本文共 16686 字,大约阅读时间需要 55 分钟。
init()
query_format(); // 输入输出的格式查询: 列出滤镜支持的格式列表
config_input();
config_output();
for (;;) {
request_frame();
filter_frame();
}
uninit();
STEP1: init(); // 滤镜初始化 : 用于初始化滤镜#0 init (ctx=0x24dbe40) at libavfilter/vf_delogo.c:196#1 0x00000000004e9ad5 in avfilter_init_str (filter=0x24dbe40, args=0x24dbdc0 "x=10:y=10:w=80:h=20") at libavfilter/avfilter.c:1018#2 0x00000000004fb54a in create_filter (filt_ctx=0x7fffffffce20, ctx=0x24da800, index=, name= , args=0x24dbdc0 "x=10:y=10:w=80:h=20", log_ctx=0x24da800) at libavfilter/graphparser.c:149#3 0x00000000004fbee2 in parse_filter (graph=0x24da800, filters=0x23a5488 "", inputs=0x7fffffffd0b8, outputs=0x7fffffffd0b0) at libavfilter/graphparser.c:192#4 avfilter_graph_parse2 (graph=0x24da800, filters=0x23a5488 "", inputs=0x7fffffffd0b8, outputs=0x7fffffffd0b0) at libavfilter/graphparser.c:427#5 0x00000000004bc528 in configure_filtergraph (fg=0x23a5500) at fftools/ffmpeg_filter.c:1047#6 0x00000000004cb4ba in ifilter_send_frame (ifilter=0x23aabc0, frame=0x24b2480) at fftools/ffmpeg.c:2173#7 0x00000000004cb9b6 in send_frame_to_filters (ist=0x23adfc0, pkt= , got_output= , duration_pts=0x7fffffffd570, eof= , decode_failed=0x7fffffffd578) at fftools/ffmpeg.c:2254#8 decode_video (ist=0x23adfc0, pkt= , got_output= , duration_pts=0x7fffffffd570, eof= , decode_failed=0x7fffffffd578) at fftools/ffmpeg.c:2455#9 0x00000000004cc1ad in process_input_packet (ist=0x23adfc0, pkt= , no_eof=0) at fftools/ffmpeg.c:2609#10 0x00000000004ce659 in process_input () at fftools/ffmpeg.c:4441#11 transcode_step () at fftools/ffmpeg.c:4561#12 0x00000000004d0e65 in transcode (argc= , argv= ) at fftools/ffmpeg.c:4615#13 main (argc= , argv= ) at fftools/ffmpeg.c:4847preinit(); // 滤镜预初始化: 用于分配空间和初始化子对象STEP2: query_format(); // 输入输出的格式查询: 列出滤镜支持的格式列表#0 query_formats (ctx=0x24dbe40) at libavfilter/vf_delogo.c:188#1 0x00000000004ec8e6 in filter_query_formats (ctx=0x24dbe40) at libavfilter/avfiltergraph.c:326#2 0x00000000004ed014 in query_formats (graph=0x24da800, log_ctx=0x0) at libavfilter/avfiltergraph.c:454#3 0x00000000004edc51 in graph_config_formats (graphctx=0x24da800, log_ctx=0x0) at libavfilter/avfiltergraph.c:1163#4 avfilter_graph_config (graphctx=0x24da800, log_ctx=0x0) at libavfilter/avfiltergraph.c:1274#5 0x00000000004bcabb in configure_filtergraph (fg=0x23a5500) at fftools/ffmpeg_filter.c:1100#6 0x00000000004cb4ba in ifilter_send_frame (ifilter=0x23aabc0, frame=0x24b2480) at fftools/ffmpeg.c:2173#7 0x00000000004cb9b6 in send_frame_to_filters (ist=0x23adfc0, pkt= , got_output= , duration_pts=0x7fffffffd570, eof= , decode_failed=0x7fffffffd578) at fftools/ffmpeg.c:2254#8 decode_video (ist=0x23adfc0, pkt= , got_output= , duration_pts=0x7fffffffd570, eof= , decode_failed=0x7fffffffd578) at fftools/ffmpeg.c:2455#9 0x00000000004cc1ad in process_input_packet (ist=0x23adfc0, pkt= , no_eof=0) at fftools/ffmpeg.c:2609#10 0x00000000004ce659 in process_input () at fftools/ffmpeg.c:4441#11 transcode_step () at fftools/ffmpeg.c:4561#12 0x00000000004d0e65 in transcode (argc= , argv= ) at fftools/ffmpeg.c:4615#13 main (argc= , argv= ) at