Question

我已经从CDN下载了flv格式的视频（视频H264和音频AAC），并将它们重新下载到MP4格式。但视频受篇幅限制。所以我已经在几个部分下载了每个视频：从起点，点1，点2开始（通过在url中使用seek参数）。每个点的开始时间早于前一个点的结束使用av_read_frame我扫描了所有部分，发现相交的数据包不仅具有相同的大小和顺序，而且它们的dts / pts相互偏移恒定值。因此，要从第1点开始使用视频连续开始视频，我必须执行以下操作：
1.在输出文件中创建输出头 2.从开始视频中复制所有不相交的数据包 3.将从点1开始的视频中的所有非相交数据包复制为dts值，并将其移动为常数

如何使用libav（而非ffmpeg）完成所有这些操作？我读了How can libavformat be used without using other libav libraries。但是在libav中，由于avformat_alloc_output_context2中没有libav，因此无效。对于像我这样的新手来说，源avconv.c源也太复杂了，无法隔离与流复制操作相关的部分有人可以举例说明：
- 打开 input_file1 和 input_file2 （仅当程序与通用教程中的标准不同时才需要）
- 使用相同的容器格式和相同的视频和音频格式打开和写入 output_file 标题 - 将来自 input_file1 的数据包写入 output_file 直至数据包，例如pos == XXX
- 将 input_file2 的数据包写入 output_file 以常数值更改其dts（或任何需要的） - 写出正确的trailer

计算之前的dts中的时移。

Answer 1

好的，我找到了那段代码，但正如我在评论中所说的，由于某些原因它无效。如果你能解决它，请告诉我

/*
 * merge.c
 *
 *  Created on: Nov 17, 2012
 *      Author: arash
 */

/* merge multiple "IDENTICAL" video file into one file */

#include <stdio.h>

#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"

AVFormatContext *i_fmt_ctx;
AVStream *i_video_stream;

AVFormatContext *o_fmt_ctx;
AVStream *o_video_stream;


int main(int argc, char* argv[])
{
    if (argc < 3)
    {
        fprintf(stderr, "usage : %s <input> [<input>...] <output>\n", argv[0]);
        return -1;
    }

    avcodec_register_all();
    av_register_all();

    /* should set to NULL so that avformat_open_input() allocate a new one */
    i_fmt_ctx = NULL;
    if (avformat_open_input(&i_fmt_ctx, argv[1], NULL, NULL)!=0)
    {
        fprintf(stderr, "could not open input file\n");
        return -1;
    }

    if (av_find_stream_info(i_fmt_ctx)<0)
    {
        fprintf(stderr, "could not find stream info\n");
        return -1;
    }

    //av_dump_format(i_fmt_ctx, 0, argv[1], 0);

    /* find first video stream */
    for (unsigned i=0; i<i_fmt_ctx->nb_streams; i++)
        if (i_fmt_ctx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO)
        {
            i_video_stream = i_fmt_ctx->streams[i];
            break;
        }
    if (i_video_stream == NULL)
    {
        fprintf(stderr, "didn't find any video stream\n");
        return -1;
    }

    avformat_alloc_output_context2(&o_fmt_ctx, NULL, NULL, argv[argc-1]);

    /*
     * since all input files are supposed to be identical (framerate, dimension, color format, ...)
     * we can safely set output codec values from first input file
     */
    o_video_stream = av_new_stream(o_fmt_ctx, 0);
    {
        AVCodecContext *c;
        c = o_video_stream->codec;
        c->bit_rate = 400000;
        c->codec_id = i_video_stream->codec->codec_id;
        c->codec_type = i_video_stream->codec->codec_type;
        c->time_base.num = i_video_stream->time_base.num;
        c->time_base.den = i_video_stream->time_base.den;
        fprintf(stderr, "time_base.num = %d time_base.den = %d\n", c->time_base.num, c->time_base.den);
        c->width = i_video_stream->codec->width;
        c->height = i_video_stream->codec->height;
        c->pix_fmt = i_video_stream->codec->pix_fmt;
        printf("%d %d %d", c->width, c->height, c->pix_fmt);
        c->flags = i_video_stream->codec->flags;
        c->flags |= CODEC_FLAG_GLOBAL_HEADER;
        c->me_range = i_video_stream->codec->me_range;
        c->max_qdiff = i_video_stream->codec->max_qdiff;

        c->qmin = i_video_stream->codec->qmin;
        c->qmax = i_video_stream->codec->qmax;

        c->qcompress = i_video_stream->codec->qcompress;
    }

    avio_open(&o_fmt_ctx->pb, argv[argc-1], AVIO_FLAG_WRITE);

