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FFmpeg 是一个可以处理音视频的软件#xff0c;功能非常强大#xff0c;主要包括#xff0c;编解码转换#xff0c;封装格式转换#xff0c;滤镜特效。FFmpeg支持各种网络协议#xff0c;支持 RTMP #xff0c;RTSP#xff0c;HLS 等高层协议的推拉流#xff0c…介绍
FFmpeg 是一个可以处理音视频的软件功能非常强大主要包括编解码转换封装格式转换滤镜特效。FFmpeg支持各种网络协议支持 RTMP RTSPHLS 等高层协议的推拉流也支持更底层的TCP/UDP 协议推拉流。FFmpeg 可以在 WindowsLinuxMaciOSAndroid等操作系统上运行。FFmpeg 是 Fast Forward mpeg 的缩写FFMPEG从功能上划分为几个模块分别为核心工具libutils、媒体格式libavformat、编解码libavcodec、设备libavdevice和后处理libavfilter, libswscale, libpostproc分别负责提供公用的功能函数、实现多媒体文件的读包和写包、完成音视频的编解码、管理音视频设备的操作以及进行音视频后处理。ffmpeg的可执行文件是 FFmpeg 官方提供的转换工具是命令行工具核心代码主要在 ffmpeg.c文件中。
ffmpeg.c函数关系分析总图 关键函数介绍
transcode()
转换的核心功能主要就在 transcode()函数中此函数中最核心的就是 transcode_step()该函数完成了音视频的转换的核心能力。其中 transcode_init()主要完成一些初始化的工作内部通过init_input_stream()来实现调用 API函数avcodec_open2()完成解码器的打开工作。
transcode_step()
transcode_step()是完成音视频转码的核心函数其中 process_input()完成解码功能模块reap_filter()完成了编码功能模块。
process_input()
process_input()函数实现了解码功能其中 process_input_packet()是完成解码的核心函数。 在 process_input_packet()中会根据不同的音视频解码需要调用不同的函数音频调用的就是 decode_audio()视频调用的是 decode_video()函数字幕调用的是 transcode_subtitles()函数如果只是进行 copy 功能需要调用 do_streamcopy()函数。 在decode_video()函数中主要完成了解码和发送 frame 的功能其中 decode()中调用了 API 函数avcodec_send_packet()、avcodec_receive_frame()两个函数完成音视频多媒体的解码功能模块send_frame_to_filters()主要是对解码后的帧等送到滤镜中便于下一步的编码使用。
reap_filter()
reap_filter()函数实现了编码功能。其中视频编码的核心函数是do_video_out()函数音频编码的核心函数是 do_audio_out()函数。 其中 do_video_out()函数完成是视频的 frame 到 packet 的过程即编码功能。其中调用了 API 函数avcodec_send_frame()、avcodec_receive_packet()完成编码。而 output_packet()完成了将最后的视频包 packet 输出的功能。
官方转码实例
该 example 主要根据新版 API 完成了音视频转码的功能。
/** Copyright (c) 2010 Nicolas George* Copyright (c) 2011 Stefano Sabatini* Copyright (c) 2014 Andrey Utkin** Permission is hereby granted, free of charge, to any person obtaining a copy* of this software and associated documentation files (the Software), to deal* in the Software without restriction, including without limitation the rights* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell* copies of the Software, and to permit persons to whom the Software is* furnished to do so, subject to the following conditions:** The above copyright notice and this permission notice shall be included in* all copies or substantial portions of the Software.** THE SOFTWARE IS PROVIDED AS IS, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN* THE SOFTWARE.*//*** file* API example for demuxing, decoding, filtering, encoding and muxing* example transcoding.c*/#include libavcodec/avcodec.h
#include libavformat/avformat.h
#include libavfilter/buffersink.h
#include libavfilter/buffersrc.h
#include libavutil/opt.h
#include libavutil/pixdesc.hstatic AVFormatContext *ifmt_ctx;
static AVFormatContext *ofmt_ctx;
typedef struct FilteringContext {AVFilterContext *buffersink_ctx;AVFilterContext *buffersrc_ctx;AVFilterGraph *filter_graph;
} FilteringContext;
static FilteringContext *filter_ctx;typedef struct StreamContext {AVCodecContext *dec_ctx;AVCodecContext *enc_ctx;
