6int (*read_packet)(void *opaque, uint8_t *buf, int buf_size)读取packet 7int (*write_packet)(void *opaque, const uint8_t *buf, int buf_size)写入packet 8int64_t (*seek)(void *opaque, int64_t offset, int whence)定位查找 9unsigned long (*update_checksum)(unsigned long checksum, const uint8_t *buf, unsigned int size)更新校验信息checksum 10int (*read_pause)(void *opaque, int pause)暂停流的读取 11const char *protocol_XXXlist协议的黑白名单
相对比于雷博记录的内容新版本的AVIOContext增加的比较重要的是协议的黑白名单白名单当中的protocol表示可用黑名单当中的protocol表示不可用。在解码的时候buffer会存储FFmpeg读取的数据例如解码已经编码好的.h264文件。
URLContext的定义如下位于libavformat\url.h中
typedef struct URLContext {const AVClass *av_class; /** information for av_log(). Set by url_open(). */const struct URLProtocol *prot;void *priv_data;char *filename; /** specified URL */int flags;int max_packet_size; /** if non zero, the stream is packetized with this max packet size */int is_streamed; /** true if streamed (no seek possible), default false */int is_connected;AVIOInterruptCB interrupt_callback;int64_t rw_timeout; /** maximum time to wait for (network) read/write operation completion, in mcs */const char *protocol_whitelist;const char *protocol_blacklist;int min_packet_size; /** if non zero, the stream is packetized with this min packet size */
} URLContext;相对于老版本的FFmpeg这里一个比较大的改变是增加了protocol的黑白名单。URLProtocol的定义如下同样位于libavformat\url.h中
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.*/// 此回调将由打开进一步嵌套协议的协议使用。然后将这些嵌套协议的选项传递给ffurl_open_whitelist()或ffurl_connect()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.*/// 从protocol读取数据// 如果数据立即可用(甚至小于大小)达到EOF或发生错误(包括EINTR)则立即返回// 在非阻塞模式下立即返回AVERROR(EAGAIN)。在阻塞模式下等待数据/EOF/错误有一个短超时(0.1s)并在超时时返回AVERROR(EAGAIN)// 检查interrupt_callback在EINTR和EAGAIN上循环直到有足够的数据被读取给调用函数;参见avio.c中的retry_transfer_wrapperint (*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)(void *urlcontext, int pause);int64_t (*url_read_seek)(void *urlcontext, 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;// 相对比于老版本的FFmpeg这里还增加了dir的操作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;在实际的结构体定义如下所示定义是file的protocol其中还定义了白名单为file,crypto,data
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
};又比如tcp的protocol不过这里没有定义默认的白名单
const URLProtocol ff_tcp_protocol {.name tcp,.url_open tcp_open,.url_accept tcp_accept,.url_read tcp_read,.url_write tcp_write,.url_close tcp_close,.url_get_file_handle tcp_get_file_handle,.url_get_short_seek tcp_get_window_size,.url_shutdown tcp_shutdown,.priv_data_size sizeof(TCPContext),.flags URL_PROTOCOL_FLAG_NETWORK,.priv_data_class tcp_class,
};CSDN : https://blog.csdn.net/weixin_42877471 Github : https://github.com/DoFulangChen