    /* yes! this is redundant */
    av_close_input_file(i_fmt_ctx);

    avformat_write_header(o_fmt_ctx, NULL);

    int last_pts = 0;
    int last_dts = 0;
    for (int i=1; i<argc-1; i++)
    {
        i_fmt_ctx = NULL;
        if (avformat_open_input(&i_fmt_ctx, argv[i], NULL, NULL)!=0)
        {
            fprintf(stderr, "could not open input file\n");
            return -1;
        }

        if (av_find_stream_info(i_fmt_ctx)<0)
        {
            fprintf(stderr, "could not find stream info\n");
            return -1;
        }
        av_dump_format(i_fmt_ctx, 0, argv[i], 0);

        /* we only use first video stream of each input file */
        i_video_stream = NULL;
        for (unsigned s=0; s<i_fmt_ctx->nb_streams; s++)
            if (i_fmt_ctx->streams[s]->codec->codec_type == AVMEDIA_TYPE_VIDEO)
            {
                i_video_stream = i_fmt_ctx->streams[s];
                break;
            }

        if (i_video_stream == NULL)
        {
            fprintf(stderr, "didn't find any video stream\n");
            return -1;
        }

        int64_t pts, dts;
        while (1)
        {
            AVPacket i_pkt;
            av_init_packet(&i_pkt);
            i_pkt.size = 0;
            i_pkt.data = NULL;
            if (av_read_frame(i_fmt_ctx, &i_pkt) <0 )
                break;
            /*
             * pts and dts should increase monotonically
             * pts should be >= dts
             */
            i_pkt.flags |= AV_PKT_FLAG_KEY;
            pts = i_pkt.pts;
            i_pkt.pts += last_pts;
            dts = i_pkt.dts;
            i_pkt.dts += last_dts;
            i_pkt.stream_index = 0;

            //printf("%lld %lld\n", i_pkt.pts, i_pkt.dts);
            static int num = 1;
            printf("frame %d\n", num++);
            av_interleaved_write_frame(o_fmt_ctx, &i_pkt);
            //av_free_packet(&i_pkt);
            //av_init_packet(&i_pkt);
        }
        last_dts += dts;
        last_pts += pts;

        av_close_input_file(i_fmt_ctx);
    }

    av_write_trailer(o_fmt_ctx);

    avcodec_close(o_fmt_ctx->streams[0]->codec);
    av_freep(&o_fmt_ctx->streams[0]->codec);
    av_freep(&o_fmt_ctx->streams[0]);

    avio_close(o_fmt_ctx->pb);
    av_free(o_fmt_ctx);

    return 0;
}

Answer 2

在av_new_stream（）

中

您应该添加以下代码：

c->extradata = i_video_stream->codec->extradata;
c->extradata_size = i_video_stream->codec->extradata_size;

Answer 3

我已经替换了已弃用的方法，并且还添加了ALiang的更正。它有效。

`/*
 * merge.c
 *
 *  Created on: Nov 17, 2012
 *  Author: arash
 *
 *  Modified on: April 5, 2018
 *  Editor: Chebotarev Michael
 */
/* merge multiple "IDENTICAL" video file into one file */
#include <stdio.h>
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
AVFormatContext *i_fmt_ctx;
AVStream *i_video_stream;
AVFormatContext *o_fmt_ctx;
AVStream *o_video_stream;

int main(int argc, char* argv[])
{
if (argc < 3)
{
    fprintf(stderr, "usage : %s <input> [<input>...] <output>\n", argv[0]);
    return -1;
}

avcodec_register_all();
av_register_all();

/* should set to NULL so that avformat_open_input() allocate a new one */
i_fmt_ctx = NULL;
if (avformat_open_input(&i_fmt_ctx, argv[1], NULL, NULL) != 0)
{
    fprintf(stderr, "could not open input file\n");
    return -1;
}

if (avformat_find_stream_info(i_fmt_ctx, NULL) < 0)
{
    fprintf(stderr, "could not find stream info\n");
    return -1;
}

//av_dump_format(i_fmt_ctx, 0, argv[1], 0);

/* find first video stream */
for (unsigned i = 0; i<i_fmt_ctx->nb_streams; i++)
    if (i_fmt_ctx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO)
    {
        i_video_stream = i_fmt_ctx->streams[i];
        break;
    }
if (i_video_stream == NULL)
{
    fprintf(stderr, "didn't find any video stream\n");
    return -1;
}

avformat_alloc_output_context2(&o_fmt_ctx, NULL, NULL, argv[argc - 1]);

