内容简介:FFmpeg 是一个多媒体框架,能够处理解编码、转码、mux、demux、流、滤镜和播放。它支持很多格式,且具有高度的移植性。
A complete, cross-platform solution to record, convert and stream audio and video.
FFmpeg 是一个多媒体框架,能够处理解编码、转码、mux、demux、流、滤镜和播放。它支持很多格式,且具有高度的移植性。
类库
libavformat
- 用于解析和生成音视频格式
libavcodec
- 编解码音视频
libavutil
- 工具库
libswscale
- 提供比例缩放、色彩映射转换、图像颜色空间或格式转换的功能
libswresample
- 音频重采样,采样格式转换和混合等
libavfilter
- 滤波器,如宽高比裁剪、格式化、非格式化、伸缩
libpostproc
- 后期效果处理,如图像的去块效应等
libavdevice
- 硬件采集、加速、显示
结构体之间关系
-
协议(http, rtsp, rtmp, mms)
AVIOContext,URLProtocol,URLContext 主要存储视音频使用的协议的类型以及状态。URLProtocol 存储输入视音频使用的封装格式;每种协议都对应一个URLProtocol结构 (注意:FFMPEG中文件也被当做一种协议 “file” )
-
封装(flv, avi, rmvb, mp4)
AVFormatContext 主要存储视音频封装格式中包含的信息;AVInputFormat 存储输入视音频使用的封装格式。每种视音频封装格式都对应一个 AVInputFormat 结构
-
编解码(h264, mpeg2, aac, mp3)
每个 AVStream 存储一个视频/音频流的相关数据;每个 AVStream 对应一个 AVCodecContext,存储该视频 / 音频流使用解码方式的相关数据;每个 AVCodecContext 中对应一个 AVCodec,包含该视频/音频对应的解码器。每种解码器都对应一个 AVCodec 结构
-
数据
视频的话,每个结构一般是存一帧 (音频可能有好几帧)
解码前数据:AVPacket;解码后数据:AVFrame
结构体
网络协议
AVIOContext
管理输入输出数据的结构体,
在 avformat_open_input()
中进行初始化
typedef struct AVIOContext{ const AVClass *av_class; unsigned char *buffer; /**< Start of the buffer. */ int buffer_size; /**< Maximum buffer size */ unsigned char *buf_ptr; /**< Current position in the buffer */ unsigned char *buf_end; /**< End of the data */ int (*read_packet)(void *opaque, uint8_t *buf, int buf_size); int (*write_packet)(void *opaque, uint8_t *buf, int buf_size); int64_t (*seek)(void *opaque, int64_t offset, int whence); int64_t pos; /**< position in the file of the current buffer */ int must_flush; /**< true if the next seek should flush */ int eof_reached; /**< true if eof reached */ int write_flag; /**< true if open for writing */ int max_packet_size; unsigned long checksum; unsigned char *checksum_ptr; unsigned long (*update_checksum)(unsigned long checksum, const uint8_t *buf, unsigned int size); int error; /**< contains the error code or 0 if no error happened */ int (*read_pause)(void *opaque, int pause); int64_t (*read_seek)(void *opaque, int stream_index, int64_t timestamp, int flags); int seekable; int64_t maxsize; int direct; int64_t bytes_read; int seek_count; int writeout_count; int orig_buffer_size; int short_seek_threshold; }
- unsigned char *buffer : 缓存开始位置
- int buffer_size : 缓存大小(默认32768)
- unsigned char *buf_ptr : 当前指针读取到的位置
- unsigned char *buf_end : 缓存结束的位置
- void *opaque : URLContext 结构体
在解码的情况下,buffer 用于存储 ffmpeg 读入的数据。例如打开一个视频文件的时候,先把数据从硬盘读入buffer,然后在送给解码器用于解码。
URLProtocol
述了音视频数据传输所使用的协议,每种传输协议 (例如 HTTP、RTMP) 等,都会对应一个 URLProtocol 结构
