如何使用FFmpeg C API剪切视频？例如从00:10:00到00:20:00。 我需要使用哪些功能？
我使用此功能转换视频：
int convert(char *file) {
AVFrame *frame;
AVPacket inPacket, outPacket;
if(avio_open(&outFormatContext->pb, file, AVIO_FLAG_WRITE) < 0) {
fprintf(stderr, "convert(): cannot open out file\n");
return 0;
}
avformat_write_header(outFormatContext, NULL);
frame = avcodec_alloc_frame();
av_init_packet(&inPacket);
while(av_read_frame(inFormatContext, &inPacket) >= 0) {
if(inPacket.stream_index == inVideoStreamIndex) {
avcodec_decode_video2(inCodecContext, frame, &frameFinished, &inPacket);
if(frameFinished) {
av_init_packet(&outPacket);
avcodec_encode_video2(outCodecContext, &outPacket, frame, &outputed);
if(outputed) {
if (av_write_frame(outFormatContext, &outPacket) != 0) {
fprintf(stderr, "convert(): error while writing video frame\n");
return 0;
}
}
av_free_packet(&outPacket);
}
}
}
av_write_trailer(outFormatContext);
av_free_packet(&inPacket);
return 1;
}
答案 0 :(得分：7)
如果您只想剪切视频，则无需根据需要重新编码视频。 所以我想你出于某种原因想要剪切和重新编码。所以，基于您的代码：
观察您必须有权访问视频AVStream*结构...我将其命名为inVideoStream。
int convert_and_cut(char *file, float starttime, float endtime) {
AVFrame *frame;
AVPacket inPacket, outPacket;
if(avio_open(&outFormatContext->pb, file, AVIO_FLAG_WRITE) < 0) {
fprintf(stderr, "convert(): cannot open out file\n");
return 0;
}
// seek to the start time you wish.
// BEGIN
AVRational default_timebase;
default_timebase.num = 1;
default_timebase.den = AV_TIME_BASE;
// suppose you have access to the "inVideoStream" of course
int64_t starttime_int64 = av_rescale_q((int64_t)( starttime * AV_TIME_BASE ), default_timebase, inVideoStream->time_base);
int64_t endtime_int64 = av_rescale_q((int64_t)( endtime * AV_TIME_BASE ), default_timebase, inVideoStream->time_base);
if(avformat_seek_file(inFormatContext, inVideoStreamIndex, INT64_MIN, starttime_int64, INT64_MAX, 0) < 0) {
// error... do something...
return 0; // usually 0 is used for success in C, but I am following your code.
}
avcodec_flush_buffers( inVideoStream->codec );
// END
avformat_write_header(outFormatContext, NULL);
frame = avcodec_alloc_frame();
av_init_packet(&inPacket);
// you used avformat_seek_file() to seek CLOSE to the point you want... in order to give precision to your seek,
// just go on reading the packets and checking the packets PTS (presentation timestamp)
while(av_read_frame(inFormatContext, &inPacket) >= 0) {
if(inPacket.stream_index == inVideoStreamIndex) {
avcodec_decode_video2(inCodecContext, frame, &frameFinished, &inPacket);
// this line guarantees you are getting what you really want.
if(frameFinished && frame->pkt_pts >= starttime_int64 && frame->pkt_pts <= endtime_int64) {
av_init_packet(&outPacket);
avcodec_encode_video2(outCodecContext, &outPacket, frame, &outputed);
if(outputed) {
if (av_write_frame(outFormatContext, &outPacket) != 0) {
fprintf(stderr, "convert(): error while writing video frame\n");
return 0;
}
}
av_free_packet(&outPacket);
}
// exit the loop if you got the frames you want.
if(frame->pkt_pts > endtime_int64) {
break;
}
}
}
av_write_trailer(outFormatContext);
av_free_packet(&inPacket);
return 1;
}
答案 1 :(得分：6)
正如Wagner Patriota所说，“如果你只想剪切视频，如果你愿意，你不需要重新编码视频”。以下是基于ffmpeg remuxing.c示例的代码，您无需重新编码视频。
#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);
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;
}
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;
}
}
ret = avformat_write_header(ofmt_ctx, NULL);
if (ret < 0) {
fprintf(stderr, "Error occurred when opening output file\n");
goto end;
}
// int indexs[8] = {0};
// int64_t start_from = 8*AV_TIME_BASE;
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");
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 */
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;
}
答案 2 :(得分：0)
另外，正如ustin所说，代码基于ffmpeg remuxing.c示例。
在out_stream->time_base = in_stream->time_base;前添加out_stream->codec->codec_tag = 0;
在int64_t *start_from = NULL;之后添加int stream_mapping_size = 0;
在start_from = av_mallocz_array(stream_mapping_size, sizeof(*start_from));之后添加stream_mapping = av_mallocz_array(stream_mapping_size, sizeof(*stream_mapping));
在start_from[stream_mapping[i]] = INT16_MIN;之后添加stream_mapping[i] = stream_index++;
添加
if (start_from[pkt.stream_index] == INT16_MIN) {
int64_t dts = pkt.dts;
int64_t pts = pkt.pts;
int64_t min_ts = dts > pts ? pts : dts;
start_from[pkt.stream_index] = min_ts < 0 ? 0 : min_ts;
}
之后
if (pkt.stream_index >= stream_mapping_size ||
stream_mapping[pkt.stream_index] < 0) {
av_packet_unref(&pkt);
continue;
}
pkt.pts = av_rescale_q_rnd(pkt.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 - start_from[pkt.stream_index], in_stream->time_base, out_stream->time_base, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);
free(start_from);之前添加end:提示：开始/结束时间戳就像贾斯汀说的