fftools/ffmpeg.c:4847STEP3: 配置滤镜的输入、输出格式和参数 config_input(); config_output();#0 config_input (inlink=0x24dd980) at libavfilter/vf_delogo.c:231#1 0x00000000004ea930 in avfilter_config_links (filter=0x24dbe40) at libavfilter/avfilter.c:369#2 0x00000000004ea8b0 in avfilter_config_links (filter=0x24da900) at libavfilter/avfilter.c:307#3 0x00000000004ea8b0 in avfilter_config_links (filter=0x24dec40) at libavfilter/avfilter.c:307#4 0x00000000004ee922 in graph_config_links (graphctx=0x24da800, log_ctx=0x0) at libavfilter/avfiltergraph.c:261#5 avfilter_graph_config (graphctx=0x24da800, log_ctx=0x0) at libavfilter/avfiltergraph.c:1276#6 0x00000000004bcabb in configure_filtergraph (fg=0x23a5500) at fftools/ffmpeg_filter.c:1100#7 0x00000000004cb4ba in ifilter_send_frame (ifilter=0x23aabc0, frame=0x24b2480) at fftools/ffmpeg.c:2173#8 0x00000000004cb9b6 in send_frame_to_filters (ist=0x23adfc0, pkt= , got_output= , duration_pts=0x7fffffffd570, eof= , decode_failed=0x7fffffffd578) at fftools/ffmpeg.c:2254#9 decode_video (ist=0x23adfc0, pkt= , got_output= , duration_pts=0x7fffffffd570, eof= , decode_failed=0x7fffffffd578) at fftools/ffmpeg.c:2455#10 0x00000000004cc1ad in process_input_packet (ist=0x23adfc0, pkt= , no_eof=0) at fftools/ffmpeg.c:2609#11 0x00000000004ce659 in process_input () at fftools/ffmpeg.c:4441#12 transcode_step () at fftools/ffmpeg.c:4561#13 0x00000000004d0e65 in transcode (argc= , argv= ) at fftools/ffmpeg.c:4615#14 main (argc= , argv= ) at fftools/ffmpeg.c:4847STEP4: 滤镜体对每一帧数据进行处理 filter_frame();#0 filter_frame (inlink=0x24dd980, in=0x24de480) at libavfilter/vf_delogo.c:245#1 0x00000000004eb92e in ff_filter_frame_framed (filter= ) at libavfilter/avfilter.c:1071#2 ff_filter_frame_to_filter (filter= ) at libavfilter/avfilter.c:1219#3 ff_filter_activate_default (filter= ) at libavfilter/avfilter.c:1268#4 ff_filter_activate (filter= ) at libavfilter/avfilter.c:1430#5 0x00000000004efad0 in push_frame (ctx= , frame=0x24b2480, flags= ) at libavfilter/buffersrc.c:181#6 av_buffersrc_add_frame_internal (ctx= , frame=0x24b2480, flags= ) at libavfilter/buffersrc.c:255#7 0x00000000004efc2f in av_buffersrc_add_frame_flags (ctx=0x24ddcc0, frame= , flags= ) at libavfilter/buffersrc.c:164#8 0x00000000004cb39d in ifilter_send_frame (ifilter=0x23aabc0, frame=0x24b2480) at fftools/ffmpeg.c:2180#9 0x00000000004cb9b6 in send_frame_to_filters (ist=0x23adfc0, pkt= , got_output= , duration_pts=0x7fffffffd570, eof= , decode_failed=0x7fffffffd578) at fftools/ffmpeg.c:2254#10 decode_video (ist=0x23adfc0, pkt= , got_output= , duration_pts=0x7fffffffd570, eof= , decode_failed=0x7fffffffd578) at fftools/ffmpeg.c:2455#11 0x00000000004cc1ad in process_input_packet (ist=0x23adfc0, pkt= , no_eof=0) at fftools/ffmpeg.c:2609#12 0x00000000004ce659 in process_input () at fftools/ffmpeg.c:4441#13 transcode_step () at fftools/ffmpeg.c:4561#14 0x00000000004d0e65 in transcode (argc= , argv= ) at fftools/ffmpeg.c:4615#15 main (argc= , argv= ) at fftools/ffmpeg.c:4847STEP5: uninit()
