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FFmpeg源代码简单分析#xff1a;常见结构体的初始化和销毁#xff08;AVFormatContext#xff0c;AVFrame等#xff09;_雷霄骅的博客-CSDN博客
结构体
AVFormatContext#xff1a;统领全局的基本结构体。主要用于处理封装格式#xff08;FLV/MKV/RMVB等常见结构体的初始化和销毁AVFormatContextAVFrame等_雷霄骅的博客-CSDN博客
结构体
AVFormatContext统领全局的基本结构体。主要用于处理封装格式FLV/MKV/RMVB等 FFmpeg: AVFormatContext Struct ReferenceAVIOContext输入输出对应的结构体用于输入输出读写文件RTMP协议等 FFmpeg: AVIOContext Struct ReferenceAVStream视音频流对应的结构体 FFmpeg: AVStream Struct ReferenceAVCodecContext音视频编解码结构体 FFmpeg: AVCodecContext Struct ReferenceAVFrame存储非压缩的数据视频对应RGB/YUV像素数据音频对应PCM采样数据 https://ffmpeg.org/doxygen/trunk/structAVFrame.htmlAVPacket存储压缩数据视频对应H.264等码流数据音频对应AAC/MP3等码流数据 https://ffmpeg.org/doxygen/trunk/structAVPacket.html
结构体初始化销毁AVFormatContextavformat_alloc_contextavformat_free_contextAVIOContextavio_alloc_contextavio_context_freeAVStreamavformat_new_streamavformat_free_contextAVCodecContextavcodec_alloc_context3avcodec_free_contextAVPacket av_init_packet() av_new_packet av_packet_freeAVFrame av_frame_alloc av_image_fill_arrays av_frame_free
初始化
avformat_alloc_context() FFmpeg: Core functions
AVFormatContext *avformat_alloc_context(void)
{FFFormatContext *const si av_mallocz(sizeof(*si));AVFormatContext *s;if (!si)return NULL;s si-pub;s-av_class av_format_context_class;s-io_open io_open_default;s-io_close ff_format_io_close_default;s-io_close2 io_close2_default;av_opt_set_defaults(s);si-pkt av_packet_alloc();si-parse_pkt av_packet_alloc();if (!si-pkt || !si-parse_pkt) {avformat_free_context(s);return NULL;}si-shortest_end AV_NOPTS_VALUE;return s;
} 使用av_opt_set_defaults函数给字段设置默认值
void av_opt_set_defaults(void *s)
{av_opt_set_defaults2(s, 0, 0);
}void av_opt_set_defaults2(void *s, int mask, int flags)
{const AVOption *opt NULL;while ((opt av_opt_next(s, opt))) {void *dst ((uint8_t*)s) opt-offset;if ((opt-flags mask) ! flags)continue;if (opt-flags AV_OPT_FLAG_READONLY)continue;switch (opt-type) {case AV_OPT_TYPE_CONST:/* Nothing to be done here */break;case AV_OPT_TYPE_BOOL:case AV_OPT_TYPE_FLAGS:case AV_OPT_TYPE_INT:case AV_OPT_TYPE_INT64:case AV_OPT_TYPE_UINT64:case AV_OPT_TYPE_DURATION:
#if FF_API_OLD_CHANNEL_LAYOUT
FF_DISABLE_DEPRECATION_WARNINGScase AV_OPT_TYPE_CHANNEL_LAYOUT:
FF_ENABLE_DEPRECATION_WARNINGS
#endifcase AV_OPT_TYPE_PIXEL_FMT:case AV_OPT_TYPE_SAMPLE_FMT:write_number(s, opt, dst, 1, 1, opt-default_val.i64);break;case AV_OPT_TYPE_DOUBLE:case AV_OPT_TYPE_FLOAT: {double val;val opt-default_val.dbl;write_number(s, opt, dst, val, 1, 1);}break;case AV_OPT_TYPE_RATIONAL: {AVRational val;val av_d2q(opt-default_val.dbl, INT_MAX);write_number(s, opt, dst, 1, val.den, val.num);}break;case AV_OPT_TYPE_COLOR:set_string_color(s, opt, opt-default_val.str, dst);break;case AV_OPT_TYPE_STRING:set_string(s, opt, opt-default_val.str, dst);break;case AV_OPT_TYPE_IMAGE_SIZE:set_string_image_size(s, opt, opt-default_val.str, dst);break;case