http://blog.chinaunix.net/uid-26000296-id-3322071.html
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:
- int transcode(AVFormatContext **output_files,
- int nb_output_files,
- AVInputFile *input_files,
- int nb_input_files,
- AVStreamMap *stream_maps,
- int nb_stream_maps)
- {
- …
- 解码参数计算;
- #if CONFIG_AVFILTER
- if (configure_video_filters(ist, ost)) {
- fprintf(stderr, "Error opening filters!\n");
- ret = AVERROR(EINVAL);
- goto fail;
- }
- #endif
- 编码参数计算;
- output_packet(ist, ist_index, ost_table,
- nb_ostreams, &pkt, &errorflag);
- ……
- return ret;
- }
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:
- int configure_video_filters(AVInputStream *ist,
- AVOutputStream *ost)
- {
- // 类似于directshow一样初始化filter graph等;
- ost->graph = avfilter_graph_alloc();
- …
// 初始化filter graph和filter
- avfilter_graph_parse(ost->graph, ost->avfilter,
- &inputs, &outputs, NULL)
- // 检查filter支持的媒体类型
- avfilter_graph_config(ost->graph, NULL);
- 。。。
- return 0;
- }
filter graph和filter的初始化:
- int avfilter_graph_parse(AVFilterGraph *graph,
- const char *filters,
- AVFilterInOut **open_inputs,
- AVFilterInOut **open_outputs,
- void *log_ctx)
- {
- do {
- parse_inputs(&filters, &curr_inputs, open_outputs, log_ctx);
- parse_filter(&filter, &filters, graph, index, log_ctx);
- if (filter->input_count == 1 && !curr_inputs && !index) {
- /* First input can be omitted if it is "[in]" */
- const char *tmp = "[in]";
- if ((ret = parse_inputs(&tmp, &curr_inputs, open_outputs,
- log_ctx)) < 0)
- goto fail;
- }
- link_filter_inouts(filter, &curr_inputs, open_inputs, log_ctx);
- parse_outputs(&filters, &curr_inputs, open_inputs,
- open_outputs, log_ctx);
- filters += strspn(filters, WHITESPACES);
- chr = *filters++;
- index++;
- } while (chr == ',' || chr == ';');
- if (open_inputs && *open_inputs &&
- !strcmp((*open_inputs)->name, ""out"") && curr_inputs) {
- /* Last output can be omitted if it is "[out]" */
- const char *tmp = "[out]";
- if ((ret = parse_outputs(&tmp, &curr_inputs, open_inputs,
- open_outputs, log_ctx)) < 0)
- goto fail;
- }
- return 0;
- }
- static int parse_filter(AVFilterContext **filt_ctx,
- const char **buf, AVFilterGraph *graph,"
- int index, void *log_ctx)
- {
- char *opts = NULL;
- char *name = av_get_token(buf, "=,;[\n");
- int ret;
- if (**buf == '=') {
- (*buf)++;
- opts = av_get_token(buf, "[],;\n");
- }
- ret = create_filter(filt_ctx, graph, index, name, opts, log_ctx);
- av_free(name);
- av_free(opts);
- return ret;
- }
到了真正的Filter graph初始化,这部分和DShow很相似:
- int create_filter(AVFilterContext **filt_ctx,
- AVFilterGraph *ctx, int index,
- const char *filt_name, const char *args,
- void *log_ctx)
- {
- AVFilter *filt;
- char inst_name[30];
- char tmp_args[256];
- int ret;
- // 注册当前filter到静态数组中
- filt = avfilter_get_by_name(filt_name);
- // 分配并初始化输入输出Pad
- ret = avfilter_open(filt_ctx, filt, inst_name);
- // 将当前filter添加到filter graph中
- ret = avfilter_graph_add_filter(ctx, *filt_ctx);
- // 通过函数指针,调用当前filter的初始化函数
- ret = avfilter_init_filter(*filt_ctx, args, NULL);
- return 0;
- }
- int avfilter_init_filter(AVFilterContext *filter,
- const char *args,
- void *opaque)
- {
- int ret=0;
- if (filter->filter->init)
- ret = filter->filter->init(filter, args, opaque);
- return ret;
- }
- static av_cold int init(AVFilterContext *ctx,
- const char *args,
- void *opaque)
- {
- YADIFContext *yadif = ctx->priv;
- av_unused int cpu_flags = av_get_cpu_flags();
- yadif->mode = 0;
- yadif->parity = -1;