typedef struct URLProtocol { const char *name; int (*url_open)(URLContext *h, const char *url, int flags); int (*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); struct URLProtocol *next; int (*url_read_pause)(URLContext *h, int pause); int64_t (*url_read_seek)(URLContext *h, int stream_index, int64_t timestamp, int flags); int (*url_get_file_handle)(URLContext *h); int priv_data_size; const AVClass *priv_data_class; int flags; int (*url_check)(URLContext *h, int mask); }
-
const char *name : 存储协议的名称,每一种输入协议都对应这样一个结构体
URLProtocol ff_rtmp_protocol = { .name = "rtmp", .url_open = rtmp_open, .url_read = rtmp_read, .url_write = rtmp_write, .url_close = rtmp_close, .url_read_pause = rtmp_read_pause, .url_read_seek = rtmp_read_seek, .url_get_file_handle = rtmp_get_file_handle, .priv_data_size = sizeof(RTMP), .flags = URL_PROTOCOL_FLAG_NETWORK, };
等号右边的函数是完成具体读写功能的函数。可以看一下 file 协议的几个函数(file.c)
static int file_read(URLContext *h, unsigned char *buf, int size) { int fd = (intptr_t) h->priv_data; int r = read(fd, buf, size); return (-1 == r)?AVERROR(errno):r; } static int file_write(URLContext *h, const unsigned char *buf, int size) { int fd = (intptr_t) h->priv_data; int r = write(fd, buf, size); return (-1 == r)?AVERROR(errno):r; } static int file_get_handle(URLContext *h) { return (intptr_t) h->priv_data; } static int file_check(URLContext *h, int mask) { struct stat st; int ret = stat(h->filename, &st); if (ret < 0) return AVERROR(errno); ret |= st.st_mode&S_IRUSR ? mask&AVIO_FLAG_READ : 0; ret |= st.st_mode&S_IWUSR ? mask&AVIO_FLAG_WRITE : 0; return ret; } #if CONFIG_FILE_PROTOCOL static int file_open(URLContext *h, const char *filename, int flags) { int access; int fd; av_strstart(filename, "file:", &filename); if (flags & AVIO_FLAG_WRITE && flags & AVIO_FLAG_READ) { access = O_CREAT | O_TRUNC | O_RDWR; } else if (flags & AVIO_FLAG_WRITE) { access = O_CREAT | O_TRUNC | O_WRONLY; } else { access = O_RDONLY; } #ifdef O_BINARY access |= O_BINARY; #endif fd = open(filename, access, 0666); if (fd == -1) return AVERROR(errno); h->priv_data = (void *) (intptr_t) fd; return 0; } /* XXX: use llseek */ static int64_t file_seek(URLContext *h, int64_t pos, int whence) { int fd = (intptr_t) h->priv_data; if (whence == AVSEEK_SIZE) { struct stat st; int ret = fstat(fd, &st); return ret < 0 ? AVERROR(errno) : st.st_size; } return lseek(fd, pos, whence); } static int file_close(URLContext *h) { int fd = (intptr_t) h->priv_data; return close(fd); }
URLContext
封装了协议对象及协议操作对象
封装格式
AVFormatContext
描述了媒体文件的构成及基本信息,是统领全局的基本结构体,贯穿程序始终,很多函数都要用它作为参数
typedef struct AVFormatContext { const AVClass *av_class; struct AVInputFormat *iformat; struct AVOutputFormat *oformat; void *priv_data; AVIOContext *pb; int ctx_flags; unsigned int nb_streams; AVStream **streams; char filename[1024]; int64_t start_time; int64_t duration; int bit_rate; unsigned int packet_size; int max_delay; int flags; const uint8_t *key; int keylen; unsigned int nb_programs; AVProgram **programs; enum AVCodecID video_codec_id; enum