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_Hextern "C" {#include <libavcodec/avcodec.h>
#include <libavfilter/avfilter.h>
#include <libavfilter/buffersrc.h>
#include <libavfilter/buffersink.h>
#include <libavutil/channel_layout.h>
#include <libavutil/opt.h>
}//滤镜输入和输出对应的配置
struct VideoConfig {AVPixelFormat format;int width;int height;AVRational timebase{1, 30};AVRational pixel_aspect{1, 1};VideoConfig(AVPixelFormat format, int width, int height, AVRational timebase = {1, 30},AVRational pixel_aspect = {1, 1}) {this->format = format; //像素格式this->width = width;   //视频宽this->height = height; //视频高}
};class VideoFilter {protected:AVFilterContext *buffersink_ctx;AVFilterContext *buffersrc_ctx;AVFilterContext *buffersrc_ctx1;AVFilterGraph *filter_graph;const char *description = nullptr;
public:VideoFilter() = default;//构建对应的滤镜int create(const char *filter_descr, VideoConfig *inConfig, VideoConfig *outConfig);int create(const char *filter_descr, VideoConfig *inConfig1, VideoConfig *inConfig2, VideoConfig *outConfig);//获取滤镜的输入和输出int filter(AVFrame *source, AVFrame *dest);int filter(AVFrame* source1, AVFrame* source2, AVFrame*dest);//添加输入1int addInput1(AVFrame * input);//添加输入2int addInput2(AVFrame* input);//获取处理之后的结果int getFrame(AVFrame* result);void dumpGraph();void destroy();
};#endif

//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 <string>
#include <iostream>
#include <thread>
#include <memory>
#include <iostream>
#include <fstream>extern "C"
{#include "libavutil/opt.h"
#include <libavcodec/avcodec.h>
#include <libavfilter/avfilter.h>
#include <libavformat/avformat.h>
#include <libavformat/avio.h>
#include <libavutil/avutil.h>
#include <libswresample/swresample.h>
#include <libswscale/swscale.h>
#include <libavutil/frame.h>
#include <libavutil/time.h>
#include <libavfilter/buffersink.h>
#include <libavfilter/buffersrc.h>
#include <libavutil/imgutils.h>
}
#include "video_filter.h"//@1输入视频文件的地址
//@2输出gif文件的地址
//@3起始时间(s)
//@4结束时间(s)
int convert_video_to_gif(const char *output_filename, const char *input_filename, float from, float to)
{if (from < 0 || from >= to) {return -1;}AVFormatContext *inFmtCtx = nullptr;AVFormatContext *outFmtCtx = nullptr;AVCodecContext *videoCodecCtx = nullptr;AVCodecContext *gifCodecCtx = nullptr;int ret = 0;//打开输入文件ret = avformat_open_input(&inFmtCtx, input_filename, nullptr, nullptr);ret = avformat_find_stream_info(inFmtCtx, nullptr);ret = avformat_alloc_output_context2(&outFmtCtx, nullptr, nullptr, output_filename);int video_idx = 0;for (int i = 0; i < inFmtCtx->nb_streams; ++i) {if (inFmtCtx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {video_idx = i;AVStream *inVideoStream = inFmtCtx->streams[i];AVStream *outVideoStream = avformat_new_stream(outFmtCtx, nullptr);//创建输出流和对应的编码器av_dict_copy(&outVideoStream->metadata, inVideoStream->metadata, 0);const AVCodec *inCodec = avcodec_find_decoder(inVideoStream->codecpar->codec_id);videoCodecCtx = avcodec_alloc_context3(inCodec);ret = avcodec_parameters_to_context(videoCodecCtx, inVideoStream->codecpar);ret = avcodec_open2(videoCodecCtx, inCodec, nullptr);const AVCodec *codec = avcodec_find_encoder(AV_CODEC_ID_GIF);gifCodecCtx = avcodec_alloc_context3(codec);gifCodecCtx->codec_id = AV_CODEC_ID_GIF;gifCodecCtx->time_base = { 1, 30 };gifCodecCtx->bit_rate = 100000;gifCodecCtx->pix_fmt = AV_PIX_FMT_RGB8;gifCodecCtx->width = 600;gifCodecCtx->height = 400;ret = avcodec_open2(gifCodecCtx, codec, nullptr);ret = avcodec_parameters_from_context(outVideoStream->codecpar, gifCodecCtx);}}av_dict_copy(&outFmtCtx->metadata, inFmtCtx->metadata, 0);if (!(outFmtCtx->flags & AVFMT_NOFILE)) {ret = avio_open(&outFmtCtx->pb, output_filename, AVIO_FLAG_WRITE);}//写gif文件头ret = avformat_write_header(outFmtCtx, nullptr);int64_t first_pts = av_rescale_q_rnd((int64_t)from, AVRational{ 1,1 },inFmtCtx->streams[video_idx]->time_base,AV_ROUND_DOWN);av_seek_frame(inFmtCtx, video_idx, first_pts, AVSEEK_FLAG_BACKWARD);//通过滤镜缩放视频,修改图片像素格式VideoFilter *filter = nullptr;filter = new VideoFilter();char filter_descr[128];snprintf(filter_descr, sizeof(filter_descr), "scale=600:400,format=pix_fmts=%s",av_get_pix_fmt_name(gifCodecCtx->pix_fmt));VideoConfig in(videoCodecCtx->pix_fmt, videoCodecCtx->width, videoCodecCtx->height);VideoConfig out(gifCodecCtx->pix_fmt, gifCodecCtx->width, gifCodecCtx->height);filter->create(filter_descr, &in, &out);int gif_pts = 0;int index = 0;while (true) {AVPacket packet{ 0 };av_init_packet(&packet);ret = av_read_frame(inFmtCtx, &packet);if (ret < 0) {break;}if (av_compare_ts(packet.pts, inFmtCtx->streams[packet.stream_index]->time_base,(int64_t)(to * 10), AVRational{ 1, 10 }) >= 0) {break;}//读取数据帧并进行输出if (packet.stream_index == video_idx) {AVFrame *frame = av_frame_alloc();ret = avcodec_send_packet(videoCodecCtx, &packet);if (ret < 0) {continue;}ret = avcodec_receive_frame(videoCodecCtx, frame);if (ret < 0) {continue;}filter->filter(frame, frame);frame->pts = gif_pts++;ret = avcodec_send_frame(gifCodecCtx, frame);if (ret < 0) {continue;}av_frame_free(&frame);AVPacket gifPkt{ 0 };av_init_packet(&gifPkt);ret = avcodec_receive_packet(gifCodecCtx, &gifPkt);if (ret < 0){continue;}gifPkt.stream_index = 0;av_packet_rescale_ts(&gifPkt, gifCodecCtx->time_base,outFmtCtx->streams[0]->time_base);ret = av_interleaved_write_frame(outFmtCtx, &gifPkt);}}if (filter != nullptr) {filter->destroy();delete filter;}avformat_close_input(&inFmtCtx);avformat_free_context(inFmtCtx);avformat_free_context(outFmtCtx);return 0;
}int main(int argc, char* argv[])
{if (argc != 3){printf("usage:%1 input filepath %2 outputfilepath");return -1;}//输入视频文件地址,输出gif的地址std::string fileInput = std::string(argv[1]);std::string fileOutput = std::string(argv[2]);avformat_network_init();convert_video_to_gif(fileOutput.c_str(), fileInput.c_str(), 30, 40);
}

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

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