小贝子编程

如何使用libavformat来连接2个具有相同编解码器的视频文件(重新混合)



我从CDN下载了flv格式的视频(视频H264和音频AAC)，并将其重制为MP4格式。但视频受长度限制。所以我下载了几个部分的每个视频:开始在起点，在点1，在点2(通过使用url中的seek参数)。每个点的开始都比前一个点的结束要早一点。
使用av_read_frame对所有部分进行扫描，发现相交的数据包不仅大小和顺序相同，而且它们的dts/pts彼此以恒定值移动。因此，要将起始视频与从点1开始的视频连接起来，我必须这样做:
1. 在输出文件
中创建输出头2. 从起始视频复制所有不相交的数据包。
3.复制从第1点开始的视频中所有不相交的数据包，改变dts值，通过常量

如何使用libav(不是ffmpeg)做所有这些?我读了如何在不使用其他libav库的情况下使用libavformat。但在libav中它不起作用，因为libav中没有avformat_alloc_output_context2。另外，avconv.c源码对于像我这样的新手来说太复杂了，无法隔离与流复制操作相关的部分。
谁能给我举个例子:
-打开input_file1和input_file2(仅当程序与通用教程中的标准不同时需要)
-打开和写入头output_file相同的容器格式和相同的视频和音频格式
-将input_file1到output_file的数据包写入pos == XXX
-写入数据包从input_file2到output_file更改其dts(或任何需要的值)
-写正确的trailer

计算dts的时移之前做过

好的，我发现了这段代码，但正如我在评论中所说的，由于某种原因它不起作用。如果你能修好它，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 filen");
        return -1;
    }
    if (av_find_stream_info(i_fmt_ctx)<0)
    {
        fprintf(stderr, "could not find stream infon");
        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 streamn");
        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 = %dn", 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 filen");
            return -1;
        }
        if (av_find_stream_info(i_fmt_ctx)<0)
        {
            fprintf(stderr, "could not find stream infon");
            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 streamn");
            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 %lldn", i_pkt.pts, i_pkt.dts);
            static int num = 1;
            printf("frame %dn", 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;
}

我已经替换了不推荐的方法，并且还添加了ALiang的更正。它的工作原理。

`/*
 * 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 filen");
    return -1;
}
if (avformat_find_stream_info(i_fmt_ctx, NULL) < 0)
{
    fprintf(stderr, "could not find stream infon");
    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 streamn");
    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 = %dn", 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 filen");
        return -1;
    }
    if (avformat_find_stream_info(i_fmt_ctx, NULL) < 0)
    {
        fprintf(stderr, "could not find stream infon");
        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 streamn");
        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 %lldn", i_pkt.pts, i_pkt.dts);
        static int num = 1;
        printf("frame %dn", 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;
}`

In av_new_stream()

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;

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