av_find_input_format() 

/*** 根据输入格式的短名称查找AVInputFormat。
*/
ff_const59 AVInputFormat *av_find_input_format(const char *short_name);

avformat_open_input() 

/*** 打开一个输入流并读取头。编解码器未打开。 * 必须使用avformat_close_input（）关闭流。** @param ps Pointer to user-supplied AVFormatContext (allocated by avformat_alloc_context).*           May be a pointer to NULL, in which case an AVFormatContext is allocated by this*           function and written into ps.*           Note that a user-supplied AVFormatContext will be freed on failure.* @param url 要打开的流的URL。* @param fmt If non-NULL, this parameter forces a specific input format.*            Otherwise the format is autodetected.* @param options  A dictionary filled with AVFormatContext and demuxer-private options.*                 On return this parameter will be destroyed and replaced with a dict containing*                 options that were not found. May be NULL.** @return 0 on success, a negative AVERROR on failure.** @note If you want to use custom IO, preallocate the format context and set its pb field.*/
int avformat_open_input(AVFormatContext **ps, const char *url, ff_const59 AVInputFormat *fmt, AVDictionary **options);

avformat_close_input() 

/**关闭打开的输入AVFormatContext。释放它和里面的所有东西 并将 *s设置为NULL。*/
void avformat_close_input(AVFormatContext **s);

av_read_frame() 

/*** 返回流的下一帧.* This function returns what is stored in the file, and does not validate* that what is there are valid frames for the decoder. It will split what is* stored in the file into frames and return one for each call. It will not* omit invalid data between valid frames so as to give the decoder the maximum* information possible for decoding.** If pkt->buf is NULL, then the packet is valid until the next* av_read_frame() or until avformat_close_input(). Otherwise the packet* is valid indefinitely. In both cases the packet must be freed with* av_packet_unref when it is no longer needed. For video, the packet contains* exactly one frame. For audio, it contains an integer number of frames if each* frame has a known fixed size (e.g. PCM or ADPCM data). If the audio frames* have a variable size (e.g. MPEG audio), then it contains one frame.** pkt->pts, pkt->dts and pkt->duration are always set to correct* values in AVStream.time_base units (and guessed if the format cannot* provide them). pkt->pts can be AV_NOPTS_VALUE if the video format* has B-frames, so it is better to rely on pkt->dts if you do not* decompress the payload.** @return 0 if OK, < 0 on error or end of file*/
int av_read_frame(AVFormatContext *s, AVPacket *pkt);

av_init_packet() 

/*** 使用默认值初始化数据包的可选字段。.** 注意，这并不涉及data和size成员，它们必须分别初始化。** @param pkt packet*/
void av_init_packet(AVPacket *pkt);

av_packet_unref（） 

/*** 把包擦干净。** 取消引用数据包所引用的缓冲区，并重置* 其余分组字段设置为它们的默认值。** @param pkt The packet to be unreferenced.*/
void av_packet_unref(AVPacket *pkt);

av_packet_alloc() 

/* 分配AVPacket并将其字段设置为默认值。  结果* 必须使用av_packet_free（）释放结构。** @return一个AVPacket，在失败时填充默认值或NULL。** @注意，这仅分配AVPacket本身，而不是数据缓冲区。那些* 必须通过诸如av_new_packet的其它手段来分配。*/
AVPacket *av_packet_alloc(void);

av_packet_free() 

/**释放数据包，如果数据包被引用计数，它将* 未引用第一。** @param要释放的pkt包。指针将被设置为NULL。* @note传递NULL是一个空操作。*/
void av_packet_free(AVPacket **pkt);