一.概述
一般来说，给视频添加滤镜有两种方式，一种是录制的时候添加滤镜，如基于Open GL的GPUImage。还有一种是编码的时候添加滤镜，如FFmpeg。本文将使用FFmpeg框架中的AVFilter给视频添加滤镜。
本文使用FFmpeg 4.2，Mac OS系统
二.初始化滤镜
1.获取滤镜处理源：获得源及滤镜处理的Sink滤镜，同时申请输入与输出的滤镜结构AVFilterInOut。
const AVFilter *buffersrc = avfilter_get_by_name("buffer");
const AVFilter *buffersink = avfilter_get_by_name("buffersink");
AVFilterInOut *outputs = avfilter_inout_alloc();
AVFilterInOut *inputs = avfilter_inout_alloc();
2.处理AVFilterGraph：存储AVFilter的in和out描述信息。
filter_graph = avfilter_graph_alloc();
3.创建AVFilterContext
snprintf(args, sizeof(args),
"video_size=%dx%d:pix_fmt=%d:time_base=%d/%d:pixel_aspect=%d/%d",
1280,720,AV_PIX_FMT_YUV420P,
1, 25,1,1);
ret = avfilter_graph_create_filter(&buffersrc_ctx, buffersrc, "in",
args, NULL, filter_graph);
if (ret < 0) {
printf("Cannot create buffer source\n");
return;
}
/* buffer video sink: to terminate the filter chain. */
buffersink_params = av_buffersink_params_alloc();
buffersink_params->pixel_fmts = pix_fmts;
ret = avfilter_graph_create_filter(&buffersink_ctx, buffersink, "out",
NULL, buffersink_params, filter_graph);
if (ret < 0) {
printf("ret == %s\n", av_err2str(ret));
return;
}
4.设置其他参数
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");
return;
}
5.建立滤镜解析器
NSString *desc = @"[in]geq=r='X/W*r(X,Y)':g='(1-X/W)*g(X,Y)':b='(H-Y)/H*b(X,Y)',drawtext=fontfile=/Library/Fonts/Arial Unicode.ttf:x=10:y=10:fontcolor=white:fontsize=40:text='版权为爱奇艺官方所有，请勿应用于商业活动。'[text];movie=[path]aqylog.imageset/aqylog.png[wm];[text][wm]overlay=W-w-40:H-h-40 ,scale=1280:720";
const char *filter_descr = [desc cStringUsingEncoding:NSUTF8StringEncoding];
/* 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, filter_descr,
&inputs, &outputs, NULL)) < 0){
printf("Error avfilter_graph_parse_ptr \n");
return;
}
if ((ret = avfilter_graph_config(filter_graph, NULL)) < 0){
printf("Error avfilter_graph_config \n");
return;
}
6.初始化一个用于添加滤镜后输出的AVFrame
frame_out = av_frame_alloc();
frame_out->width = pCodecContext->width;
frame_out->height = pCodecContext->height;
frame_out->format = pCodecContext->pix_fmt;
ret = av_frame_get_buffer(frame_out, 0);
if (ret < 0) {
printf("ret == %s\n", av_err2str(ret));
}
avfilter_inout_free(&inputs);
avfilter_inout_free(&outputs);
av_free(buffersink_params);
三.编码时添加滤镜
上文已经介绍如何生成原始的AVFrame，添加滤镜后生成新的AVFrame，送入编码器编码。
int ret;
if (kUseAVFilter) {
frame_out->pts = frameCount;
frame_out->width = 1280;
frame_out->height = 720;
frame_out->format = AV_PIX_FMT_YUV420P;
frame_out->linesize[0] = 1280;
frame_out->linesize[1] = 640;
frame_out->linesize[2] = 640;
ret = av_buffersrc_add_frame(buffersrc_ctx, pFrame);
if (ret < 0) {
printf("av_buffersrc_add_frame == %s\n", av_err2str(ret));
return;
}
ret = av_buffersink_get_frame(buffersink_ctx, frame_out);
if (ret) {
printf("av_buffersink_get_frame == %s\n", av_err2str(ret));
return;
}
ret = avcodec_send_frame(pCodecContext, frame_out);
}else{
ret = avcodec_send_frame(pCodecContext, pFrame);
}
四.滤镜的效果
选择滤镜在于上文的filter_descr设置，由3个滤镜组成：
1.geq滤镜：实现冷暖分割效果
geq=r='X/W*r(X,Y)':g='(1-X/W)*g(X,Y)':b='(H-Y)/H*b(X,Y)'
2.drawtext文字滤镜：在视频上添加文字，需要注意的是添加中文要选择支持中文的.ttf文件，否则会显示方框。
drawtext=fontfile=/Library/Fonts/Arial Unicode.ttf:x=10:y=10:fontcolor=white:fontsize=40:text='版权为爱奇艺官方所有，请勿应用于商业活动。'[text]
3.movie滤镜，添加图片logo，WH是视频的整体宽高，wh是图片的宽高。
movie=[path]aqylog.imageset/aqylog.png[wm];[text][wm]overlay=W-w-40:H-h-40
效果如下:
原图
添加滤镜效果图
FFmpeg视频滤镜目前大概有近200种，常用的有：
淡入淡出的fade滤镜，消除logo的delogo滤镜，增加亮度的brightness滤镜等等，具体详见官方文档。
