AVInputFormat 是 FFmpeg 中用于描述输入格式（如文件容器、设备流等）的核心结构体，属于 libavformat 库的一部分。其主要功能是定义解封装（demuxing）过程中如何解析不同格式的输入数据。以下是其关键特性与使用方式的总结：
/**
* @addtogroup lavf_decoding
* @{
*/
typedef struct AVInputFormat {
/**
* A comma separated list of short names for the format. New names
* may be appended with a minor bump.
*/
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;
/**
* Can use flags: AVFMT_NOFILE, AVFMT_NEEDNUMBER, AVFMT_SHOW_IDS,
* AVFMT_NOTIMESTAMPS, AVFMT_GENERIC_INDEX, AVFMT_TS_DISCONT, AVFMT_NOBINSEARCH,
* AVFMT_NOGENSEARCH, AVFMT_NO_BYTE_SEEK, AVFMT_SEEK_TO_PTS.
*/
int flags;
/**
* If extensions are defined, then no probe is done. You should
* usually not use extension format guessing because it is not
* reliable enough
*/
const char *extensions;
const struct AVCodecTag * const *codec_tag;
const AVClass *priv_class; ///< AVClass for the private context
/**
* Comma-separated list of mime types.
* It is used check for matching mime types while probing.
* @see av_probe_input_format2
*/
const char *mime_type;
/*****************************************************************
* 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.
*****************************************************************
*/
ff_const59 struct AVInputFormat *next;
/**
* Raw demuxers store their codec ID here.
*/
int raw_codec_id;
/**
* Size of private data so that it can be allocated in the wrapper.
*/
int priv_data_size;
/**
* Tell if a given file has a chance of being parsed as this format.
* The buffer provided is guaranteed to be AVPROBE_PADDING_SIZE bytes
* big so you do not have to check for that unless you need more.
*/
int (*read_probe)(const AVProbeData *);
/**
* Read the format header and initialize the AVFormatContext
* structure. Return 0 if OK. 'avformat_new_stream' should be
* called to create new streams.
*/
int (*read_header)(struct AVFormatContext *);
/**
* Read one packet and put it in 'pkt'. pts and flags are also
* set. 'avformat_new_stream' can be called only if the flag
* AVFMTCTX_NOHEADER is used and only in the calling thread (not in a
* background thread).
* @return 0 on success, < 0 on error.
* Upon returning an error, pkt must be unreferenced by the caller.
*/
int (*read_packet)(struct AVFormatContext *, AVPacket *pkt);
/**
* Close the stream. The AVFormatContext and AVStreams are not
* freed by this function
*/
int (*read_close)(struct AVFormatContext *);
/**
* Seek to a given timestamp relative to the frames in
* stream component stream_index.
* @param stream_index Must not be -1.
* @param flags Selects which direction should be preferred if no exact
* match is available.
* @return >= 0 on success (but not necessarily the new offset)
*/
int (*read_seek)(struct AVFormatContext *,
int stream_index, int64_t timestamp, int flags);
/**
* Get the next timestamp in stream[stream_index].time_base units.
* @return the timestamp or AV_NOPTS_VALUE if an error occurred
*/
int64_t (*read_timestamp)(struct AVFormatContext *s, int stream_index,
int64_t *pos, int64_t pos_limit);
/**
* Start/resume playing - only meaningful if using a network-based format
* (RTSP).
*/
int (*read_play)(struct AVFormatContext *);
/**
* Pause playing - only meaningful if using a network-based format
* (RTSP).
*/
int (*read_pause)(struct AVFormatContext *);
/**
* Seek to timestamp ts.
* Seeking will be done so that the point from which all active streams
* can be presented successfully will be closest to ts and within min/max_ts.
* Active streams are all streams that have AVStream.discard < AVDISCARD_ALL.
