驻马店做网站推广,WordPress京东自动转链插件,哪里可以学网站建设,徐州市城乡建设局门户网站libavformat#xff08;lavf#xff09;是一个用于处理各种媒体容器格式的库。它的主要两个目的是去复用#xff08;即将媒体文件拆分为组件流#xff09;和复用的反向过程#xff08;以指定的容器格式写入提供的数据#xff09;。它还有一个I/O模块#xff0c;支持多种…libavformatlavf是一个用于处理各种媒体容器格式的库。它的主要两个目的是去复用即将媒体文件拆分为组件流和复用的反向过程以指定的容器格式写入提供的数据。它还有一个I/O模块支持多种访问数据的协议如文件、tcp、http等。在使用lavf之前您需要调用av_register_all来注册所有已编译的复用器、解复用器和协议。除非您绝对确定不会使用libavformat的网络功能否则还应该调用avformat_network_init
一、媒体流封装Muxing
媒体流封装主要是指以AVPackets的形式获取编码后的数据后以指定的容器格式将其写入到文件或者其他方式输出到字节流中。
Muxing实际执行的主要API有
初始化avformat_alloc_output_context2();
创建媒体流如果有的话avformat_new_stream()
写文件头avformat_write_header()
写数据包av_write_frame()/av_interleaved_write_frame();
写文件尾av_write_trailer();
流程图 代码示例
在官方源码/doc/examples/muxing.c
#include stdlib.h
#include stdio.h
#include string.h
#include math.h#include libavutil/avassert.h
#include libavutil/channel_layout.h
#include libavutil/opt.h
#include libavutil/mathematics.h
#include libavutil/timestamp.h
#include libavcodec/avcodec.h
#include libavformat/avformat.h
#include libswscale/swscale.h
#include libswresample/swresample.h#define STREAM_DURATION 10.0
#define STREAM_FRAME_RATE 25 /* 25 images/s */
#define STREAM_PIX_FMT AV_PIX_FMT_YUV420P /* default pix_fmt */#define SCALE_FLAGS SWS_BICUBIC// a wrapper around a single output AVStream
typedef struct OutputStream {AVStream *st;AVCodecContext *enc;/* pts of the next frame that will be generated */int64_t next_pts;int samples_count;AVFrame *frame;AVFrame *tmp_frame;AVPacket *tmp_pkt;float t, tincr, tincr2;struct SwsContext *sws_ctx;struct SwrContext *swr_ctx;
} OutputStream;static void log_packet(const AVFormatContext *fmt_ctx, const AVPacket *pkt)
{AVRational *time_base fmt_ctx-streams[pkt-stream_index]-time_base;printf(pts:%s pts_time:%s dts:%s dts_time:%s duration:%s duration_time:%s stream_index:%d\n,av_ts2str(pkt-pts), av_ts2timestr(pkt-pts, time_base),av_ts2str(pkt-dts), av_ts2timestr(pkt-dts, time_base),av_ts2str(pkt-duration), av_ts2timestr(pkt-duration, time_base),pkt-stream_index);
}static int write_frame(AVFormatContext *fmt_ctx, AVCodecContext *c,AVStream *st, AVFrame *frame, AVPacket *pkt)
{int ret;// send the frame to the encoderret avcodec_send_frame(c, frame);if (ret 0) {fprintf(stderr, Error sending a frame to the encoder: %s\n,av_err2str(ret));exit(1);}while (ret 0) {ret avcodec_receive_packet(c, pkt);if (ret AVERROR(EAGAIN) || ret AVERROR_EOF)break;else if (ret 0) {fprintf(stderr, Error encoding a frame: %s\n, av_err2str(ret));exit(1);}/* rescale output packet timestamp values from codec to stream timebase */av_packet_rescale_ts(pkt, c-time_base, st-time_base);pkt-stream_index st-index;/* Write the compressed frame to the media file. */log_packet(fmt_ctx, pkt);ret av_interleaved_write_frame(fmt_ctx, pkt);/* pkt is now blank (av_interleaved_write_frame() takes ownership of* its contents and resets pkt), so that no unreferencing is necessary.* This would be different if one used av_write_frame(). */if (ret 0) {fprintf(stderr, Error while writing output packet: %s\n, av_err2str(ret));exit(1);}}return ret AVERROR_EOF ? 1 : 0;
}/* Add an output stream. */
static void add_stream(OutputStream *ost, AVFormatContext *oc,const AVCodec **codec,enum AVCodecID codec_id)
