ffmpeg 视频的剪切

源资源来自教程，来自慕课网李超，本人仅仅是添加注释

#include <stdlib.h>
#include <libavutil/timestamp.h>
#include <libavformat/avformat.h>static void log_packet(const AVFormatContext *fmt_ctx, const AVPacket *pkt, const char *tag)
{AVRational *time_base = &fmt_ctx->streams[pkt->stream_index]->time_base;printf("%s: pts:%s pts_time:%s dts:%s dts_time:%s duration:%s duration_time:%s stream_index:%d\n",tag,av_ts2str(pkt->pts), av_ts2timestr(pkt->pts, time_base),av_ts2str(pkt->dts), av_ts2timestr(pkt->dts, time_base),av_ts2str(pkt->duration), av_ts2timestr(pkt->duration, time_base),pkt->stream_index);
}int cut_video(double from_seconds, double end_seconds, const char* in_filename, const char* out_filename) {AVOutputFormat *ofmt = NULL;AVFormatContext *ifmt_ctx = NULL, *ofmt_ctx = NULL;AVPacket pkt;int ret, i;av_register_all();if ((ret = avformat_open_input(&ifmt_ctx, in_filename, 0, 0)) < 0) {fprintf(stderr, "Could not open input file '%s'", in_filename);goto end;}if ((ret = avformat_find_stream_info(ifmt_ctx, 0)) < 0) {fprintf(stderr, "Failed to retrieve input stream information");goto end;}av_dump_format(ifmt_ctx, 0, in_filename, 0);//输出上下文avformat_alloc_output_context2(&ofmt_ctx, NULL, NULL, out_filename);if (!ofmt_ctx) {fprintf(stderr, "Could not create output context\n");ret = AVERROR_UNKNOWN;goto end;}ofmt = ofmt_ctx->oformat;for (i = 0; i < ifmt_ctx->nb_streams; i++) {AVStream *in_stream = ifmt_ctx->streams[i];AVStream *out_stream = avformat_new_stream(ofmt_ctx, in_stream->codec->codec);if (!out_stream) {fprintf(stderr, "Failed allocating output stream\n");ret = AVERROR_UNKNOWN;goto end;}//拷贝流信息ret = avcodec_copy_context(out_stream->codec, in_stream->codec);if (ret < 0) {fprintf(stderr, "Failed to copy context from input to output stream codec context\n");goto end;}out_stream->codec->codec_tag = 0;if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)out_stream->codec->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;}av_dump_format(ofmt_ctx, 0, out_filename, 1);if (!(ofmt->flags & AVFMT_NOFILE)) {ret = avio_open(&ofmt_ctx->pb, out_filename, AVIO_FLAG_WRITE);if (ret < 0) {fprintf(stderr, "Could not open output file '%s'", out_filename);goto end;}}//写多媒体信息头ret = avformat_write_header(ofmt_ctx, NULL);if (ret < 0) {fprintf(stderr, "Error occurred when opening output file\n");goto end;}//定位跳去到指定流位置 秒数*时间基=开始剪切的位置ret = av_seek_frame(ifmt_ctx, -1, from_seconds*AV_TIME_BASE, AVSEEK_FLAG_ANY);if (ret < 0) {fprintf(stderr, "Error seek\n");goto end;}int64_t *dts_start_from = malloc(sizeof(int64_t) * ifmt_ctx->nb_streams);memset(dts_start_from, 0, sizeof(int64_t) * ifmt_ctx->nb_streams);int64_t *pts_start_from = malloc(sizeof(int64_t) * ifmt_ctx->nb_streams);memset(pts_start_from, 0, sizeof(int64_t) * ifmt_ctx->nb_streams);while (1) {AVStream *in_stream, *out_stream;ret = av_read_frame(ifmt_ctx, &pkt);if (ret < 0)break;in_stream  = ifmt_ctx->streams[pkt.stream_index];out_stream = ofmt_ctx->streams[pkt.stream_index];log_packet(ifmt_ctx, &pkt, "in");//和结束位置比较if (av_q2d(in_stream->time_base) * pkt.pts > end_seconds) {av_free_packet(&pkt);break;}if (dts_start_from[pkt.stream_index] == 0) {dts_start_from[pkt.stream_index] = pkt.dts;printf("dts_start_from: %s\n", av_ts2str(dts_start_from[pkt.stream_index]));}if (pts_start_from[pkt.stream_index] == 0) {pts_start_from[pkt.stream_index] = pkt.pts;printf("pts_start_from: %s\n", av_ts2str(pts_start_from[pkt.stream_index]));}/* copy packet *///时间基转换  pts 就是每一帧数据的播放时间 pkt.pts = av_rescale_q_rnd(pkt.pts - pts_start_from[pkt.stream_index], in_stream->time_base, out_stream->time_base, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);pkt.dts = av_rescale_q_rnd(pkt.dts - dts_start_from[pkt.stream_index], in_stream->time_base, out_stream->time_base, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);if (pkt.pts < 0) {pkt.pts = 0;}if (pkt.dts < 0) {pkt.dts = 0;}pkt.duration = (int)av_rescale_q((int64_t)pkt.duration, in_stream->time_base, out_stream->time_base);pkt.pos = -1;log_packet(ofmt_ctx, &pkt, "out");printf("\n");ret = av_interleaved_write_frame(ofmt_ctx, &pkt);if (ret < 0) {fprintf(stderr, "Error muxing packet\n");break;}av_free_packet(&pkt);}free(dts_start_from);free(pts_start_from);av_write_trailer(ofmt_ctx);
end:avformat_close_input(&ifmt_ctx);/* close output */if (ofmt_ctx && !(ofmt->flags & AVFMT_NOFILE))avio_closep(&ofmt_ctx->pb);avformat_free_context(ofmt_ctx);if (ret < 0 && ret != AVERROR_EOF) {fprintf(stderr, "Error occurred: %s\n", av_err2str(ret));return 1;}return 0;
}int main(int argc, char *argv[]){if(argc < 5){fprintf(stderr, "Usage: \command startime, endtime, srcfile, outfile");return -1;}double startime = atoi(argv[1]);double endtime = atoi(argv[2]);cut_video(startime, endtime, argv[3], argv[4]);return 0;
}

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