*/
int (*read_seek2)(struct AVFormatContext *s, int stream_index, int64_t min_ts, int64_t ts, int64_t max_ts, int 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);
} AVInputFormat;
/**
* @}
*/1. 结构与字段
AVInputFormat 包含以下核心字段：
- **
name** ：格式的短标识符（如mp4、avfoundation）。 - **
long_name** ：格式的详细描述（如MPEG-4 Part 14）。 - **
extensions** ：支持的文件扩展名（如mp4,mov）。 - **
mime_type** ：关联的 MIME 类型（如video/mp4）。 - 函数指针 ：定义了操作输入格式的方法：
read_probe: 探测输入数据是否匹配当前格式。read_header: 读取文件头信息。read_packet: 读取数据包（如音频/视频帧）。read_close: 关闭输入流并释放资源。
2. 功能与用途
- 格式识别 ：通过
read_probe自动探测输入数据的格式，或在调用avformat_open_input时显式指定。 - 解封装流程：将容器文件（如 MP4）分离为独立的音视频流，供后续解码使用。
- 设备支持 ：不仅支持文件格式，还可处理摄像头、麦克风等设备输入（如 macOS 的
avfoundation）。
3. 使用场景示例
初始化与注册
通过 av_register_all()（旧版本 FFmpeg）注册所有支持的格式，AVInputFormat 实例会以链表形式存储，供后续查找匹配46。
代码片段示例：
cCopy Code
#include <libavformat/avformat.h> int main() { av_register_all(); // 注册格式（旧版本） AVFormatContext *fmt_ctx = avformat_alloc_context(); AVInputFormat *fmt = av_find_input_format("mp4"); // 显式指定格式 avformat_open_input(&fmt_ctx, "input.mp4", fmt, NULL); // ...后续处理 }
自动探测格式
若未指定 AVInputFormat，FFmpeg 会通过 init_input 函数分析文件内容或扩展名，调用匹配的 read_probe 确定格式57。
4. 与其他结构的关联
- AVFormatContext ：上下文对象，存储解封装过程中的状态数据（如流信息、私有数据指针
priv_data）36。 - AVOutputFormat：对应输出格式的结构，用于封装（muxing）流程78。
5. 扩展与定制
开发者可通过自定义 AVInputFormat 实现对新容器格式的支持，需实现探测、读包头、读数据包等函数，并注册到 FFmpeg 的全局链表中6。例如，SRT 字幕格式的解封装器实现中，定义了 srt_read_packet 等函数处理字幕数据包6。
6.那么具体的有哪些 AVInputFormat呢？
static const AVInputFormat * const demuxer_list[] = {
&ff_aa_demuxer,
&ff_aac_demuxer,
&ff_aax_demuxer,
&ff_ac3_demuxer,
&ff_ace_demuxer,
&ff_acm_demuxer,
&ff_act_demuxer,
&ff_adf_demuxer,
&ff_adp_demuxer,
&ff_ads_demuxer,
&ff_adx_demuxer,
&ff_aea_demuxer,
&ff_afc_demuxer,
&ff_aiff_demuxer,
&ff_aix_demuxer,
&ff_alp_demuxer,
&ff_amr_demuxer,
&ff_amrnb_demuxer,
&ff_amrwb_demuxer,
&ff_anm_demuxer,
&ff_apac_demuxer,
&ff_apc_demuxer,
&ff_ape_demuxer,
&ff_apm_demuxer,
&ff_apng_demuxer,
&ff_aptx_demuxer,
&ff_aptx_hd_demuxer,
&ff_aqtitle_demuxer,
&ff_argo_asf_demuxer,
&ff_argo_brp_demuxer,
&ff_argo_cvg_demuxer,
&ff_asf_demuxer,
&ff_asf_o_demuxer,
&ff_ass_demuxer,
&ff_ast_demuxer,
&ff_au_demuxer,
&ff_av1_demuxer,
&ff_avi_demuxer,
&ff_avr_demuxer,
&ff_avs_demuxer,
&ff_avs2_demuxer,
&ff_avs3_demuxer,
&ff_bethsoftvid_demuxer,
&ff_bfi_demuxer,
&ff_bintext_demuxer,
&ff_bink_demuxer,
&ff_binka_demuxer,