5.3.1. decode_video //ffmpeg.c最初的源头,是ffmpeg.c的decode_video函数。 核心代码如下所示:static int decode_video(InputStream *ist, AVPacket *pkt, int *got_output){ AVFrame* decoded_frame, f; //解码 ret = avcodec_decode_video2(ist->dec_ctx, decoded_frame, got_output, pkt); //...... //将解码后的帧数据 送给滤镜 for (i = 0; i < ist->nb_filters; i++) { f = decodec_frame; ret = av_buffersrc_add_frame_flags(ist->filters[i]->filter, f, AV_BUFFERSRC_FLAG_PUSH); }}可见,最重要做2件事,一个解码,一个送给滤镜。 送给哪个滤镜呢?InputStream *ist的nb_filters为1,其实就是指向名字为“buffer”的filter(源文件:buffersrc.c)。这个filter与其他filter不同的是,它是所有filter的第一个入口。解码完,都先给它,它再传递给下一个。为啥先给他呢?很简单,它是一个FIFO,缓存数据用的。5.3.2. av_buffersrc_add_frame_flags//buffersrc.c该函数直接走到av_buffersrc_add_frame_internal //buffersrc.c5.3.3. av_buffersrc_add_frame_internal //buffersrc.cstatic int av_buffersrc_add_frame_internal(AVFilterContext *ctx, AVFrame *frame, int flags){ AVFrame *copy = NULL; av_frame_ref(copy, frame); // 将解码后的帧数据 frame 写FIFO av_fifo_generic_write(s->fifo, ©, sizeof(copy), NULL); // if ((flags & AV_BUFFERSRC_FLAG_PUSH)) if ((ret = ctx->output_pads[0].request_frame(ctx->outputs[0])) < 0) return ret; return 0;}可见, 该函数把frame写到FIFO,然后调了自己的output_pads[0]的request_frame。5.3.4. request_frame //buffersrc.cstatic int request_frame(AVFilterLink *link){ BufferSourceContext *c = link->src->priv; AVFrame *frame; int ret; //省略...... // 从FIFO中读取一帧数据 av_fifo_generic_read(c->fifo, &frame, sizeof(frame), NULL); av_log(NULL, AV_LOG_WARNING, "request_frame, frame-pts %lld \n", frame->pts); //这个link,是第一个link,链接当前的AVFilterContext和下一个AVFilterContext,也就用户设置的真正要用的滤镜代码 ret = ff_filter_frame(link, frame); return ret;}可见它从FIFO读取一帧数据。然后调用ff_filter_frame。此时输入的link是第一个AVFilterLink。5.3.5. ff_filter_frame // avfilter.c该函数做了一些基本检查,走到ff_filter_frame_framed5.3.6. ff_filter_frame_framed //avfilter.c{ //定义一个函数指针filter_frame。所指向的函数,参数为AVFilterLink *, AVFrame *,返回值为int int (*filter_frame)(AVFilterLink *, AVFrame *); //下一个AVFilterContext,对本例来说,就是我们自己写的transform 滤镜,源码在vf_transform.c AVFilterContext *dstctx = link->dst; AVFilterPad *dst = link->dstpad; AVFrame *out = NULL; int ret; //函数指针filter_frame,link->dstpad其实就是dstctx->input_pads,也就是transform滤镜定义的 if (!(filter_frame = dst->filter_frame)) filter_frame = default_filter_frame; //省略300字 ret = filter_frame(link, out); link->frame_count++; ff_update_link_current_pts(link, pts); return ret;}定义一个函数指针filter_frame。所指向的函数,必须是参数为(AVFilterLink , AVFrame ) ,返回值为int filter_frame = dst->filter_frame dst = link->dstpad,而link->dstpad就是transform过滤器定义的input_padsstatic const AVFilterPad avfilter_vf_transform_inputs[] = { { .name = "default", .type = AVMEDIA_TYPE_VIDEO, .filter_frame = filter_frame, }, { NULL }};所以,filter_frame函数指针,指向的就是vf_transform.c实现的filter_frame函数。5.3.7. filter_frame //vf_transform.c,当然啦,ffmpeg定义的各种filter,比如vf_colorbalance.c,vf_scale.c等,也有这个函数,流程一样的static int filter_frame(AVFilterLink *link, AVFrame *in){ AVFilterContext *avctx = link->dst; //第一个link的dst AVFilterContext,其实就是当前的filter的AVFilterContext AVFilterLink *outlink = avctx->outputs[0]; //当前的AVFilterContext,outputs[0]指向第二个AVFilterLink AVFrame *out; //分配一个空的AVFrame。 out = ff_get_video_buffer(outlink, outlink->w, outlink->h); if (!out) { av_frame_free(&in); return AVERROR(ENOMEM); } //分配的空buffer的参数和上一个基本一致,但修改宽高。