FFMPEG中avfilter模块 调用流程

FFMPEG中avfilter模块 调用流程

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前言

视频拼接

一、avfilter的调用流程图

二、filter的初始化

./ffmpeg -buffer_size 1024000 -i udp://@224.1.1.3:20000  -i udp://@224.1.1.3:20000 -filter_complex "[0:v]crop=900:900:10:10,scale=1920:1080[v0];[1:v]crop=900:900:10:10,scale=1920:1080[v1];[v0][v1]hstack=2[out]" -pkt_size 1316  -map [out]  -f mpegts  udp://@239.255.255.250:54546

AVFilterLink对应是描述符（scare:90:90）

三、两个特殊的filter

• 1.buffer filter （处理前中的数据放到这里）
• 2 buffersink filter （滤镜处理完成后放到这里）

四、初始化filter的基本过程

• 1、 创建 graph， avfilter_graph_alloc()
• 2、buffer filter 和buffersink filter
• 3、 分析filter描述符，并构造AVFilterGraph
• 4、使构建好的AVFilterGraph生效

init_filter函数实现

/*
* 初始化过滤器 
*/
static int32_t init_filters(const char * filter_desc)
{
	int32_t ret = 0;

	
	const AVFilter * buffersrc = ::avfilter_get_by_name("buffer");
	const AVFilter*  buffersink = ::avfilter_get_by_name("buffersink");
	AVFilterInOut * inputs = ::avfilter_inout_alloc();
	AVFilterInOut*  outputs = ::avfilter_inout_alloc();
	if (!inputs)
	{
		printf("alloc inputs failed !!!\n");
		return -1;
	}
	if (!outputs)
	{
		printf("alloc outputs failed !!!\n");
		return -1;
	}
	
	char args[1024] = { 0 };
	AVRational time_base = g_fmt_ctx_ptr->streams[g_video_stream_index]->time_base;
	// video_size=wxh:pix_fmt=xx:time_base=xxx/xxxx:pixel_aspect=xxx/xx
	snprintf(args, 1024, "video_size=%dx%d:pix_fmt=%d:time_base=%d/%d:pixel_aspect=%d/%d",
		g_codec_ctx_ptr->width, g_codec_ctx_ptr->height, g_codec_ctx_ptr->pix_fmt, 
		time_base.num, time_base.den, 
		g_codec_ctx_ptr->sample_aspect_ratio.num, g_codec_ctx_ptr->sample_aspect_ratio.den);
	
	//
	g_graph = ::avfilter_graph_alloc();

	if (!g_graph)
	{
		printf("alloc graph failed !!!\n");
		return -1;
	}

	//解析描述符 filter_desc 
	// "[0:v]crop=900:900:10:10,scale=1920:1080[v0];[1:v]crop=900:900:10:10,scale=1920:1080[v1];[v0][v1]hstack=2[out]"
	// [a][b]overlay=xxxx[out]
	// 输入 buffer filter 创建
	// 构造input 和output
	// args : 查看参数 命令 : ./ffmpeg -h filter=buffer
	ret = ::avfilter_graph_create_filter(&g_buffer_ctx, buffersrc, "in", args, NULL/*buffer 用户数据*/, g_graph);
	if (ret < 0)
	{
		printf("in -->avfilter graph create filter failed !!!");
		return ret;
	}
	


	// args 参数查看: ./ffmpeg -h filter=buffersink
	//buffersink AVOptions :
	//pix_fmts               ..FV.......set the supported pixel formats
	enum AVPixelFormat pix_fmts[] = { AV_PIX_FMT_YUV420P, AV_PIX_FMT_GRAY8, AV_PIX_FMT_NONE };

	// 输出buffer sink filter 创建
	ret = ::avfilter_graph_create_filter(&g_buffersink_ctx, buffersink, "out", NULL, NULL/*buffer 用户数据*/, g_graph);
	if (ret < 0)
	{
		printf("buffer sink filter graph create filter failed !!!");
		return -1;
	}
	ret = av_opt_set_int_list((void *)g_buffersink_ctx, "pix_fmts", pix_fmts, AV_PIX_FMT_NONE, AV_OPT_SEARCH_CHILDREN);
	//比较奇怪
	// create out
	inputs->name = av_strdup("out");
	inputs->filter_ctx = g_buffer_ctx;
	inputs->pad_idx = 0;
	inputs->next = NULL;
	// outpus 构造
	// create in
	outputs->name = av_strdup("in");
	outputs->filter_ctx = g_buffersink_ctx;
	outputs->pad_idx = 0;
	outputs->next = NULL;


	//最重要步骤//
	// create filter and add graph for filter desciption 
	ret = ::avfilter_graph_parse_ptr(g_graph, filter_desc, &inputs, &outputs, NULL );


	//graph 生效
	ret = ::avfilter_graph_config(g_graph, NULL);
	if (ret < 0)
	{
		printf("filter graph config failed !!!\n");
		return ret;
	}

	 ::avfilter_inout_free(&inputs);
	 ::avfilter_inout_free(&outputs);
	 inputs = NULL;
	 outputs = NULL;
	return 0;
}

五、使用filter步骤

• 1、 获得解码后得原始数据 PCM/YUV
• 2、 将数据添加到buffer filter中
• 3、从buffersink 中读取处理好得数据
• 4、当所有数据处理完成后， 释放资源

六、滤镜处理

/*** 
*解码器视频帧 滤镜处理
*/
static int filter_video(AVFrame* frame, AVFrame*filter_frame)
{
	// 向filter buffer中添加视频帧
	int32_t ret = ::av_buffersrc_add_frame(g_buffer_ctx, frame);
	if (ret < 0)
	{
		printf("filter buffersrc add frame failed (%s)!!!\n", make_error_string(ret));
		return ret;
	}
	//获取buffersink 处理完成后得数据

	while (true)
	{
		ret = ::av_buffersink_get_frame(g_buffersink_ctx, filter_frame);
		if (ret < 0)
		{
			//有可能buuffersink还没有处理好数据 需要继续获取得啦 ~~~~
			if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
			{
				// 需要释放资源啦 ~~~~
				// av_frame_unref(filter_frame);
				break;
			}
			return ret;
		}

		// 直接写入文件中区
		do_frame(filter_frame);
		av_frame_unref(filter_frame);
	}
	av_frame_unref(filter_frame);
}

效果图

总结

filter的demo地址：https://github.com/chensongpoixs/cmp4_box_avi_flv/tree/master/filter