FFmpeg进阶: 截取视频生成gif动图
文章目录
-
- 1.封装视频滤镜
- 2.截取视频生成gif
- 3.gif优化
- 4.示例效果
现在互联网上很多人都通过表情包来表达自己的情绪，常用的表情包很多都是视频文件的一部分。这里就介绍一下如何通过ffmpeg截取视频生成gif动图。其实原理很简单，首先我们seek到视频对应的位置，然后读取数据帧修改帧的数据格式并输出到gif文件当中，读取完毕之后我们就得到了一个视频动图。具体的操作步骤如下:
1.封装视频滤镜
首先封装一下视频滤镜，方便对数据帧进行变换处理
//video_filter.h
#ifndef VIDEOBOX_VIDEO_FILTER_H
#define VIDEOBOX_VIDEO_FILTER_H
extern "C" {
#include //video_filter.cpp
#include "video_filter.h"
int VideoFilter::create(const char *filter_descr, VideoConfig *inConfig, VideoConfig *outConfig) {
this->description = filter_descr;
char args[512];
int ret = 0;
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();
enum AVPixelFormat pix_fmts[] = {outConfig->format, AV_PIX_FMT_NONE};
filter_graph = avfilter_graph_alloc();
if (!outputs || !inputs || !filter_graph) {
ret = AVERROR(ENOMEM);
goto end;
}
snprintf(args, sizeof(args),
"video_size=%dx%d:pix_fmt=%d:time_base=%d/%d:pixel_aspect=%d/%d",
inConfig->width, inConfig->height, inConfig->format,
inConfig->timebase.num, inConfig->timebase.den,
inConfig->pixel_aspect.num, inConfig->pixel_aspect.num);
ret = avfilter_graph_create_filter(&buffersrc_ctx, buffersrc, "in",
args, nullptr, filter_graph);
if (ret < 0) {
goto end;
}
ret = avfilter_graph_create_filter(&buffersink_ctx, buffersink, "out",
nullptr, nullptr, filter_graph);
if (ret < 0) {
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) {
goto end;
}
outputs->name = av_strdup("in");
outputs->filter_ctx = buffersrc_ctx;
outputs->pad_idx = 0;
outputs->next = nullptr;
inputs->name = av_strdup("out");
inputs->filter_ctx = buffersink_ctx;
inputs->pad_idx = 0;
inputs->next = nullptr;
if ((ret = avfilter_graph_parse_ptr(filter_graph, filter_descr,
&inputs, &outputs, nullptr)) < 0) {
goto end;
}
if ((ret = avfilter_graph_config(filter_graph, nullptr)) < 0) {
goto end;
}
end:
avfilter_inout_free(&inputs);
avfilter_inout_free(&outputs);
return ret;
}
int VideoFilter::create(const char *filter_descr, VideoConfig *inConfig1, VideoConfig *inConfig2, VideoConfig *outConfig) {
this->description = filter_descr;
char args1[512];
char args2[512];
int ret = 0;
const AVFilter *buffersrc1 = avfilter_get_by_name("buffer");
const AVFilter *buffersrc2 = avfilter_get_by_name("buffer");
const AVFilter *buffersink = avfilter_get_by_name("buffersink");
AVFilterInOut *outputs = avfilter_inout_alloc();
AVFilterInOut *inputs = avfilter_inout_alloc();
AVFilterInOut *full_output = avfilter_inout_alloc();
enum AVPixelFormat pix_fmts[] = { outConfig->format, AV_PIX_FMT_NONE };
filter_graph = avfilter_graph_alloc();
if (!outputs || !inputs || !filter_graph || !full_output) {
ret = AVERROR(ENOMEM);
goto end;
}
snprintf(args1, sizeof(args1),
"video_size=%dx%d:pix_fmt=%d:time_base=%d/%d:pixel_aspect=%d/%d",
inConfig1->width, inConfig1->height, inConfig1->format,
inConfig1->timebase.num, inConfig1->timebase.den,
inConfig1->pixel_aspect.num, inConfig1->pixel_aspect.num);