&ff_bit_demuxer,
&ff_bitpacked_demuxer,
&ff_bmv_demuxer,
&ff_bfstm_demuxer,
&ff_brstm_demuxer,
&ff_boa_demuxer,
&ff_bonk_demuxer,
&ff_c93_demuxer,
&ff_caf_demuxer,
&ff_cavsvideo_demuxer,
&ff_cdg_demuxer,
&ff_cdxl_demuxer,
&ff_cine_demuxer,
&ff_codec2_demuxer,
&ff_codec2raw_demuxer,
&ff_concat_demuxer,
&ff_data_demuxer,
&ff_daud_demuxer,
&ff_dcstr_demuxer,
&ff_derf_demuxer,
&ff_dfa_demuxer,
&ff_dfpwm_demuxer,
&ff_dhav_demuxer,
&ff_dirac_demuxer,
&ff_dnxhd_demuxer,
&ff_dsf_demuxer,
&ff_dsicin_demuxer,
&ff_dss_demuxer,
&ff_dts_demuxer,
&ff_dtshd_demuxer,
&ff_dv_demuxer,
&ff_dvbsub_demuxer,
&ff_dvbtxt_demuxer,
&ff_dxa_demuxer,
&ff_ea_demuxer,
&ff_ea_cdata_demuxer,
&ff_eac3_demuxer,
&ff_epaf_demuxer,
&ff_ffmetadata_demuxer,
&ff_filmstrip_demuxer,
&ff_fits_demuxer,
&ff_flac_demuxer,
&ff_flic_demuxer,
&ff_flv_demuxer,
&ff_live_flv_demuxer,
&ff_fourxm_demuxer,
&ff_frm_demuxer,
&ff_fsb_demuxer,
&ff_fwse_demuxer,
&ff_g722_demuxer,
&ff_g723_1_demuxer,
&ff_g726_demuxer,
&ff_g726le_demuxer,
&ff_g729_demuxer,
&ff_gdv_demuxer,
&ff_genh_demuxer,
&ff_gif_demuxer,
&ff_gsm_demuxer,
&ff_gxf_demuxer,
&ff_h261_demuxer,
&ff_h263_demuxer,
&ff_h264_demuxer,
&ff_hca_demuxer,
&ff_hcom_demuxer,
&ff_hevc_demuxer,
&ff_hls_demuxer,
&ff_hnm_demuxer,
&ff_ico_demuxer,
&ff_idcin_demuxer,
&ff_idf_demuxer,
&ff_iff_demuxer,
&ff_ifv_demuxer,
&ff_ilbc_demuxer,
&ff_image2_demuxer,
&ff_image2pipe_demuxer,
&ff_image2_alias_pix_demuxer,
&ff_image2_brender_pix_demuxer,
&ff_ingenient_demuxer,
&ff_ipmovie_demuxer,
&ff_ipu_demuxer,
&ff_ircam_demuxer,
&ff_iss_demuxer,
&ff_iv8_demuxer,
&ff_ivf_demuxer,
&ff_ivr_demuxer,
&ff_jacosub_demuxer,
&ff_jv_demuxer,
&ff_kux_demuxer,
&ff_kvag_demuxer,
&ff_laf_demuxer,
&ff_lmlm4_demuxer,
&ff_loas_demuxer,
&ff_luodat_demuxer,
&ff_lrc_demuxer,
&ff_lvf_demuxer,
&ff_lxf_demuxer,
&ff_m4v_demuxer,
&ff_mca_demuxer,
&ff_mcc_demuxer,
&ff_matroska_demuxer,
&ff_mgsts_demuxer,
&ff_microdvd_demuxer,
&ff_mjpeg_demuxer,
&ff_mjpeg_2000_demuxer,
&ff_mlp_demuxer,
&ff_mlv_demuxer,
&ff_mm_demuxer,
&ff_mmf_demuxer,
&ff_mods_demuxer,
&ff_moflex_demuxer,
&ff_mov_demuxer,
&ff_mp3_demuxer,
&ff_mpc_demuxer,
&ff_mpc8_demuxer,
&ff_mpegps_demuxer,
&ff_mpegts_demuxer,
&ff_mpegtsraw_demuxer,
&ff_mpegvideo_demuxer,
&ff_mpjpeg_demuxer,
&ff_mpl2_demuxer,
&ff_mpsub_demuxer,
&ff_msf_demuxer,
&ff_msnwc_tcp_demuxer,
&ff_msp_demuxer,
