[ffmpeg]教程-demuxing&decode&保存YUV420sp

一個簡單的視頻解碼以及保存爲yuv420的小demo

//
//  main.cpp
//  ffmpeg02
//
//  Created by 史明 on 16/10/31.
//  [email protected]
//  gcc -o main.out main.c -lavutil -lavformat -lavcodec -lz
//  compile on mac OS X EI capitan 10.11.6 as following.
//  gcc -o main.out main.c `pkg-config --cflags \
//  --libs  sdl  libavcodec
//  libavformat libavutil ` -lz -lm
//  this demo use libavformat and libavcodec to
//  read video from a file.
//  Copyright © 2016年 史明. All rights reserved.
//

#include <iostream>
#define __STDC_CONSTANT_MACROS

#ifdef _WIN32
//Windows system
extern "C"
{
#include <libavcodec/avcodec.h>
#include "libavformat/avformat.h"
};
#else //_WIN32
//Linux system
#ifdef __cplusplus
extern "C"
{
#endif
#include <libavcodec/avcodec.h>
#include "libavformat/avformat.h"
#ifdef __cplusplus
};
#endif
#endif//_WIN32
#define FRAMECOUNT 5
using namespace std;
//replace the path with your video file
const char *filepath = "/Users/shiming/ffmpegResearch/FFmpeg-Tutorial/ss1-part.mp4";
bool isRuning = true;
void saveFrame(AVFrame * pFrame, int width, int height, int format,int iFrame) {
    FILE *pFile;
    char szFilename[32];
    int  y;


    // Open file
    sprintf(szFilename, "frameout%d.yuv", iFrame);
    pFile=fopen(szFilename, "ab");
    if(pFile==NULL)
        return;

    // Write pixel data
    for(y=0; y<height ; y++)
        fwrite(pFrame->data[0]+y*pFrame->linesize[0], 1, width, pFile);
    for(y=0; y<height / 2; y++) {
        fwrite(pFrame->data[1]+y*pFrame->linesize[1], 1, width / 2, pFile);
    }
    for(y=0; y<height / 2; y++) {
        fwrite(pFrame->data[2]+y*pFrame->linesize[2], 1, width / 2, pFile);
    }
    // Close file
    fclose(pFile);
}

//需要轉化爲rgb的數據纔可以存儲
void saveImg(AVFrame *pFrame, int width, int height, int iFrame) {
    FILE *pFile;
    char szFilename[32];
    int  y;

    // Open file
    sprintf(szFilename, "frame%d.ppm", iFrame);
    pFile=fopen(szFilename, "wb");
    if(pFile==NULL)
        return;

    // Write header
    fprintf(pFile, "P6\n%d %d\n255\n", width, height);

    // Write pixel data
    for(y=0; y<height; y++)
        fwrite(pFrame->data[0]+y*pFrame->linesize[0], 1, width*3, pFile);

    // Close file
    fclose(pFile);
}

void *decodeThread(void *arg) {
    AVFrame* pFrame = av_frame_alloc();
    AVCodecContext* pCodecCtx = (AVCodecContext*)arg;
    int ret = -1;
    int i = 0;
    while (isRuning) {
        ret = avcodec_receive_frame(pCodecCtx, pFrame);
        switch (ret) {
            case 0://成功
                printf("receive a frame !\n");
                saveFrame(pFrame, pCodecCtx->width, pCodecCtx->height, pCodecCtx->colorspace, i++);
                break;
            case AVERROR_EOF:
                printf("the decoder has been fully flushed,\
                       and there will be no more output frames.\n");
                break;

            case AVERROR(EAGAIN):
                printf("Resource temporarily unavailable\n");
                break;

            case AVERROR(EINVAL):
                printf("Invalid argument\n");
                break;
            default:
                break;
        }
    }
    return nullptr;
}

int main(int argc, const char * argv[]) {
    std::cout << "Hello, World!\n";
    int errCode = 0;
    AVFormatContext *pFmtCtx;
    AVInputFormat *pInputFmt;
    AVStream *pStream;
    AVCodec *pCodec;
    AVCodecContext *pCodecCtx;
    AVFrame *pFrame;
    AVPacket *packet;
    AVCodecParameters *pCodecPar;
    pthread_t threadID;

    //註冊所有的格式和編解碼器
    av_register_all();