snprintf(args2, sizeof(args2),
"video_size=%dx%d:pix_fmt=%d:time_base=%d/%d:pixel_aspect=%d/%d",
inConfig2->width, inConfig2->height, inConfig2->format,
inConfig2->timebase.num, inConfig2->timebase.den,
inConfig2->pixel_aspect.num, inConfig2->pixel_aspect.num);
ret = avfilter_graph_create_filter(&buffersrc_ctx, buffersrc1, "in",
args1, nullptr, filter_graph);
if (ret < 0) {
goto end;
}
ret = avfilter_graph_create_filter(&buffersrc_ctx1, buffersrc2, "in1",
args2, nullptr, filter_graph);
if (ret < 0) {
goto end;
}
ret = avfilter_graph_create_filter(&buffersink_ctx, buffersink, "out",
nullptr, nullptr, filter_graph);
if (ret < 0) {
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) {
goto end;
}
outputs->name = av_strdup("in");
outputs->filter_ctx = buffersrc_ctx;
outputs->pad_idx = 0;
outputs->next = full_output;
full_output->name = av_strdup("in1");
full_output->pad_idx = 0;
full_output->filter_ctx = buffersrc_ctx1;
full_output->next = NULL;
inputs->name = av_strdup("out");
inputs->filter_ctx = buffersink_ctx;
inputs->pad_idx = 0;
inputs->next = nullptr;
if ((ret = avfilter_graph_parse_ptr(filter_graph, filter_descr,
&inputs, &outputs, nullptr)) < 0) {
goto end;
}
if ((ret = avfilter_graph_config(filter_graph, nullptr)) < 0) {
goto end;
}
end:
avfilter_inout_free(&inputs);
avfilter_inout_free(&outputs);
return ret;
}
int VideoFilter::filter(AVFrame *source, AVFrame *dest) {
int ret = av_buffersrc_add_frame_flags(buffersrc_ctx, source, AV_BUFFERSRC_FLAG_KEEP_REF);
if (ret < 0) {
return -1;
}
ret = av_buffersink_get_frame(buffersink_ctx, dest);
if (ret < 0) {
return -1;
}
return 0;
}
int VideoFilter::filter(AVFrame * source1, AVFrame * source2, AVFrame * dest)
{
int ret = av_buffersrc_add_frame_flags(buffersrc_ctx, source1, AV_BUFFERSRC_FLAG_KEEP_REF);
if (ret < 0) {
return -1;
}
ret = av_buffersrc_add_frame_flags(buffersrc_ctx1, source2, AV_BUFFERSRC_FLAG_KEEP_REF);
if (ret < 0) {
return -1;
}
ret = av_buffersink_get_frame(buffersink_ctx, dest);
if (ret < 0) {
return -1;
}
return 0;
}
int VideoFilter::addInput1(AVFrame * input)
{
return av_buffersrc_add_frame_flags(buffersrc_ctx, input, AV_BUFFERSRC_FLAG_KEEP_REF);
}
int VideoFilter::addInput2(AVFrame * input)
{
return av_buffersrc_add_frame_flags(buffersrc_ctx1, input, AV_BUFFERSRC_FLAG_KEEP_REF);
}
int VideoFilter::getFrame(AVFrame * result)
{
return av_buffersink_get_frame(buffersink_ctx, result);
}
void VideoFilter::dumpGraph() {
printf("%s:%s", description, avfilter_graph_dump(filter_graph, nullptr));
}
void VideoFilter::destroy() {
if (filter_graph)
avfilter_graph_free(&filter_graph);
}
2.截取视频生成gif
封装完毕视频滤镜之后，我们就可以读取视频的数据帧，修改数据结构输出gif动图了，对应的实现如下:
#pragma execution_character_set("utf-8")
#define _CRT_SECURE_NO_WARNINGS
#include 3.gif优化
由于原始视频的像素比较高，帧率也比较高，这样截取出来的gif可能比较大。对于gif尺寸比较大，优化策略主要包括以下三点:
1.缩短截取的时间长度
2.对图片尺寸进行缩放处理
3.通过抽帧来降低视频的帧率
抽帧可能降低动图的流畅度，需要提起注意。
4.示例效果