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FFmpeg滤镜代码级分析

分类： LINUX

2012-08-22 10:45:48

前一篇文章《为FFmpeg添加自定义滤镜》详细讲述了FFmpeg的滤镜添加步骤，并给出了代码实例。

本文将以FFmpeg自带的deinterlace滤镜”yadif – yet another deinterlace filter”为例分析

FFmpeg滤镜的代码级实现机制。


总的来说,FFmpeg的滤镜机制和MicroSoft Directshow机制基本相同——不知道谁学了谁的，还是程

序员所见略同：

构建机制上：FFmpeg自己实现了统一的对象模型，DShow是COM的实现;

框架实现上：都使用filter graph来管理滤镜;

连接方式上：FFmpeg使用Pad结构体，DShow使用Pin，两者都是分配器的机制;


下面是以层级来分析代码：

FFmpeg转码层的伪码如下所示，红色粗体是和filter相关的函数:

点击(此处)折叠或打开

  1. int transcode(AVFormatContext **output_files,
  2.               int nb_output_files,
  3.               AVInputFile *input_files,
  4.               int nb_input_files,
  5.               AVStreamMap *stream_maps,
  6.               int nb_stream_maps)
  7. {
  8.   …
  9.   解码参数计算;


  12.   #if CONFIG_AVFILTER
  13.   if (configure_video_filters(ist, ost)) {
  14.     fprintf(stderr, "Error opening filters!\n");
  15.     ret = AVERROR(EINVAL);
  16.     goto fail;
  17.   }
  18.   #endif


  21.   编码参数计算;

  23.   output_packet(ist, ist_index, ost_table,
  24.                 nb_ostreams, &pkt, &errorflag);

  26.   ……

  28.   return ret;
  29. }
函数configure_video_filters是用来初始化filter graph 和filter本身的初始化；

函数output_packet是FFmpeg整个解码，滤镜处理，编码调用的实现。


1. 先来看configure_video_filters的实现：

点击(此处)折叠或打开

  1. int configure_video_filters(AVInputStream *ist,
  2.                             AVOutputStream *ost)
  3. {
  4.    // 类似于directshow一样初始化filter graph等;
  5.   ost->graph = avfilter_graph_alloc();
  6.   …
    // 初始化filter graph和filter
  1.   avfilter_graph_parse(ost->graph, ost->avfilter,
  2.                        &inputs, &outputs, NULL)


  5.   // 检查filter支持的媒体类型
  6.   avfilter_graph_config(ost->graph, NULL);

  8.   。。。

  10.   return 0;
  11. }

filter graph和filter的初始化:

点击(此处)折叠或打开

  1. int avfilter_graph_parse(AVFilterGraph *graph,
  2.                          const char *filters,
  3.                          AVFilterInOut **open_inputs,
  4.                          AVFilterInOut **open_outputs,
  5.                          void *log_ctx)
  6. {

  8.     do {

  10.         parse_inputs(&filters, &curr_inputs, open_outputs, log_ctx);

  12.         parse_filter(&filter, &filters, graph, index, log_ctx);


  15.         if (filter->input_count == 1 && !curr_inputs && !index) {
  16.             /* First input can be omitted if it is "[in]" */
  17.             const char *tmp = "[in]";
  18.             if ((ret = parse_inputs(&tmp, &curr_inputs, open_outputs,
  19.                                     log_ctx)) < 0)
  20.                 goto fail;
  21.         }


  24.         link_filter_inouts(filter, &curr_inputs, open_inputs, log_ctx);


  27.         parse_outputs(&filters, &curr_inputs, open_inputs,
  28.                       open_outputs, log_ctx);


  31.         filters += strspn(filters, WHITESPACES);
  32.         chr = *filters++;

  34.         index++;
  35.     } while (chr == ',' || chr == ';');

  37.     if (open_inputs && *open_inputs &&
  38.         !strcmp((*open_inputs)->name, ""out"") && curr_inputs) {
  39.         /* Last output can be omitted if it is "[out]" */
  40.         const char *tmp = "[out]";
  41.         if ((ret = parse_outputs(&tmp, &curr_inputs, open_inputs,
  42.                                               open_outputs, log_ctx)) < 0)
  43.             goto fail;

  45.     }

  47.     return 0;
  48. }

点击(此处)折叠或打开

  2. static int parse_filter(AVFilterContext **filt_ctx, 
  3.                         const char **buf, AVFilterGraph *graph,"
  4.                         int index, void *log_ctx)
  5. {
  6.     char *opts = NULL;
  7.     char *name = av_get_token(buf, "=,;[\n");
  8.     int ret;