- yadif->csp = NULL;
- // 滤镜函数指针初始化赋值
- yadif->filter_line = filter_line_c;
- return 0;
- }
2. 接着来看两个filter的Pad连接时的媒体类型的协商机制
- int avfilter_graph_config(AVFilterGraph *graphctx, void *log_ctx)
- {
- int ret;
// 检查filter的权限
- if ((ret = ff_avfilter_graph_check_validity(graphctx, log_ctx)))
- return ret;
-
- // 检查Pad支持的媒体类型
- if ((ret = ff_avfilter_graph_config_formats(graphctx, log_ctx)))
- return ret;
//
- if ((ret = ff_avfilter_graph_config_links(graphctx, log_ctx)))
- return ret;
- return 0;
- }
检查Pad支持的媒体类型 :
- int ff_avfilter_graph_config_formats(AVFilterGraph *graph,
- AVClass *log_ctx)
- {
- int ret;
- /* find supported formats from sub-filters, and merge along links */
- if ((ret = query_formats(graph, log_ctx)) < 0)
- return ret;
- /* Once everything is merged, it's possible that we'll still have
- * multiple valid media format choices. We pick the first one. */
- pick_formats(graph);
- return 0;
- }
- static int query_formats(AVFilterGraph *graph,
- AVClass *log_ctx)
- {
- int i, j, ret;
- int scaler_count = 0;
- char inst_name[30];
- /* ask all the sub-filters for their supported media formats */
- for (i = 0; i < graph->filter_count; i++) {
- if (graph->filters[i]->filter->query_formats)
- graph->filters[i]->filter->query_formats(graph->filters[i]);
- else
- avfilter_default_query_formats(graph->filters[i]);
- }
- /* go through and merge as many format lists as possible */
- for (i = 0; i < graph->filter_count; i++) {
- …
-
- }
- return 0;
- }
- /* 检查连接用Pad支持的媒体类型 */
- static int query_formats(AVFilterContext *ctx)
- {
- static const enum PixelFormat pix_fmts[] = {
- PIX_FMT_YUV420P,
- PIX_FMT_YUV422P,
- PIX_FMT_YUV444P,
- PIX_FMT_YUV410P,
- PIX_FMT_YUV411P,
- PIX_FMT_GRAY8,
- PIX_FMT_YUVJ420P,
- PIX_FMT_YUVJ422P,
- PIX_FMT_YUVJ444P,
- AV_NE( PIX_FMT_GRAY16BE, PIX_FMT_GRAY16LE ),
- PIX_FMT_YUV440P,
- PIX_FMT_YUVJ440P,
- AV_NE( PIX_FMT_YUV420P16BE, PIX_FMT_YUV420P16LE ),
- AV_NE( PIX_FMT_YUV422P16BE, PIX_FMT_YUV422P16LE ),
- AV_NE( PIX_FMT_YUV444P16BE, PIX_FMT_YUV444P16LE ),
- PIX_FMT_NONE
- };
- avfilter_set_common_pixel_formats(ctx,
- avfilter_make_format_list(pix_fmts));
- return 0;
- }
3. 最后来看滤镜的连接和对每帧图像处理时的调用
- int output_packet(AVInputStream *ist, int ist_index,
- AVOutputStream **ost_table,
- int nb_ostreams,
- const AVPacket *pkt,
- int *errorflag)
- {
- /* decode the packet if needed */
- if (ist->decoding_needed) {
- 解码;
- #if CONFIG_AVFILTER
- if(ist->st->codec->codec_type == AVMEDIA_TYPE_VIDEO)
- if (start_time == 0 || ist->pts >= start_time) {
- for(i=0;i<nb_ostreams;i++) {
- ost = ost_table[i];
- if (ost->input_video_filter && ost->source_index == ist_index) {
- if (!picture.sample_aspect_ratio.num)
- picture.sample_aspect_ratio = ist->st->sample_aspect_ratio;
- picture.pts = ist->pts;
- av_vsrc_buffer_add_frame(ost->input_video_filter, &picture, AV_VSRC_BUF_FLAG_OVERWRITE);
- }
- }
- }
- #endif
- #if CONFIG_AVFILTER
- frame_available = ist->st->codec->codec_type
- != AVMEDIA_TYPE_VIDEO ||
- !ost->output_video_filter ||
- avfilter_poll_frame(ost->output_video_filter->inputs[0]);
- while (frame_available) {
- if (ist->st->codec->codec_type == AVMEDIA_TYPE_VIDEO &&
- ost->output_video_filter) {
- AVRational ist_pts_tb = ost->output_video_filter->inputs[0]->time_base;
- if (av_vsink_buffer_get_video_buffer_ref(ost->output_video_filter,
- &ost->picref, 0) < 0)
- goto cont;
- if (ost->picref) {
- AVRational tempVar = {1, AV_TIME_BASE};
- avfilter_fill_frame_from_video_buffer_ref(&picture, ost->picref);