{AVCodecContext *c;int i;/* find the encoder */*codec avcodec_find_encoder(codec_id);if (!(*codec)) {fprintf(stderr, Could not find encoder for %s\n,avcodec_get_name(codec_id));exit(1);}ost-tmp_pkt av_packet_alloc();if (!ost-tmp_pkt) {fprintf(stderr, Could not allocate AVPacket\n);exit(1);}ost-st avformat_new_stream(oc, NULL);if (!ost-st) {fprintf(stderr, Could not allocate stream\n);exit(1);}ost-st-id oc-nb_streams-1;c avcodec_alloc_context3(*codec);if (!c) {fprintf(stderr, Could not alloc an encoding context\n);exit(1);}ost-enc c;switch ((*codec)-type) {case AVMEDIA_TYPE_AUDIO:c-sample_fmt (*codec)-sample_fmts ?(*codec)-sample_fmts[0] : AV_SAMPLE_FMT_FLTP;c-bit_rate 64000;c-sample_rate 44100;if ((*codec)-supported_samplerates) {c-sample_rate (*codec)-supported_samplerates[0];for (i 0; (*codec)-supported_samplerates[i]; i) {if ((*codec)-supported_samplerates[i] 44100)c-sample_rate 44100;}}c-channels av_get_channel_layout_nb_channels(c-channel_layout);c-channel_layout AV_CH_LAYOUT_STEREO;if ((*codec)-channel_layouts) {c-channel_layout (*codec)-channel_layouts[0];for (i 0; (*codec)-channel_layouts[i]; i) {if ((*codec)-channel_layouts[i] AV_CH_LAYOUT_STEREO)c-channel_layout AV_CH_LAYOUT_STEREO;}}c-channels av_get_channel_layout_nb_channels(c-channel_layout);ost-st-time_base (AVRational){ 1, c-sample_rate };break;case AVMEDIA_TYPE_VIDEO:c-codec_id codec_id;c-bit_rate 400000;/* Resolution must be a multiple of two. */c-width 352;c-height 288;/* timebase: This is the fundamental unit of time (in seconds) in terms* of which frame timestamps are represented. For fixed-fps content,* timebase should be 1/framerate and timestamp increments should be* identical to 1. */ost-st-time_base (AVRational){ 1, STREAM_FRAME_RATE };c-time_base ost-st-time_base;c-gop_size 12; /* emit one intra frame every twelve frames at most */c-pix_fmt STREAM_PIX_FMT;if (c-codec_id AV_CODEC_ID_MPEG2VIDEO) {/* just for testing, we also add B-frames */c-max_b_frames 2;}if (c-codec_id AV_CODEC_ID_MPEG1VIDEO) {/* Needed to avoid using macroblocks in which some coeffs overflow.* This does not happen with normal video, it just happens here as* the motion of the chroma plane does not match the luma plane. */c-mb_decision 2;}break;default:break;}/* Some formats want stream headers to be separate. */if (oc-oformat-flags AVFMT_GLOBALHEADER)c-flags | AV_CODEC_FLAG_GLOBAL_HEADER;
}/**************************************************************/
/* audio output */static AVFrame *alloc_audio_frame(enum AVSampleFormat sample_fmt,uint64_t channel_layout,int sample_rate, int nb_samples)
{AVFrame *frame av_frame_alloc();int ret;if (!frame) {fprintf(stderr, Error allocating an audio frame\n);exit(1);}frame-format sample_fmt;frame-channel_layout channel_layout;frame-sample_rate sample_rate;frame-nb_samples nb_samples;if (nb_samples) {ret av_frame_get_buffer(frame, 0);if (ret 0) {fprintf(stderr, Error allocating an audio buffer\n);exit(1);}}return frame;
}static void open_audio(AVFormatContext *oc, const AVCodec *codec,OutputStream *ost, AVDictionary *opt_arg)