/*
* since all input files are supposed to be identical (framerate, dimension, color format, ...)
* we can safely set output codec values from first input file
*/
o_video_stream = avformat_new_stream(o_fmt_ctx, 0);
{
    AVCodecContext *c;
    c = o_video_stream->codec;
    c->bit_rate = 400000;
    c->codec_id = i_video_stream->codec->codec_id;
    c->codec_type = i_video_stream->codec->codec_type;
    c->time_base.num = i_video_stream->time_base.num;
    c->time_base.den = i_video_stream->time_base.den;
    fprintf(stderr, "time_base.num = %d time_base.den = %d\n", c->time_base.num, c->time_base.den);
    c->width = i_video_stream->codec->width;
    c->height = i_video_stream->codec->height;
    c->pix_fmt = i_video_stream->codec->pix_fmt;
    printf("%d %d %d", c->width, c->height, c->pix_fmt);
    c->flags = i_video_stream->codec->flags;
    c->flags |= CODEC_FLAG_GLOBAL_HEADER;
    c->me_range = i_video_stream->codec->me_range;
    c->max_qdiff = i_video_stream->codec->max_qdiff;

    c->qmin = i_video_stream->codec->qmin;
    c->qmax = i_video_stream->codec->qmax;

    c->qcompress = i_video_stream->codec->qcompress;

    c->extradata = i_video_stream->codec->extradata;
    c->extradata_size = i_video_stream->codec->extradata_size;
}

avio_open(&o_fmt_ctx->pb, argv[argc - 1], AVIO_FLAG_WRITE);

/* yes! this is redundant */
avformat_close_input(&i_fmt_ctx);

avformat_write_header(o_fmt_ctx, NULL);

int last_pts = 0;
int last_dts = 0;
for (int i = 1; i<argc - 1; i++)
{
    i_fmt_ctx = NULL;
    if (avformat_open_input(&i_fmt_ctx, argv[i], NULL, NULL) != 0)
    {
        fprintf(stderr, "could not open input file\n");
        return -1;
    }

    if (avformat_find_stream_info(i_fmt_ctx, NULL) < 0)
    {
        fprintf(stderr, "could not find stream info\n");
        return -1;
    }
    av_dump_format(i_fmt_ctx, 0, argv[i], 0);

    /* we only use first video stream of each input file */
    i_video_stream = NULL;
    for (unsigned s = 0; s<i_fmt_ctx->nb_streams; s++)
        if (i_fmt_ctx->streams[s]->codec->codec_type == AVMEDIA_TYPE_VIDEO)
        {
            i_video_stream = i_fmt_ctx->streams[s];
            break;
        }

    if (i_video_stream == NULL)
    {
        fprintf(stderr, "didn't find any video stream\n");
        return -1;
    }

    int64_t pts, dts;
    while (1)
    {
        AVPacket i_pkt;
        av_init_packet(&i_pkt);
        i_pkt.size = 0;
        i_pkt.data = NULL;
        if (av_read_frame(i_fmt_ctx, &i_pkt) <0)
            break;
        /*
        * pts and dts should increase monotonically
        * pts should be >= dts
        */
        i_pkt.flags |= AV_PKT_FLAG_KEY;
        pts = i_pkt.pts;
        i_pkt.pts += last_pts;
        dts = i_pkt.dts;
        i_pkt.dts += last_dts;
        i_pkt.stream_index = 0;

        //printf("%lld %lld\n", i_pkt.pts, i_pkt.dts);
        static int num = 1;
        printf("frame %d\n", num++);
        av_interleaved_write_frame(o_fmt_ctx, &i_pkt);
        //av_free_packet(&i_pkt);
        //av_init_packet(&i_pkt);
    }
    last_dts += dts;
    last_pts += pts;

    avformat_close_input(&i_fmt_ctx);
}

av_write_trailer(o_fmt_ctx);

avcodec_close(o_fmt_ctx->streams[0]->codec);
av_freep(&o_fmt_ctx->streams[0]->codec);
av_freep(&o_fmt_ctx->streams[0]);

avio_close(o_fmt_ctx->pb);
av_free(o_fmt_ctx);

return 0;
}`

如何使用libavformat连接具有相同编解码器的2个视频文件（重新复用）？

3 个答案: