FFMPEG 最简滤镜filter使用实例（实现视频缩放，裁剪，水印等）

FFMPEG官网给出了FFMPEG 滤镜使用的实例，它是将视频中的像素点替换成字符，然后从终端输出。我在该实例的基础上稍微的做了修改，使它能够保存滤镜处理过后的文件。在上代码之前先明白几个概念：

Filter:代表单个filter
FilterPad:代表一个filter的输入或输出端口，每个filter都可以有多个输入和多个输出，只有输出pad的filter称为source,只有输入pad的filter称为sink
FilterLink：若一个filter的输出pad和另一个filter的输入pad名字相同，即认为两个filter之间建立了link
FilterChain:代表一串相互连接的filters，除了source和sink外，要求每个filter的输入输出pad都有对应的输出和输入pad

经典示例：



图中的一系列操作共使用了四个filter，分别是
splite：将输入的流进行分裂复制，分两路输出。
crop：根据给定的参数，对视频进行裁剪
vflip：根据给定参数，对视频进行翻转等操作
overlay：将一路输入覆盖到另一路之上，合并输出为一路视频

下面上代码：

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/*=============================================================================

# FileName: filter_video.c

# Desc: an example of ffmpeg fileter

# Author: licaibiao

# LastChange: 2017-03-16

=============================================================================*/

#define _XOPEN_SOURCE 600 /* for usleep */

#include <unistd.h>

#include "avcodec.h"

#include "avformat.h"

#include "avfiltergraph.h"

#include "avcodec.h"

#include "buffersink.h"

#include "buffersrc.h"

#include "opt.h"

#define SAVE_FILE

const charchar *filter_descr = "scale=iw*2:ih*2";

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 charchar *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 判断流是否正常 */

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); /* refcounted_frames 帧引用计数 */

/* 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 charchar *filters_descr)

{

char args[512];

int ret = 0;

AVFilter *buffersrc = avfilter_get_by_name("buffer"); /* 输入buffer filter */

AVFilter *buffersink = avfilter_get_by_name("buffersink"); /* 输出buffer filter */

AVFilterInOut *outputs = avfilter_inout_alloc();

AVFilterInOut *inputs = avfilter_inout_alloc();

AVRational time_base = fmt_ctx->streams[video_stream_index]->time_base; /* 时间基数 */

#ifndef SAVE_FILE

enum AVPixelFormat pix_fmts[] = { AV_PIX_FMT_GRAY8, AV_PIX_FMT_NONE };

#else

enum AVPixelFormat pix_fmts[] = { AV_PIX_FMT_YUV420P, AV_PIX_FMT_NONE };

#endif

filter_graph = avfilter_graph_alloc(); /* 创建graph */

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);

/* 创建并向FilterGraph中添加一个Filter */

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;

}

/* Set a binary option to an integer list. */

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;

}

/*

* Set the endpoints for the filter graph. The filter_graph will

* be linked to the graph described by filters_descr.

*/

/*

* The buffer source output must be connected to the input pad of

* the first filter described by filters_descr; since the first

* filter input label is not specified, it is set to "in" by

* default.

*/

outputs->name = av_strdup("in");

outputs->filter_ctx = buffersrc_ctx;

outputs->pad_idx = 0;

outputs->next = NULL;

/*

* The buffer sink input must be connected to the output pad of

* the last filter described by filters_descr; since the last

* filter output label is not specified, it is set to "out" by

* default.

*/

inputs->name = av_strdup("out");

inputs->filter_ctx = buffersink_ctx;

inputs->pad_idx = 0;

inputs->next = NULL;

/* Add a graph described by a string to a graph */

if ((ret = avfilter_graph_parse_ptr(filter_graph, filters_descr,

&inputs, &outputs, NULL)) < 0)

goto end;

/* Check validity and configure all the links and formats in the graph */

if ((ret = avfilter_graph_config(filter_graph, NULL)) < 0)

goto end;

end:

avfilter_inout_free(&inputs);

avfilter_inout_free(&outputs);

return ret;

}

#ifndef SAVE_FILE

static void display_frame(const AVFrame *frame, AVRational time_base)

{

int x, y;

uint8_t *p0, *p;

int64_t delay;

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. */

/* 计算 pts 是用来把时间戳从一个时基调整到另外一个时基时候用的函数 */

delay = av_rescale_q(frame->pts - last_pts,

time_base, AV_TIME_BASE_Q);

if (delay > 0 && delay < 1000000)

usleep(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);

}

#else

FILEFILE * file_fd;

static void write_frame(const AVFrame *frame)

{

static int printf_flag = 0;

if(!printf_flag){

printf_flag = 1;

printf("frame widht=%d,frame height=%d\n",frame->width,frame->height);

if(frame->format==AV_PIX_FMT_YUV420P){

printf("format is yuv420p\n");

}

else{

printf("formet is = %d \n",frame->format);

}

}

fwrite(frame->data[0],1,frame->width*frame->height,file_fd);

fwrite(frame->data[1],1,frame->width/2*frame->height/2,file_fd);

fwrite(frame->data[2],1,frame->width/2*frame->height/2,file_fd);

}

#endif

int main(int argc, charchar **argv)

{

int ret;

AVPacket packet;

AVFrame *frame = av_frame_alloc();