} StreamContext;
static StreamContext *stream_ctx;static int open_input_file(const char *filename)
{int ret;unsigned int i;ifmt_ctx NULL;if ((ret avformat_open_input(ifmt_ctx, filename, NULL, NULL)) 0) {av_log(NULL, AV_LOG_ERROR, Cannot open input file\n);return ret;}if ((ret avformat_find_stream_info(ifmt_ctx, NULL)) 0) {av_log(NULL, AV_LOG_ERROR, Cannot find stream information\n);return ret;}stream_ctx av_mallocz_array(ifmt_ctx-nb_streams, sizeof(*stream_ctx));if (!stream_ctx)return AVERROR(ENOMEM);for (i 0; i ifmt_ctx-nb_streams; i) {AVStream *stream ifmt_ctx-streams[i];AVCodec *dec avcodec_find_decoder(stream-codecpar-codec_id);AVCodecContext *codec_ctx;if (!dec) {av_log(NULL, AV_LOG_ERROR, Failed to find decoder for stream #%u\n, i);return AVERROR_DECODER_NOT_FOUND;}codec_ctx avcodec_alloc_context3(dec);if (!codec_ctx) {av_log(NULL, AV_LOG_ERROR, Failed to allocate the decoder context for stream #%u\n, i);return AVERROR(ENOMEM);}ret avcodec_parameters_to_context(codec_ctx, stream-codecpar);if (ret 0) {av_log(NULL, AV_LOG_ERROR, Failed to copy decoder parameters to input decoder context for stream #%u\n, i);return ret;}/* Reencode video audio and remux subtitles etc. */if (codec_ctx-codec_type AVMEDIA_TYPE_VIDEO|| codec_ctx-codec_type AVMEDIA_TYPE_AUDIO) {if (codec_ctx-codec_type AVMEDIA_TYPE_VIDEO)codec_ctx-framerate av_guess_frame_rate(ifmt_ctx, stream, NULL);/* Open decoder */ret avcodec_open2(codec_ctx, dec, NULL);if (ret 0) {av_log(NULL, AV_LOG_ERROR, Failed to open decoder for stream #%u\n, i);return ret;}}stream_ctx[i].dec_ctx codec_ctx;}av_dump_format(ifmt_ctx, 0, filename, 0);return 0;
}static int open_output_file(const char *filename)
{AVStream *out_stream;AVStream *in_stream;AVCodecContext *dec_ctx, *enc_ctx;AVCodec *encoder;int ret;unsigned int i;ofmt_ctx NULL;avformat_alloc_output_context2(ofmt_ctx, NULL, NULL, filename);if (!ofmt_ctx) {av_log(NULL, AV_LOG_ERROR, Could not create output context\n);return AVERROR_UNKNOWN;}for (i 0; i ifmt_ctx-nb_streams; i) {out_stream avformat_new_stream(ofmt_ctx, NULL);if (!out_stream) {av_log(NULL, AV_LOG_ERROR, Failed allocating output stream\n);return AVERROR_UNKNOWN;}in_stream ifmt_ctx-streams[i];dec_ctx stream_ctx[i].dec_ctx;if (dec_ctx-codec_type AVMEDIA_TYPE_VIDEO|| dec_ctx-codec_type AVMEDIA_TYPE_AUDIO) {/* in this example, we choose transcoding to same codec */encoder avcodec_find_encoder(dec_ctx-codec_id);if (!encoder) {av_log(NULL, AV_LOG_FATAL, Necessary encoder not found\n);return AVERROR_INVALIDDATA;}enc_ctx avcodec_alloc_context3(encoder);if (!enc_ctx) {av_log(NULL, AV_LOG_FATAL, Failed to allocate the encoder context\n);return AVERROR(ENOMEM);}/* In this example, we transcode to same properties (picture size,* sample rate etc.). These properties can be changed for output* streams easily using filters */if (dec_ctx-codec_type AVMEDIA_TYPE_VIDEO) {enc_ctx-height dec_ctx-height;enc_ctx-width