当然啦,如果你愿意,不修改宽高,那就不需要下面2句。 av_frame_copy_props(out, in); out->width = outlink->w; out->height = outlink->h; out->format = outlink->format; ThreadData td; td.in = in; td.out = out; int res; if(res = avctx->internal->execute(avctx, do_conversion, &td, NULL, FFMIN(outlink->h, avctx->graph->nb_threads))) { return res; }//启用一个子线程,执行比较耗时的变换。do_conversion是我们要做的变换。 av_frame_free(&in); // 此时的ff_filter_frame,输入参数和前面buffersrc.c调用的已经不一样。outlink是第二个AVFilterLink,buffer也是做了变换的新的buffer return ff_filter_frame(outlink, out); }通过ff_get_video_buffer,分配一个空buffer,该buffer用于存储变换的结果,并会通过ff_filter_frame传递到下一个filter。 do_conversion是一个真正做变换的函数,但其实如果要做的处理并不耗时,也不一定要用另一个线程来处理。直接在该filter_frame做也行。 处理好的新的数据,放在out,调用ff_filter_frame,传递给下一个filter。注意,ff_filter_frame的oulink,对应上图的第二个AVFilterLink。5.3.8. 再次走进ff_filter_frame // avfilter.c如上已知,ff_filter_frame只做了一些基本检查,走到ff_filter_frame_framed。故而我们直接看ff_filter_frame_framedstatic int ff_filter_frame_framed(AVFilterLink *link, AVFrame *frame){ //定义一个函数指针filter_frame。所指向的函数,参数为AVFilterLink *, AVFrame *,返回值为int int (*filter_frame)(AVFilterLink *, AVFrame *); //下一个AVFilterContext,对本例来说,就是系统默认的第三个滤镜,名字叫"format",源码在vf_format.c AVFilterContext *dstctx = link->dst; AVFilterPad *dst = link->dstpad; AVFrame *out = NULL; int ret; if (!(filter_frame = dst->filter_frame)) //vf_format.c没有实现filter函数,因为返回为空 filter_frame = default_filter_frame; //所以函数会走到这,函数指针filter_frame 将指向default_filter_frame //省略300字 ret = filter_frame(link, out); link->frame_count++; ff_update_link_current_pts(link, pts); return ret;}如注释所说,由于vf_format.c没有实现filter函数,所以此时的filter_frame指针,指向的是defalut_filter_frame。5.3.9. default_filter_frame //avfilter.cstatic int default_filter_frame(AVFilterLink *link, AVFrame *frame){ //该函数没干啥,又调用ff_filter_frame了,第一个参数,换成第三个AVFilterLink了,第二个参数不变,frame默默的传递出去 return ff_filter_frame(link->dst->outputs[0], frame);}此时link->dst->outputs[0]对应上图第三个AVFilterLink。5.3.10. 第三次走进ff_filter_frame // avfilter.cstatic int ff_filter_frame_framed(AVFilterLink *link, AVFrame *frame){ //定义一个函数指针filter_frame。所指向的函数,参数为AVFilterLink *, AVFrame *,返回值为int int (*filter_frame)(AVFilterLink *, AVFrame *); //下一个AVFilterContext,对本例来说,就是系统默认的最后一个滤镜,名字叫"buffersink",源码在bufffersink.c AVFilterContext *dstctx = link->dst; AVFilterPad *dst = link->dstpad; AVFrame *out = NULL; int ret; if (!(filter_frame = dst->filter_frame)) //指向buffersink.c实现的filte_frame函数 filter_frame = default_filter_frame; //省略300字 ret = filter_frame(link, out); link->frame_count++; ff_update_link_current_pts(link, pts); return ret;}此时的filter_frame指针,指向buffersink.c实现的filter_frame函数5.3.11. filter_frame //buffersink.cstatic int filter_frame(AVFilterLink *link, AVFrame *frame){ AVFilterContext *ctx = link->dst; BufferSinkContext *buf = link->dst->priv; int ret; if ((ret = add_buffer_ref(ctx, frame)) < 0) return ret; //省略300字 return 0;}static int add_buffer_ref(AVFilterContext *ctx, AVFrame *ref){ BufferSinkContext *buf = ctx->priv; /* cache frame */ //把buffer存到FIFO av_fifo_generic_write(buf->fifo, &ref, FIFO_INIT_ELEMENT_SIZE, NULL); return 0;}很清晰的看到,其实就是把buffer存到FIFO。至此,把filter_frame的来龙去脉搞清楚啦
当我们写了一个filter,把视频做处理后,ffmpeg是如何把它编码的呢?