{AVCodecContext *c;int nb_samples;int ret;AVDictionary *opt NULL;c ost-enc;/* open it */av_dict_copy(opt, opt_arg, 0);ret avcodec_open2(c, codec, opt);av_dict_free(opt);if (ret 0) {fprintf(stderr, Could not open audio codec: %s\n, av_err2str(ret));exit(1);}/* init signal generator */ost-t 0;ost-tincr 2 * M_PI * 110.0 / c-sample_rate;/* increment frequency by 110 Hz per second */ost-tincr2 2 * M_PI * 110.0 / c-sample_rate / c-sample_rate;if (c-codec-capabilities AV_CODEC_CAP_VARIABLE_FRAME_SIZE)nb_samples 10000;elsenb_samples c-frame_size;ost-frame alloc_audio_frame(c-sample_fmt, c-channel_layout,c-sample_rate, nb_samples);ost-tmp_frame alloc_audio_frame(AV_SAMPLE_FMT_S16, c-channel_layout,c-sample_rate, nb_samples);/* copy the stream parameters to the muxer */ret avcodec_parameters_from_context(ost-st-codecpar, c);if (ret 0) {fprintf(stderr, Could not copy the stream parameters\n);exit(1);}/* create resampler context */ost-swr_ctx swr_alloc();if (!ost-swr_ctx) {fprintf(stderr, Could not allocate resampler context\n);exit(1);}/* set options */av_opt_set_int (ost-swr_ctx, in_channel_count, c-channels, 0);av_opt_set_int (ost-swr_ctx, in_sample_rate, c-sample_rate, 0);av_opt_set_sample_fmt(ost-swr_ctx, in_sample_fmt, AV_SAMPLE_FMT_S16, 0);av_opt_set_int (ost-swr_ctx, out_channel_count, c-channels, 0);av_opt_set_int (ost-swr_ctx, out_sample_rate, c-sample_rate, 0);av_opt_set_sample_fmt(ost-swr_ctx, out_sample_fmt, c-sample_fmt, 0);/* initialize the resampling context */if ((ret swr_init(ost-swr_ctx)) 0) {fprintf(stderr, Failed to initialize the resampling context\n);exit(1);}
}/* Prepare a 16 bit dummy audio frame of frame_size samples and* nb_channels channels. */
static AVFrame *get_audio_frame(OutputStream *ost)
{AVFrame *frame ost-tmp_frame;int j, i, v;int16_t *q (int16_t*)frame-data[0];/* check if we want to generate more frames */if (av_compare_ts(ost-next_pts, ost-enc-time_base,STREAM_DURATION, (AVRational){ 1, 1 }) 0)return NULL;for (j 0; j frame-nb_samples; j) {v (int)(sin(ost-t) * 10000);for (i 0; i ost-enc-channels; i)*q v;ost-t ost-tincr;ost-tincr ost-tincr2;}frame-pts ost-next_pts;ost-next_pts frame-nb_samples;return frame;
}/** encode one audio frame and send it to the muxer* return 1 when encoding is finished, 0 otherwise*/
static int write_audio_frame(AVFormatContext *oc, OutputStream *ost)
{AVCodecContext *c;AVFrame *frame;int ret;int dst_nb_samples;c ost-enc;frame get_audio_frame(ost);if (frame) {/* convert samples from native format to destination codec format, using the resampler *//* compute destination number of samples */dst_nb_samples av_rescale_rnd(swr_get_delay(ost-swr_ctx, c-sample_rate) frame-nb_samples,c-sample_rate, c-sample_rate, AV_ROUND_UP);av_assert0(dst_nb_samples frame-nb_samples);/* when we pass a frame to the encoder, it may keep a reference to it* internally;* make sure we do not overwrite it here*/ret av_frame_make_writable(ost-frame);if (ret 0)exit(1);/* convert to destination format */ret swr_convert(ost-swr_ctx,ost-frame-data, dst_nb_samples,(const uint8_t **)frame-data, frame-nb_samples);if (ret 0) {fprintf(stderr, Error while converting\n);exit(1);}frame ost-frame;frame-pts av_rescale_q(ost-samples_count, (AVRational){1, c-sample_rate}, c-time_base);ost-samples_count dst_nb_samples;}return write_frame(oc, c, ost-st, frame, ost-tmp_pkt);
}/**************************************************************/