AVFrame *filt_frame = av_frame_alloc();

int got_frame;

#ifdef SAVE_FILE

file_fd = fopen("test.yuv","wb+");

#endif

if (!frame || !filt_frame) {

perror("Could not allocate frame");

exit(1);

}

if (argc != 2) {

fprintf(stderr, "Usage: %s file\n", argv[0]);

exit(1);

}

av_register_all();

avfilter_register_all();

if ((ret = open_input_file(argv[1])) < 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); /* pts: Presentation Time Stamp */

/* 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;

#ifndef SAVE_FILE

display_frame(filt_frame, buffersink_ctx->inputs[0]->time_base);

#else

write_frame(filt_frame);

#endif

av_frame_unref(filt_frame);

}

/* Unreference all the buffers referenced by frame and reset the frame fields. */

av_frame_unref(frame);

}

}

av_packet_unref(&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);

}

#ifdef SAVE_FILE

fclose(file_fd);

#endif

exit(0);

}

该工程中，我的Makefile文件如下：

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OUT_APP = test

INCLUDE_PATH = /usr/local/include/

INCLUDE = -I$(INCLUDE_PATH)libavutil/ -I$(INCLUDE_PATH)libavdevice/ \

-I$(INCLUDE_PATH)libavcodec/ -I$(INCLUDE_PATH)libswresample \

-I$(INCLUDE_PATH)libavfilter/ -I$(INCLUDE_PATH)libavformat \

-I$(INCLUDE_PATH)libswscale/

FFMPEG_LIBS = -lavformat -lavutil -lavdevice -lavcodec -lswresample -lavfilter -lswscale

SDL_LIBS =

LIBS = $(FFMPEG_LIBS)$(SDL_LIBS)

COMPILE_OPTS = $(INCLUDE)

C = c

OBJ = o

C_COMPILER = cc

C_FLAGS = $(COMPILE_OPTS) $(CPPFLAGS) $(CFLAGS)

LINK = cc -o

LINK_OPTS = -lz -lm -lpthread

LINK_OBJ = test.o

.$(C).$(OBJ):

$(C_COMPILER) -c $(C_FLAGS) $<

$(OUT_APP): $(LINK_OBJ)

$(LINK)$@ $(LINK_OBJ) $(LIBS) $(LINK_OPTS)

clean:

-rm -rf *.$(OBJ) $(OUT_APP) core *.core *~ *yuv

运行结果如下：

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licaibiao@ubuntu:~/test/FFMPEG/filter$ ls

Makefile school.flv test test.c test.o

licaibiao@ubuntu:~/test/FFMPEG/filter$ ./test school.flv

[flv @ 0x12c16c0] video stream discovered after head already parsed

[flv @ 0x12c16c0] audio stream discovered after head already parsed

frame widht=1024,frame height=576

format is yuv420p

licaibiao@ubuntu:~/test/FFMPEG/filter$ ls

Makefile school.flv test test.c test.o test.yuv

在这里，我打印出来了输出视频的格式和图片的长和宽，该实例生成的是一个YUV420 格式的视频，使用YUV播放器播放视频的时候，需要设置正确的视频长度和宽度。在代码中通过设置enum AVPixelFormat pix_fmts[] = { AV_PIX_FMT_YUV420P, AV_PIX_FMT_NONE };来设置输出格式。

过滤器的参数设置是通过const char *filter_descr = "scale=iw*2:ih*2"; 来设置。它表示将视频的长和框都拉伸到原来的两倍。具体的filter参数可以通过命令：ffmpeg -filters 来查询。结果如下：

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Filters:

T.. = Timeline support

.S. = Slice threading

..C = Command support

A = Audio input/output

V = Video input/output

N = Dynamic number and/or type of input/output

| = Source or sink filter

... abench A->A Benchmark part of a filtergraph.

... acompressor A->A Audio compressor.

... acrossfade AA->A Cross fade two input audio streams.

... acrusher A->A Reduce audio bit resolution.

.............................................................................

在上面的代码中，我们设置的是将图片拉升到原来图像的两倍，其显示效果如下，可能是截图的问题，这里看好像没有拉伸到两倍。



原图



拉伸后

在上面的代码中，我们设置的是：

const char *filter_descr = "scale=iw*2:ih*2"; iw 表示输入视频的宽，ih表示输入视频的高。可以任意比例的缩放视频。这里*2 表示放大两倍,如果是/2表示缩小两倍。

视频缩放还可以直接设置：

const char *filter_descr = "scale=320:240"; 设置视频输出宽为320，高位240，当然也是可以随意的设置其他的参数。

视频的裁剪可以设置为：

const char *filter_descr = "crop=320:240:0:0"; 具体含义是 crop=width:height:x:y，其中 width 和 height 表示裁剪后的尺寸，x:y 表示裁剪区域的左上角坐标。

视频添加一个网格水印可以设置为：

const char *filter_descr = "drawgrid=width=100:height=100:thickness=2:color=red@0.5"; 具体含义是 width 和 height 表示添加网格的宽和高，thickness表示网格的线宽，color表示颜色 。其效果如下：



更多filter参数的使用，可以直接参考ffmpeg 的官方文档：http://www.ffmpeg.org/ffmpeg-filters.html