  10.     if (**buf == '=') {
  11.         (*buf)++;
  12.         opts = av_get_token(buf, "[],;\n");
  13.     }

  15.     ret = create_filter(filt_ctx, graph, index, name, opts, log_ctx);

  17.     av_free(name);
  18.     av_free(opts);
  19.     return ret;
  20. }

到了真正的Filter graph初始化，这部分和DShow很相似：

点击(此处)折叠或打开

  1. int create_filter(AVFilterContext **filt_ctx,
  2.                   AVFilterGraph *ctx, int index,
  3.                   const char *filt_name, const char *args,
  4.                   void *log_ctx)

  6. {
  7.     AVFilter *filt;
  8.     char inst_name[30];
  9.     char tmp_args[256];
  10.     int ret;

  12.     // 注册当前filter到静态数组中
  13.     filt = avfilter_get_by_name(filt_name);

  15.     // 分配并初始化输入输出Pad
  16.     ret = avfilter_open(filt_ctx, filt, inst_name);

  18.     // 将当前filter添加到filter graph中
  19.     ret = avfilter_graph_add_filter(ctx, *filt_ctx);

  21.     // 通过函数指针，调用当前filter的初始化函数
  22.     ret = avfilter_init_filter(*filt_ctx, args, NULL);
  23.     return 0;
  24. }

点击(此处)折叠或打开

  1. int avfilter_init_filter(AVFilterContext *filter,
  2.                          const char *args,
  3.                          void *opaque)
  4. {
  5.     int ret=0;

  7.     if (filter->filter->init)
  8.         ret = filter->filter->init(filter, args, opaque);
  9.     return ret;
  10. }

点击(此处)折叠或打开

  1. static av_cold int init(AVFilterContext *ctx,
  2.                                   const char *args,
  3.                                   void *opaque)
  4. {
  5.     YADIFContext *yadif = ctx->priv;
  6.     av_unused int cpu_flags = av_get_cpu_flags();

  8.     yadif->mode = 0;
  9.     yadif->parity = -1;
  10.     yadif->csp = NULL;

  12.     // 滤镜函数指针初始化赋值
  13.     yadif->filter_line = filter_line_c;

  15.     return 0;
  16. }

2. 接着来看两个filter的Pad连接时的媒体类型的协商机制


点击(此处)折叠或打开

  1. int avfilter_graph_config(AVFilterGraph *graphctx, void *log_ctx)
  2. {
  3.     int ret;
     // 检查filter的权限
  1.     if ((ret = ff_avfilter_graph_check_validity(graphctx, log_ctx)))
  2.         return ret;
  3.     
  4.     // 检查Pad支持的媒体类型
  5.     if ((ret = ff_avfilter_graph_config_formats(graphctx, log_ctx)))
  6.         return ret;
     // 
  1.     if ((ret = ff_avfilter_graph_config_links(graphctx, log_ctx)))
  2.         return ret;

  4.     return 0;
  5. }

检查Pad支持的媒体类型 :

点击(此处)折叠或打开

  1. int ff_avfilter_graph_config_formats(AVFilterGraph *graph,
  2.                                                           AVClass *log_ctx)
  3. {
  4.     int ret;

  6.     /* find supported formats from sub-filters, and merge along links */
  7.     if ((ret = query_formats(graph, log_ctx)) < 0)
  8.         return ret;

  10.     /* Once everything is merged, it's possible that we'll still have
  11.      * multiple valid media format choices. We pick the first one. */
  12.     pick_formats(graph);

  14.     return 0;
  15. }

点击(此处)折叠或打开

  1. static int query_formats(AVFilterGraph *graph,
  2.                          AVClass *log_ctx)
  3. {
  4.     int i, j, ret;
  5.     int scaler_count = 0;
  6.     char inst_name[30];

  8.     /* ask all the sub-filters for their supported media formats */
  9.     for (i = 0; i < graph->filter_count; i++) {
  10.         if (graph->filters[i]->filter->query_formats)
  11.             graph->filters[i]->filter->query_formats(graph->filters[i]);
  12.         else
  13.             avfilter_default_query_formats(graph->filters[i]);
  14.     }

  16.     /* go through and merge as many format lists as possible */
  17.     for (i = 0; i < graph->filter_count; i++) {

