该结构体的定义在avformat.h文件中：
typedef struct AVOutputFormat { const char *name; /** * Descriptive name for the format, meant to be more human-readable * than name. You should use the NULL_IF_CONFIG_SMALL() macro * to define it. */ const char *long_name; const char *mime_type; const char *extensions; /**< comma-separated filename extensions */ /* output support */ enum AVCodecID audio_codec; /**< default audio codec */ enum AVCodecID video_codec; /**< default video codec */ enum AVCodecID subtitle_codec; /**< default subtitle codec */ /** * can use flags: AVFMT_NOFILE, AVFMT_NEEDNUMBER, AVFMT_RAWPICTURE, * AVFMT_GLOBALHEADER, AVFMT_NOTIMESTAMPS, AVFMT_VARIABLE_FPS, * AVFMT_NODIMENSIONS, AVFMT_NOSTREAMS, AVFMT_ALLOW_FLUSH, * AVFMT_TS_NONSTRICT */ int flags; /** * List of supported codec_id-codec_tag pairs, ordered by "better * choice first". The arrays are all terminated by AV_CODEC_ID_NONE. */ const struct AVCodecTag * const *codec_tag; const AVClass *priv_class; ///< AVClass for the private context /***************************************************************** * No fields below this line are part of the public API. They * may not be used outside of libavformat and can be changed and * removed at will. * New public fields should be added right above. ***************************************************************** */ struct AVOutputFormat *next; /** * size of private data so that it can be allocated in the wrapper */ int priv_data_size; int (*write_header)(struct AVFormatContext *); /** * Write a packet. If AVFMT_ALLOW_FLUSH is set in flags, * pkt can be NULL in order to flush data buffered in the muxer. * When flushing, return 0 if there still is more data to flush, * or 1 if everything was flushed and there is no more buffered * data. */ int (*write_packet)(struct AVFormatContext *, AVPacket *pkt); int (*write_trailer)(struct AVFormatContext *); /** * Currently only used to set pixel format if not YUV420P. */ int (*interleave_packet)(struct AVFormatContext *, AVPacket *out, AVPacket *in, int flush); /** * Test if the given codec can be stored in this container. * * @return 1 if the codec is supported, 0 if it is not. * A negative number if unknown. * MKTAG('A', 'P', 'I', 'C') if the codec is only supported as AV_DISPOSITION_ATTACHED_PIC */ int (*query_codec)(enum AVCodecID id, int std_compliance); void (*get_output_timestamp)(struct AVFormatContext *s, int stream, int64_t *dts, int64_t *wall); /** * Allows sending messages from application to device. */ int (*control_message)(struct AVFormatContext *s, int type, void *data, size_t data_size); /** * Write an uncoded AVFrame. * * See av_write_uncoded_frame() for details. * * The library will free *frame afterwards, but the muxer can prevent it * by setting the pointer to NULL. */ int (*write_uncoded_frame)(struct AVFormatContext *, int stream_index, AVFrame **frame, unsigned flags); /** * Returns device list with it properties. * @see avdevice_list_devices() for more details. */ int (*get_device_list)(struct AVFormatContext *s, struct AVDeviceInfoList *device_list); /** * Initialize device capabilities submodule. * @see avdevice_capabilities_create() for more details. */ int (*create_device_capabilities)(struct AVFormatContext *s, struct AVDeviceCapabilitiesQuery *caps); /** * Free device capabilities submodule. * @see avdevice_capabilities_free() for more details. */ int (*free_device_capabilities)(struct AVFormatContext *s, struct AVDeviceCapabilitiesQuery *caps); enum AVCodecID data_codec; /**< default data codec */ } AVOutputFormat;
官方参考地址：http://ffmpeg.org/doxygen/3.1/structAVOutputFormat.html
在文件avformat.h中，第1350行中，结构体AVFormatContext中有：struct AVOutputFormat *oformat，注释中写：
The output container format. Muxing only, must be set by the caller before avformat_write_header().
AVFormatContext的初始化可以用:
AVOutputFormat *av_guess_format(const char *short_name, const char *filename, const char *mime_type);
参考：http://blog.csdn.net/yibu_refresh/article/details/52881717