FFMPEG video decoding decapsulation

FFMPEG4.0 audio decoding decapsulated
FFMPEG encoded audio package

The following function method based on the latest FFMPEG 4.0 (4.X):
This article is talking about how to extract a video file from which the image data, the image data and saving to a file.

Decoding and decapsulation procedure similar to audio, as follows:
1. Read the file format information of the video

    fmt_ctx = avformat_alloc_context();
    avformat_open_input(&fmt_ctx,input,NULL,NULL);
    avformat_find_stream_info(fmt_ctx,NULL);

2. Get the video stream

    int st_index = av_find_best_stream(fmt_ctx,AVMEDIA_TYPE_VIDEO,-1,-1,NULL,0);
    LOGV("st_index = %d\n",st_index);
    AVStream *st = fmt_ctx->streams[st_index];

3. Prepare and decoding context ×××

    AVCodec *codec = avcodec_find_decoder(st->codecpar->codec_id);
    AVCodecContext *codec_ctx = avcodec_alloc_context3(codec);

4. Copy video stream parameters to the context and open ××× ×××

    avcodec_parameters_to_context(codec_ctx,st->codecpar);
    avcodec_open2(codec_ctx,codec,NULL);

5. Read the video format, the width and height information

    int width = codec_ctx->width;
    int height = codec_ctx->height;
    enum AVPixelFormat pixel_fmt = codec_ctx->pix_fmt;

6. The image storage application

    uint8_t *dst_buf[4] = {0};
    int      dst_linesize[4];
    int size = av_image_alloc(dst_buf,dst_linesize,width,height,pixel_fmt,1);

packet and frame 7. stated original data is stored after decoded data

    AVFrame *frame = av_frame_alloc();
    AVPacket *packet = av_packet_alloc();

8. The read data, access to video data only

int ret = av_read_frame(fmt_ctx,packet);
//读取到的packet不仅仅是图像数据，还有音频、字幕等数据。
if(packet->stream_index != st_index)
{
    continue;
}

9. The transmission data is decoded
ret = avcodec_send_packet(codec_ctx,packet);
raw data 10. The decoded received, this is an iterative process, a packet may be decoded several frame

        ret = avcodec_receive_frame(codec_ctx,frame);
            if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) //packet解码完了，需要sent
                break;
            if(ret < 0) {
                return 1;
            }

Note: frame received there may be wide or high fmt format change this situation, the process behind the code does not consider this case (should not experience this wonderful video)

            if(frame->width != width || frame->height != height || frame->format != pixel_fmt)
            {
                LOGV("eeeeeeeeeeeee");
            }

11. The copy of the data frame is to dst_buf prepared in advance. Two-dimensional array of pointers seen as an array.
av_image_copy(dst_buf,dst_linesize,frame->data,frame->linesize,pixel_fmt,width,height);
12. The data written to the file.
fwrite(dst_buf[0],1,size,out_file);

Here Posted a complete sample code, the code does not consider the case of failure, the end does not engage in the release, and no flush ×××, the example just to master the entire core decoding process.

/*
 * demuxing_decode_video.c
 *
 *  Created on: 2019年1月8日
 *      Author: deanliu
 */

#include <libavutil/imgutils.h>
#include <libavutil/samplefmt.h>
#include <libavutil/timestamp.h>
#include <libavformat/avformat.h>

static char log_buf[1024*8];
#define LOGV(...) av_log(NULL,AV_LOG_VERBOSE,__VA_ARGS__)

void ffmpeg_log_callback(void* ptr, int level, const char* fmt, va_list vl)
{
    static int print_prefix = 1;
    av_log_format_line(ptr,level,fmt,vl,log_buf,sizeof(log_buf),&print_prefix);
    fprintf(stderr,"%s",log_buf);
}

int main()
{
    av_log_set_callback(ffmpeg_log_callback);

    char *input = "E:/测试音视频/12种格式视频/test.avi";
    char *output = "d:/video.v";

    FILE *out_file = fopen(output,"wb");

    AVFormatContext *fmt_ctx;

    fmt_ctx = avformat_alloc_context();
    avformat_open_input(&fmt_ctx,input,NULL,NULL);
    avformat_find_stream_info(fmt_ctx,NULL);

    int st_index = av_find_best_stream(fmt_ctx,AVMEDIA_TYPE_VIDEO,-1,-1,NULL,0);
    LOGV("st_index = %d\n",st_index);
    AVStream *st = fmt_ctx->streams[st_index];

    AVCodec *codec = avcodec_find_decoder(st->codecpar->codec_id);
    AVCodecContext *codec_ctx = avcodec_alloc_context3(codec);

    avcodec_parameters_to_context(codec_ctx,st->codecpar);
    avcodec_open2(codec_ctx,codec,NULL);

    int width = codec_ctx->width;
    int height = codec_ctx->height;
    enum AVPixelFormat pixel_fmt = codec_ctx->pix_fmt;

    uint8_t *dst_buf[4] = {0};
    int      dst_linesize[4];
    int size = av_image_alloc(dst_buf,dst_linesize,width,height,pixel_fmt,1);

    AVFrame *frame = av_frame_alloc();
    AVPacket *packet = av_packet_alloc();

    while(1)
    {
        LOGV("READ\n");
        int ret = av_read_frame(fmt_ctx,packet);
        if(ret < 0){
            LOGV("ret = %d\n",ret);
            break;
        }
        if(packet->stream_index != st_index)
        {
            continue;
        }
        LOGV("SENT\n");
        ret = avcodec_send_packet(codec_ctx,packet);
        if(ret < 0){
            return 1;
        }

        while(ret >= 0)
        {
            LOGV("receiver\n");
            ret = avcodec_receive_frame(codec_ctx,frame);
            if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
                break;
            if(ret < 0) {
                return 1;
            }
            if(frame->width != width || frame->height != height || frame->format != pixel_fmt)
            {
                LOGV("eeeeeeeeeeeee");
            }
            av_image_copy(dst_buf,dst_linesize,frame->data,frame->linesize,pixel_fmt,width,height);
            LOGV("dst_buf = %d,%d,%d,%d\n",dst_buf[2][0],dst_buf[1][1],dst_buf[0][2],dst_buf[0][3]);
            fwrite(dst_buf[0],1,size,out_file);

        }
    }

    LOGV("dst_linesize = %d,%d,%d,%d\n",dst_linesize[0],dst_linesize[1],dst_linesize[2],size);
    printf("Play the output video file with the command:\n"
           "ffplay -f rawvideo -pix_fmt %s -video_size %dx%d %s\n",
           av_get_pix_fmt_name(pixel_fmt), width, height,
           output);

    LOGV("END!!");

    fclose(out_file);

    return 0;
}