上一篇我们实现了平台解码avi并用SurfaceView播放。
http://blog.csdn.net/column/details/15511.html
本篇我们在此基础上实现滤镜，水印等功能。
我们将使用最新版：
最新版ffmpeg ffmpeg3.3
新版Android studio Android studio2.3
新版JNI编译方式 CMake
如果对C/C++/JNI知识不够了解。
可以先看这里：
C语言小结 ：http://blog.csdn.net/king1425/article/details/70256764 **
C++小结（一）** ： http://blog.csdn.net/king1425/article/details/70260091
JNI高阶知识总结 ： http://blog.csdn.net/king1425/article/details/71405131
对ffmpeg不熟的客官看这里：http://blog.csdn.net/king1425/article/details/70597642
先上两张效果图：
黑白：const char *filters_descr = “lutyuv=’u=128:v=128’”;
添加水印：const char *filters_descr = “movie=/storage/emulated/0/ws.jpg[wm];[in][wm]overlay=5:5[out]”;
在前面的几篇文章中我们已经学会了用ffmpeg对音视频进行编解码，下面我们就主要介绍一下libavfilter
ffmpeg的libavfilter是为音视频添加特效功能的。
libavfilter的关键函数如下所示：
avfilter_register_all()：注册所有AVFilter。
avfilter_graph_alloc()：为FilterGraph分配内存。
avfilter_graph_create_filter()：创建并向FilterGraph中添加一个Filter。
avfilter_graph_parse_ptr()：将一串通过字符串描述的Graph添加到FilterGraph中。
avfilter_graph_config()：检查FilterGraph的配置。
av_buffersrc_add_frame()：向FilterGraph中加入一个AVFrame。
av_buffersink_get_frame()：从FilterGraph中取出一个AVFrame。
今天我们的示例程序中提供了几种特效：
const char *filters_descr = "lutyuv='u=128:v=128'";
//const char *filters_descr = "hflip";
//const char *filters_descr = "hue='h=60:s=-3'";
//const char *filters_descr = "crop=2/3*in_w:2/3*in_h";
//const char *filters_descr = "drawbox=x=200:y=200:w=300:h=300:color=pink@0.5";
//const char *filters_descr = "movie=/storage/emulated/0/ws.jpg[wm];[in][wm]overlay=5:5[out]";
//const char *filters_descr="drawgrid=width=100:height=100:thickness=4:color=pink@0.9";
更多的特效使用，请到官网学习，http://www.ffmpeg.org/ffmpeg-filters.html
下面看代码实现：
在我们的MainActivity中初始化了一个SurfaceView，并定义一个native函数用于把Surface传到底层（底层把处理过的数据交给Surface传给上层显示）
SurfaceView surfaceView = (SurfaceView) findViewById(R.id.surface_view);
surfaceHolder = surfaceView.getHolder();
surfaceHolder.addCallback(this);
...
public native int play(Object surface);
surfaceCreated（）函数中实现play函数。
@Override
public void surfaceCreated(SurfaceHolder holder) {
new Thread(new Runnable() {
@Override
public void run() {
play(surfaceHolder.getSurface());
}
}).start();
}
那么重点就是JNI层的play()函数做了什么？
首先我们在上一篇play()函数的基础上添加libavfilter各种特效需要的头文件
//added by ws for AVfilter start
#include <libavfilter/avfiltergraph.h>
#include <libavfilter/buffersrc.h>
#include <libavfilter/buffersink.h>
//added by ws for AVfilter end
};
然后我们声明初始化一些必要的结构体。
//added by ws for AVfilter start
const char *filters_descr = "lutyuv='u=128:v=128'";
//const char *filters_descr = "hflip";
//const char *filters_descr = "hue='h=60:s=-3'";
//const char *filters_descr = "crop=2/3*in_w:2/3*in_h";
//const char *filters_descr = "drawbox=x=200:y=200:w=300:h=300:color=pink@0.5";
//const char *filters_descr = "movie=/storage/emulated/0/ws.jpg[wm];[in][wm]overlay=5:5[out]";
//const char *filters_descr="drawgrid=width=100:height=100:thickness=4:color=pink@0.9";
AVFilterContext *buffersink_ctx;
AVFilterContext *buffersrc_ctx;
AVFilterGraph *filter_graph;
//added by ws for AVfilter end
现在我们可以正式的初始化AVfilter 了，代码比较多，对着上面的AVfilter 关键函数看比较好
//added by ws for AVfilter start----------init AVfilter--------------------------ws
char args[512];
int ret;
AVFilter *buffersrc = avfilter_get_by_name("buffer");
AVFilter *buffersink = avfilter_get_by_name("buffersink");//新版的ffmpeg库必须为buffersink
AVFilterInOut *outputs = avfilter_inout_alloc();
AVFilterInOut *inputs = avfilter_inout_alloc();
enum AVPixelFormat pix_fmts[] = { AV_PIX_FMT_YUV420P, AV_PIX_FMT_NONE };
AVBufferSinkParams *buffersink_params;
filter_graph = avfilter_graph_alloc();
/* 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",
pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt,
pCodecCtx->time_base.num, pCodecCtx->time_base.den,
pCodecCtx->sample_aspect_ratio.num, pCodecCtx->sample_aspect_ratio.den);
ret = avfilter_graph_create_filter(&buffersrc_ctx, buffersrc, "in",
args, NULL, filter_graph);
if (ret < 0) {
LOGD("Cannot create buffer source\n");
return ret;
}
/* 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);
av_free(buffersink_params);
if (ret < 0) {
LOGD("Cannot create buffer sink\n");
return ret;
}
/* 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;
// avfilter_link(buffersrc_ctx, 0, buffersink_ctx, 0);
if ((ret = avfilter_graph_parse_ptr(filter_graph, filters_descr,
&inputs, &outputs, NULL)) < 0) {
LOGD("Cannot avfilter_graph_parse_ptr\n");
return ret;
}
if ((ret = avfilter_graph_config(filter_graph, NULL)) < 0) {
LOGD("Cannot avfilter_graph_config\n");
return ret;
}
//added by ws for AVfilter end------------init AVfilter------------------------------ws
初始化完成后，
我们把解码器解码出来的帧进行加工改造。
//added by ws for AVfilter start
pFrame->pts = av_frame_get_best_effort_timestamp(pFrame);
//* push the decoded frame into the filtergraph
if (av_buffersrc_add_frame(buffersrc_ctx, pFrame) < 0) {
LOGD("Could not av_buffersrc_add_frame");
break;
}
ret = av_buffersink_get_frame(buffersink_ctx, pFrame);
if (ret < 0) {
LOGD("Could not av_buffersink_get_frame");
break;
}
//added by ws for AVfilter end
改造后的帧就是已经加上特效了
记着最后释放内存：
avfilter_graph_free(&filter_graph); //added by ws for avfilter
到此我们今天的功能已经实现了。
建议大家结合着代码看，否则如盲人摸象这一篇可能助你理解libavfilter： libavfilter实践指南 ：http://blog.csdn.net/king1425/article/details/71215686
demo源码在这里：
ffmpeg实战教程（八）Android平台下AVfilter 实现水印，滤镜等特效功能 ：
http://blog.csdn.net/King1425/article/details/71609520