  19.        …
  20.     
  21.     }

  23.     return 0;
  24. }

点击(此处)折叠或打开

  1. /* 检查连接用Pad支持的媒体类型 */
  2. static int query_formats(AVFilterContext *ctx)
  3. {
  4.     static const enum PixelFormat pix_fmts[] = {
  5.         PIX_FMT_YUV420P,
  6.         PIX_FMT_YUV422P,
  7.         PIX_FMT_YUV444P,
  8.         PIX_FMT_YUV410P,
  9.         PIX_FMT_YUV411P,
  10.         PIX_FMT_GRAY8,
  11.         PIX_FMT_YUVJ420P,
  12.         PIX_FMT_YUVJ422P,
  13.         PIX_FMT_YUVJ444P,
  14.         AV_NE( PIX_FMT_GRAY16BE, PIX_FMT_GRAY16LE ),
  15.         PIX_FMT_YUV440P,
  16.         PIX_FMT_YUVJ440P,
  17.         AV_NE( PIX_FMT_YUV420P16BE, PIX_FMT_YUV420P16LE ),
  18.         AV_NE( PIX_FMT_YUV422P16BE, PIX_FMT_YUV422P16LE ),
  19.         AV_NE( PIX_FMT_YUV444P16BE, PIX_FMT_YUV444P16LE ),
  20.         PIX_FMT_NONE
  21.     };

  23.     avfilter_set_common_pixel_formats(ctx,
  24.                                       avfilter_make_format_list(pix_fmts));

  26.     return 0;
  27. }
3. 最后来看滤镜的连接和对每帧图像处理时的调用

点击(此处)折叠或打开

  1. int output_packet(AVInputStream *ist, int ist_index,
  2.                   AVOutputStream **ost_table,
  3.                   int nb_ostreams,
  4.                   const AVPacket *pkt,
  5.                   int *errorflag)
  6. {

  8.   /* decode the packet if needed */
  9.   if (ist->decoding_needed) {

  11.     解码;

  13. #if CONFIG_AVFILTER
  14.     if(ist->st->codec->codec_type == AVMEDIA_TYPE_VIDEO)
  15.     if (start_time == 0 || ist->pts >= start_time) {
  16.       for(i=0;i<nb_ostreams;i++) {
  17.         ost = ost_table[i];
  18.         if (ost->input_video_filter && ost->source_index == ist_index) {
  19.           if (!picture.sample_aspect_ratio.num)
  20.           picture.sample_aspect_ratio = ist->st->sample_aspect_ratio;
  21.           picture.pts = ist->pts;

  23.           av_vsrc_buffer_add_frame(ost->input_video_filter, &picture, AV_VSRC_BUF_FLAG_OVERWRITE);

  25.         }
  26.       }
  27.     }
  28. #endif

  30. #if CONFIG_AVFILTER
  31.     frame_available = ist->st->codec->codec_type
  32.                       != AVMEDIA_TYPE_VIDEO ||
  33.                       !ost->output_video_filter ||
  34.                       avfilter_poll_frame(ost->output_video_filter->inputs[0]);
  35.     while (frame_available) {
  36.       if (ist->st->codec->codec_type == AVMEDIA_TYPE_VIDEO &&
  37.           ost->output_video_filter) {
  38.         AVRational ist_pts_tb = ost->output_video_filter->inputs[0]->time_base;
  39.         if (av_vsink_buffer_get_video_buffer_ref(ost->output_video_filter,
  40.             &ost->picref, 0) < 0)
  41.           goto cont;
  42.         if (ost->picref) {
  43.           AVRational tempVar = {1, AV_TIME_BASE};
  44.           avfilter_fill_frame_from_video_buffer_ref(&picture, ost->picref);
  45.           //ist->pts = av_rescale_q(ost->picref->pts, ist_pts_tb, AV_TIME_BASE_Q);
  46.           ist->pts = av_rescale_q(ost->picref->pts, ist_pts_tb, tempVar);//modify by chenrui
  47.         }
  48.       }
  49. #endif

  51.       编码;

  53.       return 0;
  54.       fail_decode:
  55.       return -1;
  56.    }
  57.   }
  58. }
先来看滤镜的连接：


点击(此处)折叠或打开

  2. int av_vsrc_buffer_add_frame(AVFilterContext *buffer_src,
  3.                              const AVFrame *frame, int flags)
  4. {
  5.     // 从帧列表中得到当前帧
  6.     AVFilterBufferRef *picref =
  7.         avfilter_get_video_buffer_ref_from_frame(frame, 
  8.                                                  AV_PERM_WRITE);
  9.     if (!picref)
  10.         return AVERROR(ENOMEM);
  11.     ret = av_vsrc_buffer_add_video_buffer_ref(buffer_src, 
  12.                                               picref, flags);