dec_ctx-width;enc_ctx-sample_aspect_ratio dec_ctx-sample_aspect_ratio;/* take first format from list of supported formats */if (encoder-pix_fmts)enc_ctx-pix_fmt encoder-pix_fmts[0];elseenc_ctx-pix_fmt dec_ctx-pix_fmt;/* video time_base can be set to whatever is handy and supported by encoder */enc_ctx-time_base av_inv_q(dec_ctx-framerate);} else {enc_ctx-sample_rate dec_ctx-sample_rate;enc_ctx-channel_layout dec_ctx-channel_layout;enc_ctx-channels av_get_channel_layout_nb_channels(enc_ctx-channel_layout);/* take first format from list of supported formats */enc_ctx-sample_fmt encoder-sample_fmts[0];enc_ctx-time_base (AVRational){1, enc_ctx-sample_rate};}if (ofmt_ctx-oformat-flags AVFMT_GLOBALHEADER)enc_ctx-flags | AV_CODEC_FLAG_GLOBAL_HEADER;/* Third parameter can be used to pass settings to encoder */ret avcodec_open2(enc_ctx, encoder, NULL);if (ret 0) {av_log(NULL, AV_LOG_ERROR, Cannot open video encoder for stream #%u\n, i);return ret;}ret avcodec_parameters_from_context(out_stream-codecpar, enc_ctx);if (ret 0) {av_log(NULL, AV_LOG_ERROR, Failed to copy encoder parameters to output stream #%u\n, i);return ret;}out_stream-time_base enc_ctx-time_base;stream_ctx[i].enc_ctx enc_ctx;} else if (dec_ctx-codec_type AVMEDIA_TYPE_UNKNOWN) {av_log(NULL, AV_LOG_FATAL, Elementary stream #%d is of unknown type, cannot proceed\n, i);return AVERROR_INVALIDDATA;} else {/* if this stream must be remuxed */ret avcodec_parameters_copy(out_stream-codecpar, in_stream-codecpar);if (ret 0) {av_log(NULL, AV_LOG_ERROR, Copying parameters for stream #%u failed\n, i);return ret;}out_stream-time_base in_stream-time_base;}}av_dump_format(ofmt_ctx, 0, filename, 1);if (!(ofmt_ctx-oformat-flags AVFMT_NOFILE)) {ret avio_open(ofmt_ctx-pb, filename, AVIO_FLAG_WRITE);if (ret 0) {av_log(NULL, AV_LOG_ERROR, Could not open output file %s, filename);return ret;}}/* init muxer, write output file header */ret avformat_write_header(ofmt_ctx, NULL);if (ret 0) {av_log(NULL, AV_LOG_ERROR, Error occurred when opening output file\n);return ret;}return 0;
}static int init_filter(FilteringContext* fctx, AVCodecContext *dec_ctx,AVCodecContext *enc_ctx, const char *filter_spec)
{char args[512];int ret 0;const AVFilter *buffersrc NULL;const AVFilter *buffersink NULL;AVFilterContext *buffersrc_ctx NULL;AVFilterContext *buffersink_ctx NULL;AVFilterInOut *outputs avfilter_inout_alloc();AVFilterInOut *inputs avfilter_inout_alloc();AVFilterGraph *filter_graph avfilter_graph_alloc();if (!outputs || !inputs || !filter_graph) {ret AVERROR(ENOMEM);goto end;}if (dec_ctx-codec_type AVMEDIA_TYPE_VIDEO) {buffersrc avfilter_get_by_name(buffer);buffersink avfilter_get_by_name(buffersink);if (!buffersrc || !buffersink) {av_log(NULL, AV_LOG_ERROR, filtering source or sink element not found\n);ret AVERROR_UNKNOWN;goto