AVCodecID audio_codec_id; enum AVCodecID subtitle_codec_id; unsigned int max_index_size; unsigned int max_picture_buffer; unsigned int nb_chapters; AVChapter **chapters; AVDictionary *metadata; int64_t start_time_realtime; int fps_probe_size; int error_recognition; AVIOInterruptCB interrupt_callback; int64_t max_interleave_delta; int strict_std_compliance; int event_flags; int max_ts_probe; int avoid_negative_ts; int ts_id; int audio_preload; int max_chunk_duration; int max_chunk_size; int use_wallclock_as_timestamps; int avio_flags; enum AVDurationEstimationMethod duration_estimation_method; int64_t skip_initial_bytes; unsigned int correct_ts_overflow; int seek2any; int probe_score; int format_probesize; char *codec_whitelist; char *format_whitelist; AVFormatInternal *internal; int io_repositioned; AVCodec *video_codec; AVCodec *audio_codec; AVCodec *subtitle_codec; AVCodec *data_codec; int metadata_header_padding; void *opaque; av_format_control_message control_message_cb; int64_t output_ts_offset; uint8_t *dump_separator; enum AVCodecID data_codec_id; int (*open_cb)(struct AVFormatContext *s, AVIOContext **p, const char *url, int flags, const AVIOInterruptCB *int_cb, AVDictionary **options); }
-
struct AVInputFormat *iformat : 输入数据的封装格式,由
avformat_open_input
设置,仅仅在 Demuxing 使用。 -
struct AVOutputFormat *oformat : 输出数据的封装格式,必须由使用者在
avformat_write_header
前设置,由 Muxing 使用 -
priv_data : 在 muxing 中,由
avformat_write_header
设置;在 demuxing 中,由avformat_open_input
设置 -
AVIOContext *pb : 输入数据的缓存。如 果
iformat/oformat.flags
设置为AVFMT_NOFILE
的话,该字段不需要设置。对于 Demuxing ,需要在avformat_open_input
前设置,或由avformat_open_input
设置;对于 Muxing,在avformat_write_header
前设置 -
ctx_flags : 码流的信息,表明码流属性的的信号。由
libavformat
设置,例如AVFMTCTX_NOHEADER
-
nb_streams : 指
AVFormatContext.streams
的数量,必须由avformat_new_stream
设置 -
AVStream **streams : 文件中所有码流的列表,新的码流创建使用
avformat_new_stream
函数。Demuxing 中,码流由avformat_open_input
创建。 如果AVFMTCTX_NOHEADER
被设置,新的码流可以出现在av_read_frame
中。Muxing 中,码流在avformat_write_header
之前由用户创建,它的释放是由avformat_free_context
完成的 -
filename : 输入或输出的文件名,Demuxing 中由
avformat_open_input
设置,Muxing 中在使用avformat_write_header
前由调用者设置 - int64_t duration : 码流的时长
- bit_rate : 比特率
-
AVDictionary *metadata : 元数据,适用于整个文件。通过
av_dict_get()
函数获得视频的原数据
AVInputFormat
解复用器对象,每种作为输入的封装格式 (例如 FLV 、 MP4 、 TS 等) 对应一个该结构体
AVOutputFormat
复用器对象,每种作为输出的封装格式(例如 FLV , MP4 、 TS 等)对应一个该结构体
AVStream
用于描述一个视频 / 音频流的相关数据信息
编解码
AVCodecContext
描述编解码器上下文的数据结构,包含了众多编解码器需要的参数信息
