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：
- /*=============================================================================
- # 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：
- 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) $(OUT_APP) core *.core *~ *yuv
运行结果如下：
- licaibiao@ubuntu:~/test/FFMPEG/filter$ 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：
- 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