end;}snprintf(args, sizeof(args),video_size%dx%d:pix_fmt%d:time_base%d/%d:pixel_aspect%d/%d,dec_ctx-width, dec_ctx-height, dec_ctx-pix_fmt,dec_ctx-time_base.num, dec_ctx-time_base.den,dec_ctx-sample_aspect_ratio.num,dec_ctx-sample_aspect_ratio.den);ret avfilter_graph_create_filter(buffersrc_ctx, buffersrc, in,args, NULL, filter_graph);if (ret 0) {av_log(NULL, AV_LOG_ERROR, Cannot create buffer source\n);goto end;}ret avfilter_graph_create_filter(buffersink_ctx, buffersink, out,NULL, NULL, filter_graph);if (ret 0) {av_log(NULL, AV_LOG_ERROR, Cannot create buffer sink\n);goto end;}ret av_opt_set_bin(buffersink_ctx, pix_fmts,(uint8_t*)enc_ctx-pix_fmt, sizeof(enc_ctx-pix_fmt),AV_OPT_SEARCH_CHILDREN);if (ret 0) {av_log(NULL, AV_LOG_ERROR, Cannot set output pixel format\n);goto end;}} else if (dec_ctx-codec_type AVMEDIA_TYPE_AUDIO) {buffersrc avfilter_get_by_name(abuffer);buffersink avfilter_get_by_name(abuffersink);if (!buffersrc || !buffersink) {av_log(NULL, AV_LOG_ERROR, filtering source or sink element not found\n);ret AVERROR_UNKNOWN;goto end;}if (!dec_ctx-channel_layout)dec_ctx-channel_layout av_get_default_channel_layout(dec_ctx-channels);snprintf(args, sizeof(args),time_base%d/%d:sample_rate%d:sample_fmt%s:channel_layout0x%PRIx64,dec_ctx-time_base.num, dec_ctx-time_base.den, dec_ctx-sample_rate,av_get_sample_fmt_name(dec_ctx-sample_fmt),dec_ctx-channel_layout);ret avfilter_graph_create_filter(buffersrc_ctx, buffersrc, in,args, NULL, filter_graph);if (ret 0) {av_log(NULL, AV_LOG_ERROR, Cannot create audio buffer source\n);goto end;}ret avfilter_graph_create_filter(buffersink_ctx, buffersink, out,NULL, NULL, filter_graph);if (ret 0) {av_log(NULL, AV_LOG_ERROR, Cannot create audio buffer sink\n);goto end;}ret av_opt_set_bin(buffersink_ctx, sample_fmts,(uint8_t*)enc_ctx-sample_fmt, sizeof(enc_ctx-sample_fmt),AV_OPT_SEARCH_CHILDREN);if (ret 0) {av_log(NULL, AV_LOG_ERROR, Cannot set output sample format\n);goto end;}ret av_opt_set_bin(buffersink_ctx, channel_layouts,(uint8_t*)enc_ctx-channel_layout,sizeof(enc_ctx-channel_layout), AV_OPT_SEARCH_CHILDREN);if (ret 0) {av_log(NULL, AV_LOG_ERROR, Cannot set output channel layout\n);goto end;}ret av_opt_set_bin(buffersink_ctx, sample_rates,(uint8_t*)enc_ctx-sample_rate, sizeof(enc_ctx-sample_rate),AV_OPT_SEARCH_CHILDREN);if (ret 0) {av_log(NULL, AV_LOG_ERROR, Cannot set output sample rate\n);goto end;}} else {ret AVERROR_UNKNOWN;goto end;}/* Endpoints for the filter graph. */outputs-name av_strdup(in);outputs-filter_ctx buffersrc_ctx;outputs-pad_idx 0;outputs-next NULL;inputs-name av_strdup(out);inputs-filter_ctx buffersink_ctx;inputs-pad_idx 0;inputs-next NULL;if (!outputs-name || !inputs-name) {ret AVERROR(ENOMEM);goto end;}if ((ret avfilter_graph_parse_ptr(filter_graph, filter_spec,inputs, outputs, NULL)) 0)goto end;if ((ret avfilter_graph_config(filter_graph, NULL)) 0)goto end;/* Fill FilteringContext */fctx-buffersrc_ctx buffersrc_ctx;fctx-buffersink_ctx buffersink_ctx;fctx-filter_graph filter_graph;end:avfilter_inout_free(inputs);avfilter_inout_free(outputs);return ret;