typedef struct AVCodecContext{ const AVClass *av_class; int log_level_offset; enum AVMediaType codec_type; const struct AVCodec *codec; enum AVCodecID codec_id; unsigned int codec_tag; void *priv_data; struct AVCodecInternal *internal; void *opaque; int bit_rate; int bit_rate_tolerance; int global_quality; int compression_level; int flags; int flags2; uint8_t *extradata; int extradata_size; AVRational time_base; int ticks_per_frame; int delay; int width, height; int coded_width, coded_height; int gop_size; enum AVPixelFormat pix_fmt; void (*draw_horiz_band)(struct AVCodecContext *s, const AVFrame *src, int offset[AV_NUM_DATA_POINTERS], int y, int type, int height); enum AVPixelFormat (*get_format)(struct AVCodecContext *s, const enum AVPixelFormat * fmt); int max_b_frames; float b_quant_factor; int b_frame_strategy; float b_quant_offset; int has_b_frames; int mpeg_quant; /*decoding: unused*/ float i_quant_factor; /*decoding: unused*/ float i_quant_offset; /*decoding: unused*/ float lumi_masking; /*decoding: unused*/ float temporal_cplx_masking; /*decoding: unused*/ float spatial_cplx_masking; /*decoding: unused*/ float p_masking; /*decoding: unused*/ float dark_masking; /*decoding: unused*/ int slice_count; int prediction_method; /*decoding: unused*/ int *slice_offset; AVRational sample_aspect_ratio; int me_cmp; /*decoding: unused*/ int me_sub_cmp; /*decoding: unused*/ int mb_cmp; /*decoding: unused*/ ... }AVCodecContext;
- AVMediaType codec_type : 编解码器的类型,如音频、视频、字幕
- AVCdec *codec : 采用的解码器 AVCodec
- int bit_rate : 平均比特率
- uint8_t *extradata; int extradata_size : 针对特定编码器包含的附加信息(例如对于H.264解码器来说,存储SPS,PPS等)
- AVRational time_base : 根据该参数,可以把PTS转化为实际的时间(单位为秒s)
- int width, height : 视频的宽高
- int refs : 运动估计参考帧的个数
- int sample_rate : 采样率
- int channels : 声道数
- enum AVSampleFormat sample_fmt : 采样格式
- int profile : 型(H.264里面就有,其他编码标准应该也有)
- int level : 级(和profile差不太多)
AVCodecContext 使用 avcodec_alloc_context3 分配,该函数除了分配 AVCodecContext 外,还会初始化默认的字段。分配的内存必须通过 avcodec_free_context 释放。 AVCodecContext 中很多的参数是编码的时候使用的,而不是解码的时候使用的
avcodec_register_all(); ... codec = avcodec_find_decoder(AV_CODEC_ID_H264); if(!codec) exit(1); context = avcodec_alloc_context3(codec); if(avcodec_open2(context, codec, opts) < 0) exit(1);
codec_type(编解码器类型)
enum AVMediaType { AVMEDIA_TYPE_UNKNOWN = -1, ///< Usually treated as AVMEDIA_TYPE_DATA AVMEDIA_TYPE_VIDEO, AVMEDIA_TYPE_AUDIO, AVMEDIA_TYPE_DATA, ///< Opaque data information usually continuous AVMEDIA_TYPE_SUBTITLE, AVMEDIA_TYPE_ATTACHMENT, ///< Opaque data information usually sparse AVMEDIA_TYPE_NB };
sample_fmt(音频采样格式)
enum AVSampleFormat { AV_SAMPLE_FMT_NONE = -1, AV_SAMPLE_FMT_U8, ///< unsigned 8 bits AV_SAMPLE_FMT_S16, ///< signed 16 bits AV_SAMPLE_FMT_S32, ///< signed 32 bits AV_SAMPLE_FMT_FLT, ///< float AV_SAMPLE_FMT_DBL, ///< double AV_SAMPLE_FMT_U8P, ///< unsigned 8 bits, planar AV_SAMPLE_FMT_S16P, ///< signed 16 bits, planar AV_SAMPLE_FMT_S32P, ///< signed 32 bits, planar AV_SAMPLE_FMT_FLTP, ///< float, planar AV_SAMPLE_FMT_DBLP, ///< double, planar AV_SAMPLE_FMT_NB ///< Number of sample formats. DO NOT USE if linking dynamically };
profile