&ff_mtaf_demuxer,
&ff_mtv_demuxer,
&ff_musx_demuxer,
&ff_mv_demuxer,
&ff_mvi_demuxer,
&ff_mxf_demuxer,
&ff_mxg_demuxer,
&ff_nc_demuxer,
&ff_nistsphere_demuxer,
&ff_nsp_demuxer,
&ff_nsv_demuxer,
&ff_nut_demuxer,
&ff_nuv_demuxer,
&ff_obu_demuxer,
&ff_ogg_demuxer,
&ff_oma_demuxer,
&ff_paf_demuxer,
&ff_pcm_alaw_demuxer,
&ff_pcm_mulaw_demuxer,
&ff_pcm_vidc_demuxer,
&ff_pcm_f64be_demuxer,
&ff_pcm_f64le_demuxer,
&ff_pcm_f32be_demuxer,
&ff_pcm_f32le_demuxer,
&ff_pcm_s32be_demuxer,
&ff_pcm_s32le_demuxer,
&ff_pcm_s24be_demuxer,
&ff_pcm_s24le_demuxer,
&ff_pcm_s16be_demuxer,
&ff_pcm_s16le_demuxer,
&ff_pcm_s8_demuxer,
&ff_pcm_u32be_demuxer,
&ff_pcm_u32le_demuxer,
&ff_pcm_u24be_demuxer,
&ff_pcm_u24le_demuxer,
&ff_pcm_u16be_demuxer,
&ff_pcm_u16le_demuxer,
&ff_pcm_u8_demuxer,
&ff_pjs_demuxer,
&ff_pmp_demuxer,
&ff_pp_bnk_demuxer,
&ff_pva_demuxer,
&ff_pvf_demuxer,
&ff_qcp_demuxer,
&ff_r3d_demuxer,
&ff_rawvideo_demuxer,
&ff_realtext_demuxer,
&ff_redspark_demuxer,
&ff_rka_demuxer,
&ff_rl2_demuxer,
&ff_rm_demuxer,
&ff_roq_demuxer,
&ff_rpl_demuxer,
&ff_rsd_demuxer,
&ff_rso_demuxer,
&ff_rtp_demuxer,
&ff_rtsp_demuxer,
&ff_s337m_demuxer,
&ff_sami_demuxer,
&ff_sap_demuxer,
&ff_sbc_demuxer,
&ff_sbg_demuxer,
&ff_scc_demuxer,
&ff_scd_demuxer,
&ff_sdns_demuxer,
&ff_sdp_demuxer,
&ff_sdr2_demuxer,
&ff_sds_demuxer,
&ff_sdx_demuxer,
&ff_segafilm_demuxer,
&ff_ser_demuxer,
&ff_sga_demuxer,
&ff_shorten_demuxer,
&ff_siff_demuxer,
&ff_simbiosis_imx_demuxer,
&ff_sln_demuxer,
&ff_smacker_demuxer,
&ff_smjpeg_demuxer,
&ff_smush_demuxer,
&ff_sol_demuxer,
&ff_sox_demuxer,
&ff_spdif_demuxer,
&ff_srt_demuxer,
&ff_str_demuxer,
&ff_stl_demuxer,
&ff_subviewer1_demuxer,
&ff_subviewer_demuxer,
&ff_sup_demuxer,
&ff_svag_demuxer,
&ff_svs_demuxer,
&ff_swf_demuxer,
&ff_tak_demuxer,
&ff_tedcaptions_demuxer,
&ff_thp_demuxer,
&ff_threedostr_demuxer,
&ff_tiertexseq_demuxer,
&ff_tmv_demuxer,
&ff_truehd_demuxer,
&ff_tta_demuxer,
&ff_txd_demuxer,
&ff_tty_demuxer,
&ff_ty_demuxer,
&ff_v210_demuxer,
&ff_v210x_demuxer,
&ff_vag_demuxer,
&ff_vc1_demuxer,
&ff_vc1t_demuxer,
&ff_vividas_demuxer,
&ff_vivo_demuxer,
&ff_vmd_demuxer,
&ff_vobsub_demuxer,
&ff_voc_demuxer,
&ff_vpk_demuxer,
&ff_vplayer_demuxer,
&ff_vqf_demuxer,
&ff_w64_demuxer,
&ff_wady_demuxer,
&ff_wavarc_demuxer,
&ff_wav_demuxer,
&ff_wc3_demuxer,
&ff_webm_dash_manifest_demuxer,
&ff_webvtt_demuxer,