通过研究,发现编码的源头函数是reap_filters(…),它会被transcode_step(…)函数调用。
5.4.1. reap_filters //ffmpeg.cstatic int reap_filters(int flush){ AVFrame *filtered_frame = NULL;//该指针将存储一个经过滤镜处理后的buffer,并送给encoder int i; /* Reap all buffers present in the buffer sinks */ for (i = 0; i < nb_output_streams; i++) {//一路video,一路audio,那么nb_output_streams = 2 OutputStream *ost = output_streams[i]; OutputFile *of = output_files[ost->file_index]; AVFilterContext *filter; AVCodecContext *enc = ost->enc_ctx; int ret = 0; if (!ost->filter) continue; filter = ost->filter->filter;//OutputStream的filter指针指向buffersink.c定义的AVFilterContext。也就是本文讨论的,最后一个AVFilterContext if (!ost->filtered_frame && !(ost->filtered_frame = av_frame_alloc())) { return AVERROR(ENOMEM); } filtered_frame = ost->filtered_frame; while (1) { double float_pts = AV_NOPTS_VALUE; // this is identical to filtered_frame.pts but with higher precision //av_buffersink_get_frame_flags定义在buffersink.c,用于从FIFO读出一帧 ret = av_buffersink_get_frame_flags(filter, filtered_frame, AV_BUFFERSINK_FLAG_NO_REQUEST); if (ret < 0) { //省略,检查ret //如果ret<0,不是别的错误,那认为还没有数据,跳出循环 break; } switch (filter->inputs[0]->type) { case AVMEDIA_TYPE_VIDEO: //do_video_out函数将会做video编码 do_video_out(of->ctx, ost, filtered_frame, float_pts); break; case AVMEDIA_TYPE_AUDIO: //do_audio_out函数将会做audioo编码 do_audio_out(of->ctx, ost, filtered_frame); break; default: // TODO support subtitle filters av_assert0(0); } av_frame_unref(filtered_frame); } } return 0;}前一节说了,filter_frame(…)的最终结果是,把buffer存在了buffersink.c的FIFO里。 那么,这一节,说的其实就是一个从buffersink的FIFO读数据,并编码的过程。 从上面可知,av_buffersink_get_frame_flags函数,从buffersink读取一帧数据,放到filtered_frame。5.4.2. do_video_out //ffmpeg.cstatic void do_video_out(AVFormatContext *s, OutputStream *ost, AVFrame *next_picture, double sync_ipts){ int ret; AVCodecContext *enc = ost->enc_ctx; int nb_frames, nb0_frames, i; //省略300字 for (i = 0; i < nb_frames; i++) { AVFrame *in_picture; if (i < nb0_frames && ost->last_frame) { in_picture = ost->last_frame; } else in_picture = next_picture; //省略300字 ost->frames_encoded++; //开始编码 ret = avcodec_encode_video2(enc, &pkt, in_picture, &got_packet); } ///省略300字}该函数很长,做了很多杂事,但关键代码就是调用编码函数avcodec_encode_video2
下面给出ffmpeg使用filter时的函数流程图,主要把和filter相关的函数拉出来!
图7: ffmpeg带filter的流程图
ffmpeg常规的avcodec_register_all(…), avfilter_register_all(…), av_register_all(…)等函数用于注册各种资源
transcode_init() : 主要用于初始化前文提到的各种结构体。
transcode_step : 主要工作: 解码->送filter过滤->编码->继续解码….
choose_output() : 用于选择一个OutputStream。比如有一个audio,一个video,那要根据pts策略,比如谁的pts比较小,就挑哪个OutputStream先干活。
transcode_frome_filter() : 用于选个一个InputStream,用于下一步的process_input()。
process_input() : 主要是解码,并把解码的buffer送往filter处理。
reap_filters() : 主要是,从filter的FIFO拿出buffer,并编码。
FFmpeg官网: http://www.ffmpeg.org
FFmpeg doc : http://www.ffmpeg.org/documentation.html
FFmpeg wiki : https://trac.ffmpeg.org/wiki
CSDN大牛:
转载地址:http://knctd.baihongyu.com/