#define FF_PROFILE_UNKNOWN -99 #define FF_PROFILE_RESERVED -100 #define FF_PROFILE_AAC_MAIN 0 #define FF_PROFILE_AAC_LOW 1 #define FF_PROFILE_AAC_SSR 2 #define FF_PROFILE_AAC_LTP 3 #define FF_PROFILE_AAC_HE 4 #define FF_PROFILE_AAC_HE_V2 28 #define FF_PROFILE_AAC_LD 22 #define FF_PROFILE_AAC_ELD 38 #define FF_PROFILE_DTS 20 #define FF_PROFILE_DTS_ES 30 #define FF_PROFILE_DTS_96_24 40 #define FF_PROFILE_DTS_HD_HRA 50 #define FF_PROFILE_DTS_HD_MA 60 #define FF_PROFILE_MPEG2_422 0 #define FF_PROFILE_MPEG2_HIGH 1 #define FF_PROFILE_MPEG2_SS 2 #define FF_PROFILE_MPEG2_SNR_SCALABLE 3 #define FF_PROFILE_MPEG2_MAIN 4 #define FF_PROFILE_MPEG2_SIMPLE 5 #define FF_PROFILE_H264_CONSTRAINED (1<<9) // 8+1; constraint_set1_flag #define FF_PROFILE_H264_INTRA (1<<11) // 8+3; constraint_set3_flag #define FF_PROFILE_H264_BASELINE 66 #define FF_PROFILE_H264_CONSTRAINED_BASELINE (66|FF_PROFILE_H264_CONSTRAINED) #define FF_PROFILE_H264_MAIN 77 #define FF_PROFILE_H264_EXTENDED 88 #define FF_PROFILE_H264_HIGH 100 #define FF_PROFILE_H264_HIGH_10 110 #define FF_PROFILE_H264_HIGH_10_INTRA (110|FF_PROFILE_H264_INTRA) #define FF_PROFILE_H264_HIGH_422 122 #define FF_PROFILE_H264_HIGH_422_INTRA (122|FF_PROFILE_H264_INTRA) #define FF_PROFILE_H264_HIGH_444 144 #define FF_PROFILE_H264_HIGH_444_PREDICTIVE 244 #define FF_PROFILE_H264_HIGH_444_INTRA (244|FF_PROFILE_H264_INTRA) #define FF_PROFILE_H264_CAVLC_444 44 #define FF_PROFILE_VC1_SIMPLE 0 #define FF_PROFILE_VC1_MAIN 1 #define FF_PROFILE_VC1_COMPLEX 2 #define FF_PROFILE_VC1_ADVANCED 3 #define FF_PROFILE_MPEG4_SIMPLE 0 #define FF_PROFILE_MPEG4_SIMPLE_SCALABLE 1 #define FF_PROFILE_MPEG4_CORE 2 #define FF_PROFILE_MPEG4_MAIN 3 #define FF_PROFILE_MPEG4_N_BIT 4 #define FF_PROFILE_MPEG4_SCALABLE_TEXTURE 5 #define FF_PROFILE_MPEG4_SIMPLE_FACE_ANIMATION 6 #define FF_PROFILE_MPEG4_BASIC_ANIMATED_TEXTURE 7 #define FF_PROFILE_MPEG4_HYBRID 8 #define FF_PROFILE_MPEG4_ADVANCED_REAL_TIME 9 #define FF_PROFILE_MPEG4_CORE_SCALABLE 10 #define FF_PROFILE_MPEG4_ADVANCED_CODING 11 #define FF_PROFILE_MPEG4_ADVANCED_CORE 12 #define FF_PROFILE_MPEG4_ADVANCED_SCALABLE_TEXTURE 13 #define FF_PROFILE_MPEG4_SIMPLE_STUDIO 14 #define FF_PROFILE_MPEG4_ADVANCED_SIMPLE 15
AVCodec
编解码器对象,每种编解码格式 (例如 H.264、AAC 等)对应一个该结构体;每个 AVCodecContext 中含有一个 AVCodec
typedef struct AVCodec{ const char *name; const char *long_name; enum AVMediaType type; enum AVCodecID id; int capabilities; const AVRational *supported_framerates; ///< array of supported framerates, or NULL if any, array is terminated by {0,0} const enum AVPixelFormat *pix_fmts; ///< array of supported pixel formats, or NULL if unknown, array is terminated by -1 const int *supported_samplerates; ///< array of supported audio samplerates, or NULL if unknown, array is terminated by 0 const enum AVSampleFormat *sample_fmts; ///< array of supported sample formats, or NULL if unknown, array is terminated by -1 const uint64_t *channel_layouts; ///< array of support channel layouts, or NULL if unknown. array is terminated by 0 uint8_t max_lowres; ///< maximum value for lowres supported by the decoder, no direct access, use av_codec_get_max_lowres() const AVClass *priv_class; ///< AVClass for the private context const AVProfile *profiles; ///< array of recognized profiles, or NULL if unknown, array is terminated by {FF_PROFILE_UNKNOWN} int priv_data_size; struct AVCodec *next; int (*init_thread_copy)(AVCodecContext *); int (*update_thread_context)(AVCodecContext *dst, const AVCodecContext *src); const AVCodecDefault *defaults; void (*init_static_data)(struct AVCodec *codec); int (*init)(AVCodecContext *); int (*encode_sub)(AVCodecContext *, uint8_t *buf, int buf_size, int (*encode2)(AVCodecContext *avctx, AVPacket *avpkt, const AVFrame *frame, int *got_packet_ptr); int (*decode)(AVCodecContext *, void *outdata, int *outdata_size, AVPacket *avpkt); int (*close)(AVCodecContext *); void (*flush)(AVCodecContext *); int caps_internal; }
- name : 具体的 CODEC 的名称的简短描述,比如 “HEVC”/“H264” 等
- long_name : CODEC 名称的详细描述,比如 “HEVC (High Efficiency Video Coding)”
- type : 媒体类型的字段,它是 enum 型的,表示视频、音频、字幕等,比如AVMEDIA_TYPE_VIDEO、AVMEIDA_TYPE_AUDIO
- id : 唯一标识的 CODEC 类型,比如 AV_CODEC_ID_HEVC
- supported_framerates : 支持的视频帧率的数组,以{0,0}作为结束
- pix_fmts : 编解码器支持的图像格式的数组,以 -1 作为结束
- profiles : 编解码器支持的 Profile,以 HEVC 为例,包含 “Main” / “Main10” / “Main Still Picture”
- supported_samplerates : 支持的音频采样率
- sample_fmts : 支持的音频采样格式
- channel_layouts : 支持的音频声道数
- priv_data_size : 私有数据的大小
enum AVMediaType type
enum AVMediaType { AVMEDIA_TYPE_UNKNOWN = -1, ///< Usually treated as AVMEDIA_TYPE_DATA AVMEDIA_TYPE_VIDEO, AVMEDIA_TYPE_AUDIO, AVMEDIA_TYPE_DATA, ///< Opaque data information usually continuous AVMEDIA_TYPE_SUBTITLE, AVMEDIA_TYPE_ATTACHMENT, ///< Opaque data information usually sparse AVMEDIA_TYPE_NB }
enum AVCodecID id
enum AVCodecID { AV_CODEC_ID_NONE, /* video codecs */ AV_CODEC_ID_MPEG1VIDEO, AV_CODEC_ID_MPEG2VIDEO, ///< preferred ID for MPEG-1/2 video decoding AV_CODEC_ID_MPEG2VIDEO_XVMC, AV_CODEC_ID_H261, AV_CODEC_ID_H263, AV_CODEC_ID_RV10, AV_CODEC_ID_RV20, AV_CODEC_ID_MJPEG, AV_CODEC_ID_MJPEGB, AV_CODEC_ID_LJPEG, AV_CODEC_ID_SP5X, AV_CODEC_ID_JPEGLS, AV_CODEC_ID_MPEG4, AV_CODEC_ID_RAWVIDEO, AV_CODEC_ID_MSMPEG4V1, AV_CODEC_ID_MSMPEG4V2, AV_CODEC_ID_MSMPEG4V3, AV_CODEC_ID_WMV1, AV_CODEC_ID_WMV2, AV_CODEC_ID_H263P, AV_CODEC_ID_H263I, AV_CODEC_ID_FLV1, AV_CODEC_ID_SVQ1, AV_CODEC_ID_SVQ3, AV_CODEC_ID_DVVIDEO, AV_CODEC_ID_HUFFYUV, AV_CODEC_ID_CYUV, AV_CODEC_ID_H264, ... }
const enum AVPixelFormat *pix_fmts
