本篇博客相比上一篇《 ffmpeg滤镜学习一，movie+overlay滤镜实现视频加水印、画中画》更深入一些，本次的实现，可以控制子画面出现的时间段、子画面播放时间等，这篇文章主要参考了大师兄悟空公众号下的文章《使用 FFmpeg 实现画中画效果(一)》，下面看一下具体实现：
首先提出5个问题：
-
子画面展示位置？
-
子画面从主画面的哪个时间点开始播放？
-
子画面从子画面的哪个时间点开始播放？
-
子画面是按照时间段显示还是一直显示？
-
如果子画面和主画面不等长怎么办？
要解决这5个问题，主要使用overlay滤镜，如下：
ffmpeg -h filter=overlay
....首先通过x、y参数可以解决子画面显示位置的问题。
shortest参数可以解决主画面、子画面时间不等的问题。
enable参数可以解决2、4两个问题，第三个问题需要使用一个新的滤镜setpts，主画面与子画面的视频偏移可以通过setpts滤镜设置，如下：
ffmpeg -h filter=setpts设置画布：
const char *filter_descr = "movie=out1.mp4[in2];[in2]setpts=PTS[out2];[0:v][out2]overlay=x=20:y=120:enable='between(t,2,15)':shortest=1";下代码吧：
/*
* 实现对现有视频增加水印，可以是图片、也可以是视频，若为视频，类似画中画
*/
#include "myffmpeg/util.h"
extern "C"
{
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavutil/opt.h>
#include <libavfilter/buffersink.h>
#include <libavfilter/buffersrc.h>
int open_input_file(AVFormatContext *fmt, AVCodecContext **codecctx, AVCodec *codec, const char *filename, int index)
{
int ret = 0;
char msg[500];
*codecctx = avcodec_alloc_context3(codec);
ret = avcodec_parameters_to_context(*codecctx, fmt->streams[index]->codecpar);
if (ret < 0)
{
sprintf(msg, "avcodec_parameters_to_context error,ret:%d\n", ret);
lp_log(msg);
return -1;
}
// open 解码器
ret = avcodec_open2(*codecctx, codec, NULL);
if (ret < 0)
{
sprintf(msg, "avcodec_open2 error,ret:%d\n", ret);
lp_log(msg);
return -2;
}
printf("pix:%d\n", (*codecctx)->pix_fmt);
return ret;
}
int init_filter(AVFilterContext **buffersrc_ctx, AVFilterContext **buffersink_ctx, AVFilterGraph **filter_graph, AVStream *stream, AVCodecContext *codecctx, const char *filter_desc)
{
int ret = -1;
char args[512];
char msg[500];
const AVFilter *buffersrc = avfilter_get_by_name("buffer");
const AVFilter *buffersink = avfilter_get_by_name("buffersink");
AVFilterInOut *input = avfilter_inout_alloc();
AVFilterInOut *output = avfilter_inout_alloc();
AVRational time_base = stream->time_base;
enum AVPixelFormat pix_fmts[] = {AV_PIX_FMT_YUV420P, AV_PIX_FMT_NONE};
if (!output || !input || !filter_graph)
{
ret = -1;
sprintf(msg, "avfilter_graph_alloc/avfilter_inout_alloc error,ret:%d\n", ret);
lp_log(msg);
goto end;
}
snprintf(args, sizeof(args), "video_size=%dx%d:pix_fmt=%d:time_base=%d/%d:pixel_aspect=%d/%d", codecctx->width, codecctx->height, codecctx->pix_fmt, stream->time_base.num, stream->time_base.den, codecctx->sample_aspect_ratio.num, codecctx->sample_aspect_ratio.den);
ret = avfilter_graph_create_filter(buffersrc_ctx, buffersrc, "in", args, NULL, *filter_graph);
if (ret < 0)
{
sprintf(msg, "avfilter_graph_create_filter buffersrc error,ret:%d\n", ret);
lp_log(msg);
goto end;
}
ret = avfilter_graph_create_filter(buffersink_ctx, buffersink, "out", NULL, NULL, *filter_graph);
if (ret < 0)
{
sprintf(msg, "avfilter_graph_create_filter buffersink error,ret:%d\n", ret);
lp_log(msg);
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)
{
sprintf(msg, "av_opt_set_int_list error,ret:%d\n", ret);
lp_log(msg);
goto end;
}
/*
* 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.
*/
output->name = av_strdup("in");
output->filter_ctx = *buffersrc_ctx;
output->pad_idx = 0;
output->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.