- //ist->pts = av_rescale_q(ost->picref->pts, ist_pts_tb, AV_TIME_BASE_Q);
- ist->pts = av_rescale_q(ost->picref->pts, ist_pts_tb, tempVar);//modify by chenrui
- }
- }
- #endif
- 编码;
- return 0;
- fail_decode:
- return -1;
- }
- }
- }
先来看滤镜的连接:
- int av_vsrc_buffer_add_frame(AVFilterContext *buffer_src,
- const AVFrame *frame, int flags)
- {
- // 从帧列表中得到当前帧
- AVFilterBufferRef *picref =
- avfilter_get_video_buffer_ref_from_frame(frame,
- AV_PERM_WRITE);
- if (!picref)
- return AVERROR(ENOMEM);
- ret = av_vsrc_buffer_add_video_buffer_ref(buffer_src,
- picref, flags);
-
-
- picref->buf->data[0] = NULL;
- avfilter_unref_buffer(picref);
-
- return ret;
- }
-
-
- int av_vsrc_buffer_add_video_buffer_ref(AVFilterContext *buffer_filter,
- AVFilterBufferRef *picref, int flags)"
- {
-
- 智能插入相应的filter;
-
- c->picref = avfilter_get_video_buffer(outlink, AV_PERM_WRITE,
- picref->video->w, picref->video->h);
-
- av_image_copy(c->picref->data, c->picref->linesize,
- picref->data, picref->linesize,
- picref->format, picref->video->w, picref->video->h);
- avfilter_copy_buffer_ref_props(c->picref, picref);
-
- return 0;
- }
-
-
- AVFilterBufferRef *avfilter_get_video_buffer(AVFilterLink *link,
- int perms, int w, int h)
- {
- AVFilterBufferRef *ret = NULL;
-
- if (link->dstpad->get_video_buffer)
- ret = link->dstpad->get_video_buffer(link, perms, w, h);
-
- if (!ret)
- ret = avfilter_default_get_video_buffer(link, perms, w, h);
-
- if (ret)
- ret->type = AVMEDIA_TYPE_VIDEO;
-
- return ret;
- }
-
- AVFilterBufferRef *get_video_buffer(AVFilterLink *link, int perms,
- int w, int h)
- {
- AVFilterBufferRef *picref;
- int width = FFALIGN(w, 32);
- int height= FFALIGN(h+2, 32);
- int i;
-
- picref = avfilter_default_get_video_buffer(link, perms, width, height);
-
- picref->video->w = w;
- picref->video->h = h;
-
- for (i = 0; i < 3; i++)
- picref->data[i] += picref->linesize[i];
-
- return picref;
- }
最后来看图像处理函数的实现:
- int avfilter_poll_frame(AVFilterLink *link)
- {
- int i, min = INT_MAX;
- if (link->srcpad->poll_frame)
- return link->srcpad->poll_frame(link);
- for (i = 0; i < link->src->input_count; i++) {
- int val;
- if (!link->src->inputs[i])
- return -1;
- val = avfilter_poll_frame(link->src->inputs[i]);
- min = FFMIN(min, val);
- }
- return min;
- }
- int poll_frame(AVFilterLink *link)
- {
- YADIFContext *yadif = link->src->priv;
- int ret, val;
- if (yadif->frame_pending)
- return 1;
- val = avfilter_poll_frame(link->src->inputs[0]);
- if (val==1 && !yadif->next) {
- //FIXME change API to not requre this red tape
- if ((ret = avfilter_request_frame(link->src->inputs[0])) < 0)
- return ret;
- val = avfilter_poll_frame(link->src->inputs[0]);
- }
- assert(yadif->next || !val);
- return val * ((yadif->mode&1)+1);
- }
- int avfilter_request_frame(AVFilterLink *link)
- {
- if (link->srcpad->request_frame)
- return link->srcpad->request_frame(link);
- else if (link->src->inputs[0])
- return avfilter_request_frame(link->src->inputs[0]);
- else return -1;
- }
- static int request_frame(AVFilterLink *link)
- {
- BufferSourceContext *c = link->src->priv;
- if (!c->picref) {
- av_log(link->src, AV_LOG_WARNING,
- "request_frame() called with no available frame!\n");
- return AVERROR(EINVAL);
- }
// 图像处理函数的真正实现
- avfilter_start_frame(link, avfilter_ref_buffer(c->picref, ~0));
- avfilter_draw_slice(link, 0, link->h, 1);
- avfilter_end_frame(link);
-
- avfilter_unref_buffer(c->picref);
- c->picref = NULL;
- return 0;
- }
完结。