/* video output */static AVFrame *alloc_picture(enum AVPixelFormat pix_fmt, int width, int height)
{AVFrame *picture;int ret;picture av_frame_alloc();if (!picture)return NULL;picture-format pix_fmt;picture-width width;picture-height height;/* allocate the buffers for the frame data */ret av_frame_get_buffer(picture, 0);if (ret 0) {fprintf(stderr, Could not allocate frame data.\n);exit(1);}return picture;
}static void open_video(AVFormatContext *oc, const AVCodec *codec,OutputStream *ost, AVDictionary *opt_arg)
{int ret;AVCodecContext *c ost-enc;AVDictionary *opt NULL;av_dict_copy(opt, opt_arg, 0);/* open the codec */ret avcodec_open2(c, codec, opt);av_dict_free(opt);if (ret 0) {fprintf(stderr, Could not open video codec: %s\n, av_err2str(ret));exit(1);}/* allocate and init a re-usable frame */ost-frame alloc_picture(c-pix_fmt, c-width, c-height);if (!ost-frame) {fprintf(stderr, Could not allocate video frame\n);exit(1);}/* If the output format is not YUV420P, then a temporary YUV420P* picture is needed too. It is then converted to the required* output format. */ost-tmp_frame NULL;if (c-pix_fmt ! AV_PIX_FMT_YUV420P) {ost-tmp_frame alloc_picture(AV_PIX_FMT_YUV420P, c-width, c-height);if (!ost-tmp_frame) {fprintf(stderr, Could not allocate temporary picture\n);exit(1);}}/* copy the stream parameters to the muxer */ret avcodec_parameters_from_context(ost-st-codecpar, c);if (ret 0) {fprintf(stderr, Could not copy the stream parameters\n);exit(1);}
}/* Prepare a dummy image. */
static void fill_yuv_image(AVFrame *pict, int frame_index,int width, int height)
{int x, y, i;i frame_index;/* Y */for (y 0; y height; y)for (x 0; x width; x)pict-data[0][y * pict-linesize[0] x] x y i * 3;/* Cb and Cr */for (y 0; y height / 2; y) {for (x 0; x width / 2; x) {pict-data[1][y * pict-linesize[1] x] 128 y i * 2;pict-data[2][y * pict-linesize[2] x] 64 x i * 5;}}
}static AVFrame *get_video_frame(OutputStream *ost)
{AVCodecContext *c ost-enc;/* check if we want to generate more frames */if (av_compare_ts(ost-next_pts, c-time_base,STREAM_DURATION, (AVRational){ 1, 1 }) 0)return NULL;/* when we pass a frame to the encoder, it may keep a reference to it* internally; make sure we do not overwrite it here */if (av_frame_make_writable(ost-frame) 0)exit(1);if (c-pix_fmt ! AV_PIX_FMT_YUV420P) {/* as we only generate a YUV420P picture, we must convert it* to the codec pixel format if needed */if (!ost-sws_ctx) {ost-sws_ctx sws_getContext(c-width, c-height,AV_PIX_FMT_YUV420P,c-width, c-height,c-pix_fmt,SCALE_FLAGS, NULL, NULL, NULL);if (!ost-sws_ctx) {fprintf(stderr,Could not initialize the conversion context\n);exit(1);}}fill_yuv_image(ost-tmp_frame, ost-next_pts, c-width, c-height);sws_scale(ost-sws_ctx, (const uint8_t * const *) ost-tmp_frame-data,ost-tmp_frame-linesize, 0, c-height, ost-frame-data,ost-frame-linesize);} else {fill_yuv_image(ost-frame, ost-next_pts, c-width, c-height);}ost-frame-pts ost-next_pts;return ost-frame;
}/** encode one video frame and send it to the muxer* return 1 when encoding is finished, 0 otherwise*/
static int write_video_frame(AVFormatContext *oc, OutputStream *ost)
{return write_frame(oc, ost-enc, ost-st, get_video_frame(ost), ost-tmp_pkt);