AV_OPT_TYPE_VIDEO_RATE:set_string_video_rate(s, opt, opt-default_val.str, dst);break;case AV_OPT_TYPE_BINARY:set_string_binary(s, opt, opt-default_val.str, dst);break;case AV_OPT_TYPE_CHLAYOUT:set_string_channel_layout(s, opt, opt-default_val.str, dst);break;case AV_OPT_TYPE_DICT:set_string_dict(s, opt, opt-default_val.str, dst);break;default:av_log(s, AV_LOG_DEBUG, AVOption type %d of option %s not implemented yet\n,opt-type, opt-name);}}
}avio_alloc_context() FFmpeg: libavformat/avio.h File Reference使用av_malloc为FFIOContest进行内存分配再次调用ffio_init_context完成初始化
AVIOContext *avio_alloc_context(unsigned char *buffer,int buffer_size,int write_flag,void *opaque,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))
{FFIOContext *s av_malloc(sizeof(*s));if (!s)return NULL;ffio_init_context(s, buffer, buffer_size, write_flag, opaque,read_packet, write_packet, seek);return s-pub;
} ffio_init_context对FFIOContest中的缓存函数指针等等进行了赋值
void ffio_init_context(FFIOContext *ctx,unsigned char *buffer,int buffer_size,int write_flag,void *opaque,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))
{AVIOContext *const s ctx-pub;memset(ctx, 0, sizeof(*ctx));s-buffer buffer;ctx-orig_buffer_size s-buffer_size buffer_size;s-buf_ptr buffer;s-buf_ptr_max buffer;s-opaque opaque;s-direct 0;url_resetbuf(s, write_flag ? AVIO_FLAG_WRITE : AVIO_FLAG_READ);s-write_packet write_packet;s-read_packet read_packet;s-seek seek;s-pos 0;s-eof_reached 0;s-error 0;s-seekable seek ? AVIO_SEEKABLE_NORMAL : 0;s-min_packet_size 0;s-max_packet_size 0;s-update_checksum NULL;ctx-short_seek_threshold SHORT_SEEK_THRESHOLD;if (!read_packet !write_flag) {s-pos buffer_size;s-buf_end s-buffer buffer_size;}s-read_pause NULL;s-read_seek NULL;s-write_data_type NULL;s-ignore_boundary_point 0;ctx-current_type AVIO_DATA_MARKER_UNKNOWN;ctx-last_time AV_NOPTS_VALUE;ctx-short_seek_get NULL;
#if FF_API_AVIOCONTEXT_WRITTEN
FF_DISABLE_DEPRECATION_WARNINGSs-written 0;
FF_ENABLE_DEPRECATION_WARNINGS
#endif
}
avformat_new_stream() FFmpeg: Core functions
AVStream *avformat_new_stream(AVFormatContext *s, const AVCodec *c)
{FFFormatContext *const si ffformatcontext(s);FFStream *sti;AVStream *st;AVStream **streams;if (s-nb_streams s-max_streams) {av_log(s, AV_LOG_ERROR, Number of streams exceeds max_streams parameter (%d), see the documentation if you wish to increase it\n,s-max_streams);return NULL;}streams av_realloc_array(s-streams, s-nb_streams 1, sizeof(*streams));if (!streams)return NULL;s-streams streams;sti av_mallocz(sizeof(*sti));if (!sti)return NULL;st sti-pub;#if FF_API_AVSTREAM_CLASSst-av_class stream_class;
#endifst-codecpar avcodec_parameters_alloc();if (!st-codecpar)goto fail;sti-avctx avcodec_alloc_context3(NULL);if (!sti-avctx)goto fail;if (s-iformat) {sti-info av_mallocz(sizeof(*sti-info));if (!sti-info)goto fail;#if FF_API_R_FRAME_RATEsti-info-last_dts AV_NOPTS_VALUE;