    //打開文件
    if((errCode = avformat_open_input(&pFmtCtx, filepath, pInputFmt, NULL)) < 0) {
        printf("open input file fail , err code : %d\n", errCode);
        return errCode;
    };


    if((errCode = avformat_find_stream_info(pFmtCtx, NULL)) < 0){
        printf("find stream fail, err code : %d\n", errCode);
        return errCode;
    };
    // Dump information about file onto standard error
    av_dump_format(pFmtCtx, 0, filepath, 0);

    int i;
    int videoStreamID = -1;
    for ( i = 0; i < pFmtCtx->nb_streams; ++i) {
        if(pFmtCtx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
            videoStreamID = i;
            break;
        }
    }

    printf("the first video stream index is : %d\n", videoStreamID);
    pCodecPar = pFmtCtx->streams[videoStreamID]->codecpar;
    pStream = pFmtCtx->streams[videoStreamID];
    printf("codec Par :%d   %d, format %d\n", pCodecPar->width,
           pCodecPar->height, pCodecPar->format);

    pCodec = avcodec_find_decoder(pStream->codecpar->codec_id);
    pCodecCtx = avcodec_alloc_context3(pCodec);
    if((errCode = avcodec_parameters_to_context(pCodecCtx, pStream->codecpar)) < 0) {
        printf("copy the codec parameters to context fail, err code : %d\n", errCode);
        return errCode;
    }
    if((errCode = avcodec_open2(pCodecCtx, pCodec, NULL)) < 0) {
        printf("open codec fail , err code : %d", errCode);
    }

    pFrame = av_frame_alloc();

    //pthread_create(&threadID, NULL, decodeThread, pCodecCtx);
    i = 0;
    packet = av_packet_alloc();
    while (av_read_frame(pFmtCtx, packet) >= 0) {
        if(packet->stream_index == videoStreamID) {
            avcodec_send_packet(pCodecCtx, packet);
            errCode = avcodec_receive_frame(pCodecCtx, pFrame);
            switch (errCode) {
                case 0://成功
                    printf("got a frame !\n");
                    if (i++ < FRAMECOUNT) {
                        saveFrame(pFrame, pCodecPar->width, 
                                pCodecPar->height, pCodecPar->format, i);
                    }
                    break;

                case AVERROR_EOF:
                    printf("the decoder has been fully flushed,\
                           and there will be no more output frames.\n");
                    break;

                case AVERROR(EAGAIN):
                    printf("Resource temporarily unavailable\n");
                    break;

                case AVERROR(EINVAL):
                    printf("Invalid argument\n");
                    break;
                default:
                    break;
            }
        }
        av_packet_unref(packet);
    }
    isRuning = false;
    av_free(pFrame);
    avcodec_close(pCodecCtx);
    avformat_close_input(&pFmtCtx);
    //pthread_join(threadID, NULL);
    std::cout << "Bye, World!\n";
    return 0;
}

早起的版本是使用

int avcodec_decode_video2(AVCodecContext *avctx, AVFrame ＊picture,  int *got_picture_ptr, const AVPacket*avpkt);

我們需要got_picture_ptr來判斷解碼是否成功，但是這是一個阻塞的函數。然而在新的版本中是使用

int avcodec_send_packet(AVCodecContext *avctx, const AVPacket *avpkt);
int avcodec_receive_frame(AVCodecContext *avctx, AVFrame *frame);

avcodec_send_packet和avcodec_receive_frame一定要使用avcodec_open2打開編解碼器。avcodec_send_packet提供原始數據作爲解碼器的輸入。輸入的AVPacket可能是單獨的一個視頻幀，也可能是多個音頻幀。輸入一個flush幀標誌着數據流結束。可以把avpacket置空或者data置空或者size設置成0表示數據流結束的flush幀。avcodec_receive_frame獲取解碼後的數據幀。返回值如上面的源碼。

0表示解碼成功
AVERROR_EOF表示文件尾結束
EAGAIN錯誤碼是35，表示資源暫時不可用，常見的情況就是B幀需要後續的幀重建後纔可能解碼出來。
EINVAL錯誤嗎是22，輸入的參數無效

通過實驗發現，這兩個函數不能在不同的線程去調用，達到異步的效果。也可能着兩個函數只是實現異步的操作的第一步，底層將來可能會支持異步操作。

勞動可貴，歡迎轉載，請註明出處～
http://blog.csdn.net/minger1202/article/details/52468986

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