}static void close_stream(AVFormatContext *oc, OutputStream *ost)
{avcodec_free_context(ost-enc);av_frame_free(ost-frame);av_frame_free(ost-tmp_frame);av_packet_free(ost-tmp_pkt);sws_freeContext(ost-sws_ctx);swr_free(ost-swr_ctx);
}/**************************************************************/
/* media file output */int main(int argc, char **argv)
{OutputStream video_st { 0 }, audio_st { 0 };const AVOutputFormat *fmt;const char *filename;AVFormatContext *oc;const AVCodec *audio_codec, *video_codec;int ret;int have_video 0, have_audio 0;int encode_video 0, encode_audio 0;AVDictionary *opt NULL;int i;if (argc 2) {printf(usage: %s output_file\nAPI example program to output a media file with libavformat.\nThis program generates a synthetic audio and video stream, encodes and\nmuxes them into a file named output_file.\nThe output format is automatically guessed according to the file extension.\nRaw images can also be output by using %%d in the filename.\n\n, argv[0]);return 1;}filename argv[1];for (i 2; i1 argc; i2) {if (!strcmp(argv[i], -flags) || !strcmp(argv[i], -fflags))av_dict_set(opt, argv[i]1, argv[i1], 0);}/* allocate the output media context */avformat_alloc_output_context2(oc, NULL, NULL, filename);if (!oc) {printf(Could not deduce output format from file extension: using MPEG.\n);avformat_alloc_output_context2(oc, NULL, mpeg, filename);}if (!oc)return 1;fmt oc-oformat;/* Add the audio and video streams using the default format codecs* and initialize the codecs. */if (fmt-video_codec ! AV_CODEC_ID_NONE) {add_stream(video_st, oc, video_codec, fmt-video_codec);have_video 1;encode_video 1;}if (fmt-audio_codec ! AV_CODEC_ID_NONE) {add_stream(audio_st, oc, audio_codec, fmt-audio_codec);have_audio 1;encode_audio 1;}/* Now that all the parameters are set, we can open the audio and* video codecs and allocate the necessary encode buffers. */if (have_video)open_video(oc, video_codec, video_st, opt);if (have_audio)open_audio(oc, audio_codec, audio_st, opt);av_dump_format(oc, 0, filename, 1);/* open the output file, if needed */if (!(fmt-flags AVFMT_NOFILE)) {ret avio_open(oc-pb, filename, AVIO_FLAG_WRITE);if (ret 0) {fprintf(stderr, Could not open %s: %s\n, filename,av_err2str(ret));return 1;}}/* Write the stream header, if any. */ret avformat_write_header(oc, opt);if (ret 0) {fprintf(stderr, Error occurred when opening output file: %s\n,av_err2str(ret));return 1;}while (encode_video || encode_audio) {/* select the stream to encode */if (encode_video (!encode_audio || av_compare_ts(video_st.next_pts, video_st.enc-time_base,audio_st.next_pts, audio_st.enc-time_base) 0)) {encode_video !write_video_frame(oc, video_st);} else {encode_audio !write_audio_frame(oc, audio_st);}}/* Write the trailer, if any. The trailer must be written before you* close the CodecContexts open when you wrote the header; otherwise* av_write_trailer() may try to use memory that was freed on* av_codec_close(). */av_write_trailer(oc);/* Close each codec. */if (have_video)close_stream(oc, video_st);if (have_audio)close_stream(oc, audio_st);if (!(fmt-flags AVFMT_NOFILE))/* Close the output file. */avio_closep(oc-pb);/* free the stream */avformat_free_context(oc);return 0;
}