#endifsti-info-fps_first_dts AV_NOPTS_VALUE;sti-info-fps_last_dts AV_NOPTS_VALUE;/* default pts setting is MPEG-like */avpriv_set_pts_info(st, 33, 1, 90000);/* we set the current DTS to 0 so that formats without any timestamps* but durations get some timestamps, formats with some unknown* timestamps have their first few packets buffered and the* timestamps corrected before they are returned to the user */sti-cur_dts RELATIVE_TS_BASE;} else {sti-cur_dts AV_NOPTS_VALUE;}st-index s-nb_streams;st-start_time AV_NOPTS_VALUE;st-duration AV_NOPTS_VALUE;sti-first_dts AV_NOPTS_VALUE;sti-probe_packets s-max_probe_packets;sti-pts_wrap_reference AV_NOPTS_VALUE;sti-pts_wrap_behavior AV_PTS_WRAP_IGNORE;sti-last_IP_pts AV_NOPTS_VALUE;sti-last_dts_for_order_check AV_NOPTS_VALUE;for (int i 0; i MAX_REORDER_DELAY 1; i)sti-pts_buffer[i] AV_NOPTS_VALUE;st-sample_aspect_ratio (AVRational) { 0, 1 };sti-inject_global_side_data si-inject_global_side_data;sti-need_context_update 1;s-streams[s-nb_streams] st;return st;
fail:ff_free_stream(st);return NULL;
}AVCodecContext *avcodec_alloc_context3(const AVCodec *codec)
{AVCodecContext *avctx av_malloc(sizeof(AVCodecContext));if (!avctx)return NULL;if (init_context_defaults(avctx, codec) 0) {av_free(avctx);return NULL;}return avctx;
}static int init_context_defaults(AVCodecContext *s, const AVCodec *codec)
{const FFCodec *const codec2 ffcodec(codec);int flags0;memset(s, 0, sizeof(AVCodecContext));s-av_class av_codec_context_class;s-codec_type codec ? codec-type : AVMEDIA_TYPE_UNKNOWN;if (codec) {s-codec codec;s-codec_id codec-id;}if(s-codec_type AVMEDIA_TYPE_AUDIO)flags AV_OPT_FLAG_AUDIO_PARAM;else if(s-codec_type AVMEDIA_TYPE_VIDEO)flags AV_OPT_FLAG_VIDEO_PARAM;else if(s-codec_type AVMEDIA_TYPE_SUBTITLE)flags AV_OPT_FLAG_SUBTITLE_PARAM;av_opt_set_defaults2(s, flags, flags);av_channel_layout_uninit(s-ch_layout);s-time_base (AVRational){0,1};s-framerate (AVRational){ 0, 1 };s-pkt_timebase (AVRational){ 0, 1 };s-get_buffer2 avcodec_default_get_buffer2;s-get_format avcodec_default_get_format;s-get_encode_buffer avcodec_default_get_encode_buffer;s-execute avcodec_default_execute;s-execute2 avcodec_default_execute2;s-sample_aspect_ratio (AVRational){0,1};s-ch_layout.order AV_CHANNEL_ORDER_UNSPEC;s-pix_fmt AV_PIX_FMT_NONE;s-sw_pix_fmt AV_PIX_FMT_NONE;s-sample_fmt AV_SAMPLE_FMT_NONE;s-reordered_opaque AV_NOPTS_VALUE;if(codec codec2-priv_data_size){s-priv_data av_mallocz(codec2-priv_data_size);if (!s-priv_data)return AVERROR(ENOMEM);if(codec-priv_class){*(const AVClass**)s-priv_data codec-priv_class;av_opt_set_defaults(s-priv_data);}}if (codec codec2-defaults) {int ret;const FFCodecDefault *d codec2-defaults;while (d-key) {ret av_opt_set(s, d-key, d-value, 0);av_assert0(ret 0);d;}}return 0;
}avcodec_alloc_context3() FFmpeg: Core functions/structures.
AVCodecContext *avcodec_alloc_context3(const AVCodec *codec)
{AVCodecContext *avctx av_malloc(sizeof(AVCodecContext));if (!avctx)return NULL;if (init_context_defaults(avctx, codec) 0) {av_free(avctx);return NULL;}return avctx;
}
av_init_packet()
#if FF_API_INIT_PACKET
void av_init_packet(AVPacket *pkt)
{pkt-pts AV_NOPTS_VALUE;pkt-dts AV_NOPTS_VALUE;pkt-pos -1;pkt-duration 0;pkt-flags 0;pkt-stream_index 0;pkt-buf NULL;pkt-side_data NULL;pkt-side_data_elems 0;pkt-opaque NULL;pkt-opaque_ref NULL;pkt-time_base av_make_q(0, 1);
}
#endifav_new_packet() FFmpeg: AVPacket
int av_new_packet(AVPacket *pkt, int size)
{AVBufferRef *buf NULL;int ret packet_alloc(buf, size);if (ret 0)return ret;get_packet_defaults(pkt);pkt-buf buf;pkt-data buf-data;pkt-size size;return 0;
}static int packet_alloc(AVBufferRef **buf, int size)
{int ret;if (size 0 || size INT_MAX - AV_INPUT_BUFFER_PADDING_SIZE)return AVERROR(EINVAL);ret av_buffer_realloc(buf, size AV_INPUT_BUFFER_PADDING_SIZE);if (ret 0)return ret;memset((*buf)-data size, 0, AV_INPUT_BUFFER_PADDING_SIZE);return 0;
}
static void get_packet_defaults(AVPacket *pkt)
{memset(pkt, 0, sizeof(*pkt));pkt-pts AV_NOPTS_VALUE;pkt-dts AV_NOPTS_VALUE;pkt-pos -1;pkt-time_base av_make_q(0, 1);
}
packet_alloc()中调用av_buffer_realloc()为AVPacket分配内存。然后调用memset()将分配的内存置0。 av_frame_alloc() FFmpeg: AVFrame
AVFrame *av_frame_alloc(void)
{AVFrame *frame av_malloc(sizeof(*frame));if (!frame)return NULL;get_frame_defaults(frame);return frame;
}static void get_frame_defaults(AVFrame *frame)
{memset(frame, 0, sizeof(*frame));frame-pts frame-pkt_dts AV_NOPTS_VALUE;frame-best_effort_timestamp AV_NOPTS_VALUE;frame-pkt_duration 0;frame-pkt_pos -1;frame-pkt_size -1;frame-time_base (AVRational){ 0, 1 };frame-key_frame 1;frame-sample_aspect_ratio (AVRational){ 0, 1 };frame-format -1; /* unknown */frame-extended_data frame-data;frame-color_primaries AVCOL_PRI_UNSPECIFIED;frame-color_trc AVCOL_TRC_UNSPECIFIED;frame-colorspace AVCOL_SPC_UNSPECIFIED;frame-color_range AVCOL_RANGE_UNSPECIFIED;frame-chroma_location AVCHROMA_LOC_UNSPECIFIED;frame-flags 0;
}
从av_frame_alloc()的代码可以看出该函数并没有为AVFrame的像素数据分配空间。因此AVFrame中的像素数据需要自行分配空间例如使用av_image_fill_arrays()等函数。avpicture_fill() 弃用av_image_fill_arrays() FFmpeg: Image related
int av_image_fill_arrays(uint8_t *dst_data[4], int dst_linesize[4],const uint8_t *src, enum AVPixelFormat pix_fmt,int width, int height, int align)
{int ret, i;ret av_image_check_size(width, height, 0, NULL);if (ret 0)return ret;ret av_image_fill_linesizes(dst_linesize, pix_fmt, width);if (ret 0)return ret;for (i 0; i 4; i)dst_linesize[i] FFALIGN(dst_linesize[i], align);return av_image_fill_pointers(dst_data, pix_fmt, height, (uint8_t *)src, dst_linesize);
}