}static int init_filters(void)
{const char *filter_spec;unsigned int i;int ret;filter_ctx av_malloc_array(ifmt_ctx-nb_streams, sizeof(*filter_ctx));if (!filter_ctx)return AVERROR(ENOMEM);for (i 0; i ifmt_ctx-nb_streams; i) {filter_ctx[i].buffersrc_ctx NULL;filter_ctx[i].buffersink_ctx NULL;filter_ctx[i].filter_graph NULL;if (!(ifmt_ctx-streams[i]-codecpar-codec_type AVMEDIA_TYPE_AUDIO|| ifmt_ctx-streams[i]-codecpar-codec_type AVMEDIA_TYPE_VIDEO))continue;if (ifmt_ctx-streams[i]-codecpar-codec_type AVMEDIA_TYPE_VIDEO)filter_spec null; /* passthrough (dummy) filter for video */elsefilter_spec anull; /* passthrough (dummy) filter for audio */ret init_filter(filter_ctx[i], stream_ctx[i].dec_ctx,stream_ctx[i].enc_ctx, filter_spec);if (ret)return ret;}return 0;
}static int encode_write_frame(AVFrame *filt_frame, unsigned int stream_index, int *got_frame) {int ret;int got_frame_local;AVPacket enc_pkt;int (*enc_func)(AVCodecContext *, AVPacket *, const AVFrame *, int *) (ifmt_ctx-streams[stream_index]-codecpar-codec_type AVMEDIA_TYPE_VIDEO) ? avcodec_encode_video2 : avcodec_encode_audio2;if (!got_frame)got_frame got_frame_local;av_log(NULL, AV_LOG_INFO, Encoding frame\n);/* encode filtered frame */enc_pkt.data NULL;enc_pkt.size 0;av_init_packet(enc_pkt);ret enc_func(stream_ctx[stream_index].enc_ctx, enc_pkt,filt_frame, got_frame);av_frame_free(filt_frame);if (ret 0)return ret;if (!(*got_frame))return 0;/* prepare packet for muxing */enc_pkt.stream_index stream_index;av_packet_rescale_ts(enc_pkt,stream_ctx[stream_index].enc_ctx-time_base,ofmt_ctx-streams[stream_index]-time_base);av_log(NULL, AV_LOG_DEBUG, Muxing frame\n);/* mux encoded frame */ret av_interleaved_write_frame(ofmt_ctx, enc_pkt);return ret;
}static int filter_encode_write_frame(AVFrame *frame, unsigned int stream_index)
{int ret;AVFrame *filt_frame;av_log(NULL, AV_LOG_INFO, Pushing decoded frame to filters\n);/* push the decoded frame into the filtergraph */ret av_buffersrc_add_frame_flags(filter_ctx[stream_index].buffersrc_ctx,frame, 0);if (ret 0) {av_log(NULL, AV_LOG_ERROR, Error while feeding the filtergraph\n);return ret;}/* pull filtered frames from the filtergraph */while (1) {filt_frame av_frame_alloc();if (!filt_frame) {ret AVERROR(ENOMEM);break;}av_log(NULL, AV_LOG_INFO, Pulling filtered frame from filters\n);ret av_buffersink_get_frame(filter_ctx[stream_index].buffersink_ctx,filt_frame);if (ret 0) {/* if no more frames for output - returns AVERROR(EAGAIN)* if flushed and no more frames for output - returns AVERROR_EOF* rewrite retcode to 0 to show it as normal procedure completion*/if (ret AVERROR(EAGAIN) || ret AVERROR_EOF)ret 0;av_frame_free(filt_frame);break;}filt_frame-pict_type AV_PICTURE_TYPE_NONE;ret encode_write_frame(filt_frame, stream_index, NULL);if (ret 0)break;}return ret;
}static int flush_encoder(unsigned int stream_index)