*/
input->name = av_strdup("out");
input->filter_ctx = *buffersink_ctx;
input->pad_idx = 0;
input->next = NULL;
if ((ret = avfilter_graph_parse_ptr(*filter_graph, filter_desc, &input, &output, NULL)) < 0)
{
sprintf(msg, "avfilter_graph_parse_ptr error,ret:%d\n", ret);
lp_log(msg);
goto end;
}
if ((ret = avfilter_graph_config(*filter_graph, NULL)) < 0)
{
sprintf(msg, "avfilter_graph_config error,ret:%d\n", ret);
lp_log(msg);
goto end;
}
end:
avfilter_inout_free(&input);
avfilter_inout_free(&output);
return ret;
}
int my_filter(const char *name)
{
int ret;
char msg[500];
// const char *filter_descr = "movie=my_logo.png[wm];[in][wm]overlay=10:10[out]";
// const char *filter_descr = "scale=640:360,transpose=cclock";
const char *filter_descr = "movie=out1.mp4[in2];[in2]setpts=PTS[out2];[in][out2]overlay=x=20:y=120:enable='between(t,2,15)':shortest=1";
AVFormatContext *pFormatCtx = NULL;
AVCodecContext *pCodecCtx;
AVFilterContext *buffersink_ctx;
AVFilterContext *buffersrc_ctx;
AVFilterGraph *filter_graph;
AVCodec *codec;
int video_stream_index = -1;
AVPacket packet;
AVFrame *pFrame;
AVFrame *pFrame_out;
filter_graph = avfilter_graph_alloc();
FILE *fp_yuv = fopen("test.yuv", "wb+");
ret = avformat_open_input(&pFormatCtx, name, NULL, NULL);
if (ret < 0)
{
sprintf(msg, "avformat_open_input error,ret:%d\n", ret);
lp_log(msg);
ret = -1;
goto end;
}
ret = avformat_find_stream_info(pFormatCtx, NULL);
if (ret < 0)
{
sprintf(msg, "avformat_find_stream_info error,ret:%d\n", ret);
lp_log(msg);
ret = -2;
goto end;
}
ret = av_find_best_stream(pFormatCtx, AVMEDIA_TYPE_VIDEO, -1, -1, &codec, 0);
if (ret < 0)
{
sprintf(msg, "av_find_best_stream error,ret:%d\n", ret);
lp_log(msg);
ret = -3;
goto end;
}
// 获取到视频流索引
video_stream_index = ret;
av_dump_format(pFormatCtx, 0, name, 0);
if ((ret = open_input_file(pFormatCtx, &pCodecCtx, codec, name, video_stream_index)) < 0)
{
ret = -4;
sprintf(msg, "open_input_file error,ret:%d\n", ret);
lp_log(msg);
goto end;
}
if ((ret = init_filter(&buffersrc_ctx, &buffersink_ctx, &filter_graph, pFormatCtx->streams[video_stream_index], pCodecCtx, filter_descr)) < 0)
{
ret = -5;
sprintf(msg, "init_filter error,ret:%d\n", ret);
lp_log(msg);
goto end;
}
pFrame = av_frame_alloc();
pFrame_out = av_frame_alloc();
while (1)
{
if ((ret = av_read_frame(pFormatCtx, &packet)) < 0)
break;
if (packet.stream_index == video_stream_index)
{
ret = avcodec_send_packet(pCodecCtx, &packet);
if (ret < 0)
{
sprintf(msg, "avcodec_send_packet error,ret:%d\n", ret);
lp_log(msg);
break;
}
while (ret >= 0)
{
ret = avcodec_receive_frame(pCodecCtx, pFrame);
if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
{
break;
}
else if (ret < 0)
{
sprintf(msg, "avcodec_receive_frame error,ret:%d\n", ret);
lp_log(msg);
goto end;
}
pFrame->pts = pFrame->best_effort_timestamp;
/* push the decoded frame into the filtergraph */
ret = av_buffersrc_add_frame_flags(buffersrc_ctx, pFrame, AV_BUFFERSRC_FLAG_KEEP_REF);
if (ret < 0)
{
sprintf(msg, "av_buffersrc_add_frame_flags error,ret:%d\n", ret);
lp_log(msg);
break;
}
/* pull filtered frames from the filtergraph */
while (1)
{
ret = av_buffersink_get_frame(buffersink_ctx, pFrame_out);
if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
break;
if (ret < 0)
{
ret = -6;
goto end;
}
if (pFrame_out->format == AV_PIX_FMT_YUV420P)
{
//Y, U, V
for (int i = 0; i < pFrame_out->height; i++)
{
fwrite(pFrame_out->data[0] + pFrame_out->linesize[0] * i, 1, pFrame_out->width, fp_yuv);
}
for (int i = 0; i < pFrame_out->height / 2; i++)
{
fwrite(pFrame_out->data[1] + pFrame_out->linesize[1] * i, 1, pFrame_out->width / 2, fp_yuv);
}
for (int i = 0; i < pFrame_out->height / 2; i++)
{
fwrite(pFrame_out->data[2] + pFrame_out->linesize[2] * i, 1, pFrame_out->width / 2, fp_yuv);
}
}
av_frame_unref(pFrame_out);
}
av_frame_unref(pFrame);
}
}
av_packet_unref(&packet);
}
end:
avcodec_free_context(&pCodecCtx);
fclose(fp_yuv);
}
}