av_image_fill_arrays()函数中包含3个函数av_image_check_size()av_image_fill_linesizes()av_image_fill_pointers()。av_image_check_size()用于检查输入的宽高参数是否合理即不能太大或者为负数。
int av_image_check_size(unsigned int w, unsigned int h, int log_offset, void *log_ctx)
{return av_image_check_size2(w, h, INT64_MAX, AV_PIX_FMT_NONE, log_offset, log_ctx);
}
int av_image_check_size2(unsigned int w, unsigned int h, int64_t max_pixels, enum AVPixelFormat pix_fmt, int log_offset, void *log_ctx)
{ImgUtils imgutils {.class imgutils_class,.log_offset log_offset,.log_ctx log_ctx,};int64_t stride av_image_get_linesize(pix_fmt, w, 0);if (stride 0)stride 8LL*w;stride 128*8;if ((int)w0 || (int)h0 || stride INT_MAX || stride*(uint64_t)(h128) INT_MAX) {av_log(imgutils, AV_LOG_ERROR, Picture size %ux%u is invalid\n, w, h);return AVERROR(EINVAL);}if (max_pixels INT64_MAX) {if (w*(int64_t)h max_pixels) {av_log(imgutils, AV_LOG_ERROR,Picture size %ux%u exceeds specified max pixel count %PRId64, see the documentation if you wish to increase it\n,w, h, max_pixels);return AVERROR(EINVAL);}}return 0;
}
av_image_fill_linesizes()用于填充dst_linesize。
int av_image_fill_linesizes(int linesizes[4], enum AVPixelFormat pix_fmt, int width)
{int i, ret;const AVPixFmtDescriptor *desc av_pix_fmt_desc_get(pix_fmt);int max_step [4]; /* max pixel step for each plane */int max_step_comp[4]; /* the component for each plane which has the max pixel step */memset(linesizes, 0, 4*sizeof(linesizes[0]));if (!desc || desc-flags AV_PIX_FMT_FLAG_HWACCEL)return AVERROR(EINVAL);av_image_fill_max_pixsteps(max_step, max_step_comp, desc);for (i 0; i 4; i) {if ((ret image_get_linesize(width, i, max_step[i], max_step_comp[i], desc)) 0)return ret;linesizes[i] ret;}return 0;
}av_image_fill_pointers()则用于填充dst_data。
int av_image_fill_pointers(uint8_t *data[4], enum AVPixelFormat pix_fmt, int height,uint8_t *ptr, const int linesizes[4])
{int i, ret;ptrdiff_t linesizes1[4];size_t sizes[4];memset(data , 0, sizeof(data[0])*4);for (i 0; i 4; i)linesizes1[i] linesizes[i];ret av_image_fill_plane_sizes(sizes, pix_fmt, height, linesizes1);if (ret 0)return ret;ret 0;for (i 0; i 4; i) {if (sizes[i] INT_MAX - ret)return AVERROR(EINVAL);ret sizes[i];}if (!ptr)return ret;data[0] ptr;for (i 1; i 4 sizes[i]; i)data[i] data[i - 1] sizes[i - 1];return ret;
}销毁
avformat_free_context() FFmpeg: Core functionsavformat_free_context调用了各式各样的销毁函数av_opt_free() av_freep() av_dict_free()等这些函数用于释放不同种类的变量
void avformat_free_context(AVFormatContext *s)