&ff_wsaud_demuxer,
&ff_wsd_demuxer,
&ff_wsvqa_demuxer,
&ff_wtv_demuxer,
&ff_wve_demuxer,
&ff_wv_demuxer,
&ff_xa_demuxer,
&ff_xbin_demuxer,
&ff_xmd_demuxer,
&ff_xmv_demuxer,
&ff_xvag_demuxer,
&ff_xwma_demuxer,
&ff_yop_demuxer,
&ff_yuv4mpegpipe_demuxer,
&ff_image_bmp_pipe_demuxer,
&ff_image_cri_pipe_demuxer,
&ff_image_dds_pipe_demuxer,
&ff_image_dpx_pipe_demuxer,
&ff_image_exr_pipe_demuxer,
&ff_image_gem_pipe_demuxer,
&ff_image_gif_pipe_demuxer,
&ff_image_hdr_pipe_demuxer,
&ff_image_j2k_pipe_demuxer,
&ff_image_jpeg_pipe_demuxer,
&ff_image_jpegls_pipe_demuxer,
&ff_image_jpegxl_pipe_demuxer,
&ff_image_pam_pipe_demuxer,
&ff_image_pbm_pipe_demuxer,
&ff_image_pcx_pipe_demuxer,
&ff_image_pfm_pipe_demuxer,
&ff_image_pgmyuv_pipe_demuxer,
&ff_image_pgm_pipe_demuxer,
&ff_image_pgx_pipe_demuxer,
&ff_image_phm_pipe_demuxer,
&ff_image_photocd_pipe_demuxer,
&ff_image_pictor_pipe_demuxer,
&ff_image_png_pipe_demuxer,
&ff_image_ppm_pipe_demuxer,
&ff_image_psd_pipe_demuxer,
&ff_image_qdraw_pipe_demuxer,
&ff_image_qoi_pipe_demuxer,
&ff_image_sgi_pipe_demuxer,
&ff_image_svg_pipe_demuxer,
&ff_image_sunrast_pipe_demuxer,
&ff_image_tiff_pipe_demuxer,
&ff_image_vbn_pipe_demuxer,
&ff_image_webp_pipe_demuxer,
&ff_image_xbm_pipe_demuxer,
&ff_image_xpm_pipe_demuxer,
&ff_image_xwd_pipe_demuxer,
NULL };也就是说，对于不同容器来说或者设备流来说，都有自己对应的 AVInputFormat。
7.那么某一个具体的mp4文件或者aac文件对应的 AVInputFormat如何知道呢？
av_find_input_format(const char *short_name)；方法分析-CSDN博客
我们以mp4 和 aac 文件举例说明：
aac 对应的 AVInputFormat 为：
const AVInputFormat ff_aac_demuxer = {
.name = "aac",
.long_name = NULL_IF_CONFIG_SMALL("raw ADTS AAC (Advanced Audio Coding)"),
.read_probe = adts_aac_probe,
.read_header = adts_aac_read_header,
.read_packet = adts_aac_read_packet,
.flags = AVFMT_GENERIC_INDEX,
.extensions = "aac",
.mime_type = "audio/aac,audio/aacp,audio/x-aac",
.raw_codec_id = AV_CODEC_ID_AAC,
};那么对应的三个方法
read_probe: 探测输入数据是否匹配当前格式。对于aac则调用adts_aac_probe方法read_header: 读取文件头信息。对于aac则调用adts_aac_read_header方法read_packet: 读取数据包（如音频/视频帧）。对于aac则调用adts_aac_read_packet方法
如果要理解 adts_aac_probe，adts_aac_read_header，adts_aac_read_packet这三个方法为什么这么写，就必要要 知道 aac 协议的情况，才能完整理解。从这里也能看出，ffmpeg是多么的强大，它将音视频所有格式的解封装都给开发者打包好了，再开发者不知道具体协议的情况下，调用一个函数就能搞定。
mp4 对应的 AVInputFormat 为：
const AVInputFormat ff_mov_demuxer = {
.name = "mov,mp4,m4a,3gp,3g2,mj2",
