1.描述
AVOutpufFormat与AVInputFormat类似，是类似COM 接口的数据结构，表示输出文件容器格式，着重于功能函数，位于Avoformat.h文件中。
ffmpeg支持各种各样的输出文件格式，MP4，FLV，3GP等等。而 AVOutputFormat 结构体则保存了这些格式的信息和一些常规设置。
每一种封装对应一个 AVOutputFormat 结构，ffmpeg将AVOutputFormat 按照链表存储：
2.结构体定义
1 typedef struct AVOutputFormat {
2 const char *name;
3 /**
4 * Descriptive name for the format, meant to be more human-readable
5 * than name. You should use the NULL_IF_CONFIG_SMALL() macro
6 * to define it.
7 */
8 const char *long_name;
9 const char *mime_type;
10 const char *extensions; /**< comma-separated filename extensions */
11 /* output support */
12 enum AVCodecID audio_codec; /**< default audio codec */
13 enum AVCodecID video_codec; /**< default video codec */
14 enum AVCodecID subtitle_codec; /**< default subtitle codec */
15 /**
16 * can use flags: AVFMT_NOFILE, AVFMT_NEEDNUMBER,
17 * AVFMT_GLOBALHEADER, AVFMT_NOTIMESTAMPS, AVFMT_VARIABLE_FPS,
18 * AVFMT_NODIMENSIONS, AVFMT_NOSTREAMS, AVFMT_ALLOW_FLUSH,
19 * AVFMT_TS_NONSTRICT, AVFMT_TS_NEGATIVE
20 */
21 int flags;
22
23 /**
24 * List of supported codec_id-codec_tag pairs, ordered by "better
25 * choice first". The arrays are all terminated by AV_CODEC_ID_NONE.
26 */
27 const struct AVCodecTag * const *codec_tag;
28
29
30 const AVClass *priv_class; ///< AVClass for the private context
31
32 /*****************************************************************
33 * No fields below this line are part of the public API. They
34 * may not be used outside of libavformat and can be changed and
35 * removed at will.
36 * New public fields should be added right above.
37 *****************************************************************
38 */
39 struct AVOutputFormat *next;
40 /**
41 * size of private data so that it can be allocated in the wrapper
42 */
43 int priv_data_size;
44
45 int (*write_header)(struct AVFormatContext *);
46 /**
47 * Write a packet. If AVFMT_ALLOW_FLUSH is set in flags,
48 * pkt can be NULL in order to flush data buffered in the muxer.
49 * When flushing, return 0 if there still is more data to flush,
50 * or 1 if everything was flushed and there is no more buffered
51 * data.
52 */
53 int (*write_packet)(struct AVFormatContext *, AVPacket *pkt);
54 int (*write_trailer)(struct AVFormatContext *);
55 /**
56 * Currently only used to set pixel format if not YUV420P.
57 */
58 int (*interleave_packet)(struct AVFormatContext *, AVPacket *out,
59 AVPacket *in, int flush);
60 /**
61 * Test if the given codec can be stored in this container.
62 *
63 * @return 1 if the codec is supported, 0 if it is not.
64 * A negative number if unknown.
65 * MKTAG('A', 'P', 'I', 'C') if the codec is only supported as AV_DISPOSITION_ATTACHED_PIC
66 */
67 int (*query_codec)(enum AVCodecID id, int std_compliance);
68
69 void (*get_output_timestamp)(struct AVFormatContext *s, int stream,
70 int64_t *dts, int64_t *wall);
71 /**
72 * Allows sending messages from application to device.
73 */
74 int (*control_message)(struct AVFormatContext *s, int type,
75 void *data, size_t data_size);
76
77 /**
78 * Write an uncoded AVFrame.
79 *
80 * See av_write_uncoded_frame() for details.
81 *
82 * The library will free *frame afterwards, but the muxer can prevent it
83 * by setting the pointer to NULL.
84 */
85 int (*write_uncoded_frame)(struct AVFormatContext *, int stream_index,
86 AVFrame **frame, unsigned flags);
87 /**
88 * Returns device list with it properties.
89 * @see avdevice_list_devices() for more details.
90 */
91 int (*get_device_list)(struct AVFormatContext *s, struct AVDeviceInfoList *device_list);
92 /**
93 * Initialize device capabilities submodule.
94 * @see avdevice_capabilities_create() for more details.
95 */
96 int (*create_device_capabilities)(struct AVFormatContext *s, struct AVDeviceCapabilitiesQuery *caps);
97 /**
98 * Free device capabilities submodule.
99 * @see avdevice_capabilities_free() for more details.
100 */
101 int (*free_device_capabilities)(struct AVFormatContext *s, struct AVDeviceCapabilitiesQuery *caps);
102 enum AVCodecID data_codec; /**< default data codec */
103 /**
104 * Initialize format. May allocate data here, and set any AVFormatContext or
105 * AVStream parameters that need to be set before packets are sent.
106 * This method must not write output.
107 *
108 * Any allocations made here must be freed in deinit().
109 */
110 int (*init)(struct AVFormatContext *);
111 /**
112 * Deinitialize format. If present, this is called whenever the muxer is being
113 * destroyed, regardless of whether or not the header has been written.
114 *
115 * If a trailer is being written, this is called after write_trailer().
116 *
117 * This is called if init() fails as well.
118 */
119 void (*deinit)(struct AVFormatContext *);
120 /**
121 * Set up any necessary bitstream filtering and extract any extra data needed
122 * for the global header.
123 * Return 0 if more packets from this stream must be checked; 1 if not.
124 */
125 int (*check_bitstream)(struct AVFormatContext *, const AVPacket *pkt);
126 } AVOutputFormat;
3.常见变量及其作用
1 const char *name; 2 const char *long_name;//格式的描述性名称，易于阅读。 3 enum AVCodecID audio_codec; //默认的音频编解码器 4 enum AVCodecID video_codec; //默认的视频编解码器 5 enum AVCodecID subtitle_codec; //默认的字幕编解码器 6 struct AVOutputFormat *next; 7 int (*write_header)(struct AVFormatContext *); 8 int (*write_packet)(struct AVFormatContext *, AVPacket *pkt);//写一个数据包。 如果在标志中设置AVFMT_ALLOW_FLUSH，则pkt可以为NULL。 9 int (*write_trailer)(struct AVFormatContext *); 10 int (*interleave_packet)(struct AVFormatContext *, AVPacket *out, AVPacket *in, int flush); 11 int (*control_message)(struct AVFormatContext *s, int type, void *data, size_t data_size);//允许从应用程序向设备发送消息。 12 int (*write_uncoded_frame)(struct AVFormatContext *, int stream_index, AVFrame **frame, unsigned flags);//写一个未编码的AVFrame。 13 int (*init)(struct AVFormatContext *);//初始化格式。 可以在此处分配数据，并设置在发送数据包之前需要设置的任何AVFormatContext或AVStream参数。 14 void (*deinit)(struct AVFormatContext *);//取消初始化格式。 15 int (*check_bitstream)(struct AVFormatContext *, const AVPacket *pkt);//设置任何必要的比特流过滤，并提取全局头部所需的任何额外数据。
作者：YellowLayne
链接：https://www.jianshu.com/p/4d1629aaba42
来源：简书
著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。 标签：AVFMT,struct,AVFormatContext,int,FFmpeg,codec,data,AVOutputFormat,结构 From： https://www.cnblogs.com/lizishaoye/p/18241462