enum AVPixelFormat { AV_PIX_FMT_NONE = -1, AV_PIX_FMT_YUV420P, ///< planar YUV 4:2:0, 12bpp, (1 Cr & Cb sample per 2x2 Y samples) AV_PIX_FMT_YUYV422, ///< packed YUV 4:2:2, 16bpp, Y0 Cb Y1 Cr AV_PIX_FMT_RGB24, ///< packed RGB 8:8:8, 24bpp, RGBRGB... AV_PIX_FMT_BGR24, ///< packed RGB 8:8:8, 24bpp, BGRBGR... AV_PIX_FMT_YUV422P, ///< planar YUV 4:2:2, 16bpp, (1 Cr & Cb sample per 2x1 Y samples) AV_PIX_FMT_YUV444P, ///< planar YUV 4:4:4, 24bpp, (1 Cr & Cb sample per 1x1 Y samples) AV_PIX_FMT_YUV410P, ///< planar YUV 4:1:0, 9bpp, (1 Cr & Cb sample per 4x4 Y samples) AV_PIX_FMT_YUV411P, ///< planar YUV 4:1:1, 12bpp, (1 Cr & Cb sample per 4x1 Y samples) AV_PIX_FMT_GRAY8, ///< Y , 8bpp AV_PIX_FMT_MONOWHITE, ///< Y , 1bpp, 0 is white, 1 is black, in each byte pixels are ordered from the msb to the lsb AV_PIX_FMT_MONOBLACK, ///< Y , 1bpp, 0 is black, 1 is white, in each byte pixels are ordered from the msb to the lsb AV_PIX_FMT_PAL8, ///< 8 bit with PIX_FMT_RGB32 palette AV_PIX_FMT_YUVJ420P, ///< planar YUV 4:2:0, 12bpp, full scale (JPEG), deprecated in favor of PIX_FMT_YUV420P and setting color_range AV_PIX_FMT_YUVJ422P, ///< planar YUV 4:2:2, 16bpp, full scale (JPEG), deprecated in favor of PIX_FMT_YUV422P and setting color_range AV_PIX_FMT_YUVJ444P, ///< planar YUV 4:4:4, 24bpp, full scale (JPEG), deprecated in favor of PIX_FMT_YUV444P and setting color_range AV_PIX_FMT_XVMC_MPEG2_MC,///< XVideo Motion Acceleration via common packet passing AV_PIX_FMT_XVMC_MPEG2_IDCT, ... }
const enum AVSampleFormat *sample_fmts
enum AVSampleFormat { AV_SAMPLE_FMT_NONE = -1, AV_SAMPLE_FMT_U8, ///< unsigned 8 bits AV_SAMPLE_FMT_S16, ///< signed 16 bits AV_SAMPLE_FMT_S32, ///< signed 32 bits AV_SAMPLE_FMT_FLT, ///< float AV_SAMPLE_FMT_DBL, ///< double AV_SAMPLE_FMT_U8P, ///< unsigned 8 bits, planar AV_SAMPLE_FMT_S16P, ///< signed 16 bits, planar AV_SAMPLE_FMT_S32P, ///< signed 32 bits, planar AV_SAMPLE_FMT_FLTP, ///< float, planar AV_SAMPLE_FMT_DBLP, ///< double, planar AV_SAMPLE_FMT_NB ///< Number of sample formats. DO NOT USE if linking dynamically };
每一个编解码器对应一个 AVCodec 该结构体
AVCodec ff_h264_decoder = { .name = "h264", .type = AVMEDIA_TYPE_VIDEO, .id = CODEC_ID_H264, .priv_data_size = sizeof(H264Context), .init = ff_h264_decode_init, .close = ff_h264_decode_end, .decode = decode_frame, .capabilities = /*CODEC_CAP_DRAW_HORIZ_BAND |*/ CODEC_CAP_DR1 | CODEC_CAP_DELAY | CODEC_CAP_SLICE_THREADS | CODEC_CAP_FRAME_THREADS, .flush= flush_dpb, .long_name = NULL_IF_CONFIG_SMALL("H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10"), .init_thread_copy = ONLY_IF_THREADS_ENABLED(decode_init_thread_copy), .update_thread_context = ONLY_IF_THREADS_ENABLED(decode_update_thread_context), .profiles = NULL_IF_CONFIG_SMALL(profiles), .priv_class = &h264_class, };
AVCodecParameters
编解码参数,每个 AVStream 中都含有一个 AVCodecParameters,用来存放当前流的编解码参数
数据
AVPacket
存放编码后、解码前的压缩数据,即 ES 数据
