FFMPEG-AVFilter研究

FFMPEG中的libswscale是做像素转换的，但是对于一些复杂的操作，比如添加水印等，这个库就不行了，这时候就要说一下另外一个AVFilter。AVFilter完全可以替代libswscale的所有功能，也许有一天，ffmpeg也会这样去做。AVFilter虽然学起来有点复杂，但是为了学好FFMPEG，为了涨工资，我忍了。(*^__^*) 嘻嘻……

概念:

做个directshow的同学，对于这一块应该很了解了。

1.AVFilterGraph:和dshow中的filtergraph功能基本上一样，管理filter的，可以看成filter的一个容器。

2.AVFilter:就是一个filter啦。但是为什么叫做filter,其实就是一个过滤器，目标资源通过该过滤器总该发生一点变化是吧。。。。。

3.AVFilterLink:代表两个filter的关联媒介。

4.AVFilterPad:代表一个filter的输入输出口，就跟dshow中的pin差不多。只有输入pad的叫做source，只有输出pad的叫做sink。

下面是官方提供的一个例子：

/*
*modifier by tongli
*/
#define _XOPEN_SOURCE 600 
#include <stdio.h>
#include <windows.h>
#include "snprintf.h"
extern "C"
{
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavfilter/avfiltergraph.h>
#include <libavfilter/avcodec.h>
#include <libavfilter/buffersink.h>
#include <libavfilter/buffersrc.h>
#include <libavutil/opt.h>
}

const char *filter_descr = "scale=78:24";

static AVFormatContext *fmt_ctx;
static AVCodecContext *dec_ctx;
AVFilterContext *buffersink_ctx;
AVFilterContext *buffersrc_ctx;
AVFilterGraph *filter_graph;
static int video_stream_index = -1;
static int64_t last_pts = AV_NOPTS_VALUE;

static int open_input_file(const char *filename)
{
	int ret;
	AVCodec *dec;

	if ((ret = avformat_open_input(&fmt_ctx, filename, NULL, NULL)) < 0) {
		av_log(NULL, AV_LOG_ERROR, "Cannot open input file\n");
		return ret;
	}

	if ((ret = avformat_find_stream_info(fmt_ctx, NULL)) < 0) {
		av_log(NULL, AV_LOG_ERROR, "Cannot find stream information\n");
		return ret;
	}

	/* select the video stream */
	ret = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_VIDEO, -1, -1, &dec, 0);
	if (ret < 0) {
		av_log(NULL, AV_LOG_ERROR, "Cannot find a video stream in the input file\n");
		return ret;
	}
	video_stream_index = ret;
	dec_ctx = fmt_ctx->streams[video_stream_index]->codec;
	av_opt_set_int(dec_ctx, "refcounted_frames", 1, 0);

	/* init the video decoder */
	if ((ret = avcodec_open2(dec_ctx, dec, NULL)) < 0) {
		av_log(NULL, AV_LOG_ERROR, "Cannot open video decoder\n");
		return ret;
	}

	return 0;
}

static int init_filters(const char *filters_descr)
{
	char args[512];
	int ret = 0;
	AVFilter *buffersrc = avfilter_get_by_name("buffer");
	AVFilter *buffersink = avfilter_get_by_name("buffersink");
	AVFilterInOut *outputs = avfilter_inout_alloc();
	AVFilterInOut *inputs = avfilter_inout_alloc();
	AVRational time_base = fmt_ctx->streams[video_stream_index]->time_base;
	enum AVPixelFormat pix_fmts[] = { AV_PIX_FMT_GRAY8, AV_PIX_FMT_NONE };

	filter_graph = avfilter_graph_alloc();
	if (!outputs || !inputs || !filter_graph) {
		ret = AVERROR(ENOMEM);
		goto end;
	}

	/* buffer video source: the decoded frames from the decoder will be inserted here. */
	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,
		time_base.num, 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;
	}