{FFFormatContext *si;if (!s)return;si ffformatcontext(s);if (s-oformat s-oformat-deinit si-initialized)s-oformat-deinit(s);av_opt_free(s);if (s-iformat s-iformat-priv_class s-priv_data)av_opt_free(s-priv_data);if (s-oformat s-oformat-priv_class s-priv_data)av_opt_free(s-priv_data);for (unsigned i 0; i s-nb_streams; i)ff_free_stream(s-streams[i]);s-nb_streams 0;for (unsigned i 0; i s-nb_programs; i) {av_dict_free(s-programs[i]-metadata);av_freep(s-programs[i]-stream_index);av_freep(s-programs[i]);}s-nb_programs 0;av_freep(s-programs);av_freep(s-priv_data);while (s-nb_chapters--) {av_dict_free(s-chapters[s-nb_chapters]-metadata);av_freep(s-chapters[s-nb_chapters]);}av_freep(s-chapters);av_dict_free(s-metadata);av_dict_free(si-id3v2_meta);av_packet_free(si-pkt);av_packet_free(si-parse_pkt);av_freep(s-streams);ff_flush_packet_queue(s);av_freep(s-url);av_free(s);
}此处查看释放AVStream的函数ff_free_stream()其与AVFormatContest类似也是调用av_opt_free() av_freep() av_dict_free()等函数用于释放不同种类的变量
void ff_free_stream(AVStream **pst)
{AVStream *st *pst;FFStream *const sti ffstream(st);if (!st)return;for (int i 0; i st-nb_side_data; i)av_freep(st-side_data[i].data);av_freep(st-side_data);if (st-attached_pic.data)av_packet_unref(st-attached_pic);av_parser_close(sti-parser);avcodec_free_context(sti-avctx);av_bsf_free(sti-bsfc);av_freep(sti-priv_pts);av_freep(sti-index_entries);av_freep(sti-probe_data.buf);av_bsf_free(sti-extract_extradata.bsf);if (sti-info) {av_freep(sti-info-duration_error);av_freep(sti-info);}av_dict_free(st-metadata);avcodec_parameters_free(st-codecpar);av_freep(st-priv_data);av_freep(pst);
}如果使用了parser会调用av_parser_close()关闭parser
void av_parser_close(AVCodecParserContext *s)
{if (s) {if (s-parser-parser_close)s-parser-parser_close(s);av_freep(s-priv_data);av_free(s);}
}avio_context_free() FFmpeg: libavformat/avio.h File Referenceavcodec_free_context() FFmpeg: Core functions/structures.av_frame_free() FFmpeg: AVFrame
void av_frame_free(AVFrame **frame)
{if (!frame || !*frame)return;av_frame_unref(*frame);av_freep(frame);
}在释放AVFrame结构体之前首先调用了一个函数av_frame_unref()。av_frame_unref()也是一个FFmpeg的API它的作用是释放AVFrame中参考的缓存还没完全弄懂并且重置AVFrame中的字段。调用这个函数的目的应该是为了确保AVFrame可以被正常释放。代码如下
void av_frame_unref(AVFrame *frame)
{int i;if (!frame)return;wipe_side_data(frame);for (i 0; i FF_ARRAY_ELEMS(frame-buf); i)av_buffer_unref(frame-buf[i]);for (i 0; i frame-nb_extended_buf; i)av_buffer_unref(frame-extended_buf[i]);av_freep(frame-extended_buf);av_dict_free(frame-metadata);av_buffer_unref(frame-hw_frames_ctx);av_buffer_unref(frame-opaque_ref);av_buffer_unref(frame-private_ref);if (frame-extended_data ! frame-data)av_freep(frame-extended_data);av_channel_layout_uninit(frame-ch_layout);get_frame_defaults(frame);
}
av_packet_free()从代码可以看出av_packet_free()调用av_packet_unref()释放AVPacket中的数据调用了av_packet_free_side_data()释放了side_data存储封装格式可以提供的额外的数据。
void av_packet_free(AVPacket **pkt)
{if (!pkt || !*pkt)return;av_packet_unref(*pkt);av_freep(pkt);
}void av_packet_unref(AVPacket *pkt)
{av_packet_free_side_data(pkt);av_buffer_unref(pkt-opaque_ref);av_buffer_unref(pkt-buf);get_packet_defaults(pkt);
} 请使用手机扫一扫x