  15.     picref->buf->data[0] = NULL;
  16.     avfilter_unref_buffer(picref);

  18.     return ret;
  19. }


  22. int av_vsrc_buffer_add_video_buffer_ref(AVFilterContext *buffer_filter,
  23.                                         AVFilterBufferRef *picref, int flags)"
  24. {

  26.     智能插入相应的filter; 

  28.     c->picref = avfilter_get_video_buffer(outlink, AV_PERM_WRITE,
  29.                                           picref->video->w, picref->video->h);

  31.     av_image_copy(c->picref->data, c->picref->linesize,
  32.                   picref->data, picref->linesize,
  33.                   picref->format, picref->video->w, picref->video->h);
  34.     avfilter_copy_buffer_ref_props(c->picref, picref);

  36.     return 0;
  37. }


  40. AVFilterBufferRef *avfilter_get_video_buffer(AVFilterLink *link,
  41.                                       int perms, int w, int h)
  42. {
  43.     AVFilterBufferRef *ret = NULL;

  45.     if (link->dstpad->get_video_buffer)
  46.         ret = link->dstpad->get_video_buffer(link, perms, w, h);

  48.     if (!ret)
  49.         ret = avfilter_default_get_video_buffer(link, perms, w, h);

  51.     if (ret)
  52.         ret->type = AVMEDIA_TYPE_VIDEO;

  54.     return ret;
  55. }

  57. AVFilterBufferRef *get_video_buffer(AVFilterLink *link, int perms, 
  58.                                     int w, int h)
  59. {
  60.     AVFilterBufferRef *picref;
  61.     int width = FFALIGN(w, 32);
  62.     int height= FFALIGN(h+2, 32);
  63.     int i;

  65.     picref = avfilter_default_get_video_buffer(link, perms, width, height);

  67.     picref->video->w = w;
  68.     picref->video->h = h;

  70.     for (i = 0; i < 3; i++)
  71.         picref->data[i] += picref->linesize[i];

  73.     return picref;
  74. }
最后来看图像处理函数的实现：


点击(此处)折叠或打开

  1. int avfilter_poll_frame(AVFilterLink *link)
  2. {
  3.     int i, min = INT_MAX;

  5.     if (link->srcpad->poll_frame)
  6.         return link->srcpad->poll_frame(link);
  7.     for (i = 0; i < link->src->input_count; i++) {
  8.         int val;
  9.         if (!link->src->inputs[i])
  10.             return -1;
  11.         val = avfilter_poll_frame(link->src->inputs[i]);
  12.         min = FFMIN(min, val);
  13.     }

  15.     return min;
  16. }


  19. int poll_frame(AVFilterLink *link)
  20. {
  21.     YADIFContext *yadif = link->src->priv;
  22.     int ret, val;

  24.     if (yadif->frame_pending)
  25.         return 1;

  27.     val = avfilter_poll_frame(link->src->inputs[0]);

  29.     if (val==1 && !yadif->next) {
  30.       //FIXME change API to not requre this red tape
  31.       if ((ret = avfilter_request_frame(link->src->inputs[0])) < 0)
  32.         return ret;
  33.       val = avfilter_poll_frame(link->src->inputs[0]);
  34.     }
  35.     assert(yadif->next || !val);

  37.     return val * ((yadif->mode&1)+1);
  38. }

  40. int avfilter_request_frame(AVFilterLink *link)
  41. {


  44.     if (link->srcpad->request_frame)
  45.         return link->srcpad->request_frame(link);
  46.     else if (link->src->inputs[0])
  47.         return avfilter_request_frame(link->src->inputs[0]);
  48.     else return -1;
  49. }



  53. static int request_frame(AVFilterLink *link)
  54. {
  55.     BufferSourceContext *c = link->src->priv;

  57.     if (!c->picref) {
  58.         av_log(link->src, AV_LOG_WARNING,
  59.                "request_frame() called with no available frame!\n");
  60.         return AVERROR(EINVAL);
  61.     }
     // 图像处理函数的真正实现
  1.     avfilter_start_frame(link, avfilter_ref_buffer(c->picref, ~0));
  2.     avfilter_draw_slice(link, 0, link->h, 1);
  3.     avfilter_end_frame(link);

  5.     avfilter_unref_buffer(c->picref);
  6.     c->picref = NULL;

  8.     return 0;
  9. }
完结。

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