{int ret;int got_frame;if (!(stream_ctx[stream_index].enc_ctx-codec-capabilities AV_CODEC_CAP_DELAY))return 0;while (1) {av_log(NULL, AV_LOG_INFO, Flushing stream #%u encoder\n, stream_index);ret encode_write_frame(NULL, stream_index, got_frame);if (ret 0)break;if (!got_frame)return 0;}return ret;
}int main(int argc, char **argv)
{int ret;AVPacket packet { .data NULL, .size 0 };AVFrame *frame NULL;enum AVMediaType type;unsigned int stream_index;unsigned int i;int got_frame;int (*dec_func)(AVCodecContext *, AVFrame *, int *, const AVPacket *);if (argc ! 3) {av_log(NULL, AV_LOG_ERROR, Usage: %s input file output file\n, argv[0]);return 1;}if ((ret open_input_file(argv[1])) 0)goto end;if ((ret open_output_file(argv[2])) 0)goto end;if ((ret init_filters()) 0)goto end;/* read all packets */while (1) {if ((ret av_read_frame(ifmt_ctx, packet)) 0)break;stream_index packet.stream_index;type ifmt_ctx-streams[packet.stream_index]-codecpar-codec_type;av_log(NULL, AV_LOG_DEBUG, Demuxer gave frame of stream_index %u\n,stream_index);if (filter_ctx[stream_index].filter_graph) {av_log(NULL, AV_LOG_DEBUG, Going to reencodefilter the frame\n);frame av_frame_alloc();if (!frame) {ret AVERROR(ENOMEM);break;}av_packet_rescale_ts(packet,ifmt_ctx-streams[stream_index]-time_base,stream_ctx[stream_index].dec_ctx-time_base);dec_func (type AVMEDIA_TYPE_VIDEO) ? avcodec_decode_video2 :avcodec_decode_audio4;ret dec_func(stream_ctx[stream_index].dec_ctx, frame,got_frame, packet);if (ret 0) {av_frame_free(frame);av_log(NULL, AV_LOG_ERROR, Decoding failed\n);break;}if (got_frame) {frame-pts frame-best_effort_timestamp;ret filter_encode_write_frame(frame, stream_index);av_frame_free(frame);if (ret 0)goto end;} else {av_frame_free(frame);}} else {/* remux this frame without reencoding */av_packet_rescale_ts(packet,ifmt_ctx-streams[stream_index]-time_base,ofmt_ctx-streams[stream_index]-time_base);ret av_interleaved_write_frame(ofmt_ctx, packet);if (ret 0)goto end;}av_packet_unref(packet);}/* flush filters and encoders */for (i 0; i ifmt_ctx-nb_streams; i) {/* flush filter */if (!filter_ctx[i].filter_graph)continue;ret filter_encode_write_frame(NULL, i);if (ret 0) {av_log(NULL, AV_LOG_ERROR, Flushing filter failed\n);goto end;}/* flush encoder */ret flush_encoder(i);if (ret 0) {av_log(NULL, AV_LOG_ERROR, Flushing encoder failed\n);goto end;}}av_write_trailer(ofmt_ctx);
end:av_packet_unref(packet);av_frame_free(frame);for (i 0; i ifmt_ctx-nb_streams; i) {avcodec_free_context(stream_ctx[i].dec_ctx);if (ofmt_ctx ofmt_ctx-nb_streams i ofmt_ctx-streams[i] stream_ctx[i].enc_ctx)avcodec_free_context(stream_ctx[i].enc_ctx);if (filter_ctx filter_ctx[i].filter_graph)avfilter_graph_free(filter_ctx[i].filter_graph);}av_free(filter_ctx);av_free(stream_ctx);avformat_close_input(ifmt_ctx);if (ofmt_ctx !(ofmt_ctx-oformat-flags AVFMT_NOFILE))avio_closep(ofmt_ctx-pb);avformat_free_context(ofmt_ctx);if (ret 0)av_log(NULL, AV_LOG_ERROR, Error occurred: %s\n, av_err2str(ret));return ret ? 1 : 0;
}
参考
http://ffmpeg.org/