.long_name = NULL_IF_CONFIG_SMALL("QuickTime / MOV"),
.priv_class = &mov_class,
.priv_data_size = sizeof(MOVContext),
.extensions = "mov,mp4,m4a,3gp,3g2,mj2,psp,m4b,ism,ismv,isma,f4v,avif",
.flags_internal = FF_FMT_INIT_CLEANUP,
.read_probe = mov_probe,
.read_header = mov_read_header,
.read_packet = mov_read_packet,
.read_close = mov_read_close,
.read_seek = mov_read_seek,
.flags = AVFMT_NO_BYTE_SEEK | AVFMT_SEEK_TO_PTS | AVFMT_SHOW_IDS,
};这个mp4对应的AVInputFormat 是如何找到的呢？一般的想法是从 demuxer_list.c中用眼睛看，有没有mp4之类的关键字，实际上这样是不合适的。
合适的方法是通过 av_find_input_format()
int avinputformat() {
AVInputFormat* input_format = av_find_input_format("mp4");
if (input_format) {
printf("Found input format: %s\n", input_format->name);
cout << "input_format->long_name = " << input_format->long_name<< endl;
//input_format.
}
else {
printf("Input format not found!\n");
}
return 0;
}可以通过打印出来的 short name，long name 等再search ffmpeg 源码，进而找到对应的 解复用器的 具体方法
例如我们 对于mp4打印的信息如下，
Found input format: mov,mp4,m4a,3gp,3g2,mj2
input_format->long_name = QuickTime / MOV
那么就可以在源码中search "mov,mp4,m4a,3gp,3g2,mj2" 关键字，进而找到解复用mp4文件的具体的 AVInputFormat。
const AVInputFormat ff_mov_demuxer = {
.name = "mov,mp4,m4a,3gp,3g2,mj2",
.long_name = NULL_IF_CONFIG_SMALL("QuickTime / MOV"),
.priv_class = &mov_class,
.priv_data_size = sizeof(MOVContext),
.extensions = "mov,mp4,m4a,3gp,3g2,mj2,psp,m4b,ism,ismv,isma,f4v,avif",
.flags_internal = FF_FMT_INIT_CLEANUP,
.read_probe = mov_probe,
.read_header = mov_read_header,
.read_packet = mov_read_packet,
.read_close = mov_read_close,
.read_seek = mov_read_seek,
.flags = AVFMT_NO_BYTE_SEEK | AVFMT_SEEK_TO_PTS | AVFMT_SHOW_IDS,
};同理，如果要知道mp4文件的对应的这些方法 为什么 这么写，就必要要明白 mp4协议，才能理解。
8.从解复用流程上再说明
在解复用文件的时候，会调用如下的如下三个函数
AVFormatContext *avformat_alloc_context(void);
int avformat_open_input(AVFormatContext **ps, const char *url, ff_const59 AVInputFormat*fmt, AVDictionary **options);
int avformat_find_stream_info(AVFormatContext *ic, AVDictionary **options);
在实际开发中，在avformat_open_input函数中，需要传递一个 AVInputFormat ，当我们传递的AVInputFormat 为nullptr时，ffmpeg 在 avformat_open_input源码中是如何知道你要解析的文件，用的是那个具体的 AVInputFormat呢？
参考 avformat_open_input的过程分析，这个哥们很多博客都写的不错。
ffmpeg的avformat_open_input()分析过程--以mp4为例（十）_ffmpeg mp4 avformat-CSDN博客
9. 设备支持 ：从摄像头、麦克风等设备输入（如 macOS 的 avfoundation）。
从前面的学习我们知道，
用于根据输入格式的名称（如 "mp4"、"wav"、"avfoundation" 等）查找对应的输入格式结构体 AVInputFormat。