typedef struct AVPacket{ AVBufferRef *buf; int64_t pts; int64_t dts; uint8_t *data; int size; int stream_index; int flags; AVPacketSideData *side_data; int side_data_elems; int duration; int64_t pos; int64_t convergence_duration; }
- pts: 显示时间戳,它的单位是 AVStream->time_base;如果在文件中没有保存这个值,它被设置为 AV_NOPTS_VALUE。由于图像显示不可能早于图像解压,因此 PTS 必须比 DTS(解码时间戳)大或者相等。某些文件格式中可能会使用 PTS/DTS 表示其他含义,此时时间戳必须转为真正的时间戳才能保存到 AVPacket 结构中
- dts : 解码时间戳,它的单位是 AVStream->time_base,表示压缩视频解码的时间,如果文件中没有保存该值,它被设置为 AV_NOPTS_VALUE
- data : 指向真正的压缩编码的数据
- size : 表示该 AVPacket 结构中 data 字段所指向的压缩数据的大小
- stream_index : 标识该 AVPacket 结构所属的视频流或音频流
- duration : 该 AVPacket 包以 AVStream->time_base 为单位,所持续的时间,0 表示未知,或者为显示时间戳的差值(next_pts - this pts)
- pos : 表示该 AVPacket 数据在媒体中的位置,即字节偏移量
AVFrame
存放编码前、解码后的原始数据,如 YUV 格式的视频数据或 PCM 格式的音频数据等
AVFrame 结构体必须使用 av_frame_alloc()
分配,注意该函数只是分配了 AVFrame 结构本身,它的 data 区域要用其他方式管理;该结构体的释放要用 av_frame_free()
。
AVFrame 结构体通常只需分配一次,之后即可通过保存不同的数据来重复多次使用,比如一个 AVFrame 结构可以保存从解码器中解码出的多帧数据。此时,就可以使用 av_frame_unref()
释放任何由 Frame 保存的参考帧并还原回最原始的状态。
typedef struct AVFrame{ uint8_t *data[AV_NUM_DATA_POINTERS]; int linesize[AV_NUM_DATA_POINTERS]; uint8_t **extended_data; int width, height; int nb_samples; /* number of audio samples(per channel) described by this frame */ int format; int key_frame; /* 1->keyframe, 0->not*/ enum AVPictureType pict_type; AVRational sample_aspect_ratio; int64_t pts; int64_t pkt_pts; int64_t pkt_dts; int coded_picture_number; int display_picture_number; int quality; void *opaque; /* for some private data of the user */ uint64_t error[AV_NUM_DATA_POINTERS]; int repeat_pict; int interlaced_frame; int top_field_first; /* If the content is interlaced, is top field displayed first */ int palette_has_changed; int64_t reordered_opaque; int sample_rate; /*Sample rate of the audio data*/ uint64_t channel_layout; /*channel layout of the audio data*/ AVBufferRef *buf[AV_NUM_DATA_POINTERS]; AVBufferRef **extended_buf; int nb_exteneded_buf; AVFrameSideData **side_data; int nb_side_data; int flags; enum AVColorRange color_range; enum AVColorPrimaries color_primaries; enum AVColorTransferCharacteristic color_trc; enum AVColorSpace colorspace; enum AVChromaLocation chroma_location; int64_t best_effort_timestamp; int64_t pkt_pos; int64_t pkt_duration; AVDictionary *metadata; int decode _error_flags; int channels; int pkt_size; AVBufferRef *qp_table_buf; }
avcodec_align_dimensions2()
pict_type
enum AVPictureType { AV_PICTURE_TYPE_NONE = 0, ///< Undefined AV_PICTURE_TYPE_I, ///< Intra AV_PICTURE_TYPE_P, ///< Predicted AV_PICTURE_TYPE_B, ///< Bi-dir predicted AV_PICTURE_TYPE_S, ///< S(GMC)-VOP MPEG4 AV_PICTURE_TYPE_SI, ///< Switching Intra AV_PICTURE_TYPE_SP, ///< Switching Predicted AV_PICTURE_TYPE_BI, ///< BI type };
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