	/* buffer video sink: to terminate the filter chain. */
	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_int_list(buffersink_ctx, "pix_fmts", pix_fmts,
		AV_PIX_FMT_NONE, AV_OPT_SEARCH_CHILDREN);
	if (ret < 0) {
		av_log(NULL, AV_LOG_ERROR, "Cannot set output pixel format\n");
		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 ((ret = avfilter_graph_parse_ptr(filter_graph, filters_descr,
		&inputs, &outputs, NULL)) < 0)
		goto end;

	if ((ret = avfilter_graph_config(filter_graph, NULL)) < 0)
		goto end;

end:
	avfilter_inout_free(&inputs);
	avfilter_inout_free(&outputs);

	return ret;
}

static void display_frame(const AVFrame *frame, AVRational time_base)
{
	int x, y;
	uint8_t *p0, *p;
	int64_t delay;
	AVRational ar_base_q = { 1, AV_TIME_BASE };
	if (frame->pts != AV_NOPTS_VALUE) {
		if (last_pts != AV_NOPTS_VALUE) {
			/* sleep roughly the right amount of time;
			* usleep is in microseconds, just like AV_TIME_BASE. */
			delay = av_rescale_q(frame->pts - last_pts,
				time_base, ar_base_q);
			if (delay > 0 && delay < 1000000)
				//usleep(delay);
				Sleep(delay);
		}
		last_pts = frame->pts;
	}

	/* Trivial ASCII grayscale display. */
	p0 = frame->data[0];
	puts("\033c");
	for (y = 0; y < frame->height; y++) {
		p = p0;
		for (x = 0; x < frame->width; x++)
			putchar(" .-+#"[*(p++) / 52]);
		putchar('\n');
		p0 += frame->linesize[0];
	}
	fflush(stdout);
}

int main(int argc, char **argv)
{
	int ret;
	AVPacket packet;
	AVFrame *frame = av_frame_alloc();
	AVFrame *filt_frame = av_frame_alloc();
	int got_frame;

	if (!frame || !filt_frame) {
		perror("Could not allocate frame");
		exit(1);
	}

	av_register_all();
	avfilter_register_all();

	if ((ret = open_input_file("style.ts")) < 0)
		goto end;
	if ((ret = init_filters(filter_descr)) < 0)
		goto end;

	/* read all packets */
	while (1) {
		if ((ret = av_read_frame(fmt_ctx, &packet)) < 0)
			break;

		if (packet.stream_index == video_stream_index) {
			got_frame = 0;
			ret = avcodec_decode_video2(dec_ctx, frame, &got_frame, &packet);
			if (ret < 0) {
				av_log(NULL, AV_LOG_ERROR, "Error decoding video\n");
				break;
			}

			if (got_frame) {
				frame->pts = av_frame_get_best_effort_timestamp(frame);

				/* push the decoded frame into the filtergraph */
				if (av_buffersrc_add_frame_flags(buffersrc_ctx, frame, AV_BUFFERSRC_FLAG_KEEP_REF) < 0) {
					av_log(NULL, AV_LOG_ERROR, "Error while feeding the filtergraph\n");
					break;
				}

				/* pull filtered frames from the filtergraph */
				while (1) {
					ret = av_buffersink_get_frame(buffersink_ctx, filt_frame);
					if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
						break;
					if (ret < 0)
						goto end;
					display_frame(filt_frame, buffersink_ctx->inputs[0]->time_base);
					av_frame_unref(filt_frame);
				}
				av_frame_unref(frame);
			}
		}
		av_free_packet(&packet);
	}
end:
	avfilter_graph_free(&filter_graph);
	avcodec_close(dec_ctx);
	avformat_close_input(&fmt_ctx);
	av_frame_free(&frame);
	av_frame_free(&filt_frame);

	if (ret < 0 && ret != AVERROR_EOF) {
		fprintf(stderr, "Error occurred: %s\n"); //av_err2str(ret));
		exit(1);
	}

	exit(0);
}

未完待续。。。。