FFMpeg筆記（一） 使用FFmpeg將任意格式圖片轉換成任意格式圖片

void SrcToDest(char* pSrc, char* pDest,unsigned int nSrcWidth, unsigned int nSrcHeight, AVPixelFormat srcFormat,
    unsigned int nDestWidth, unsigned int nDestHeight, AVPixelFormat destFormat)
{
    SwsContext* pConvert_ctx = NULL;
    AVFrame* pFrameIn = NULL;
    AVFrame* pFrameOut = NULL;

    // 分配一個AVFrame，注意必須使用avcodec_free_frame()釋放
    pFrameIn = avcodec_alloc_frame();
    // 使用原始圖片數據填充一個AVFrame
    avpicture_fill((AVPicture*)pFrameIn, (uint8_t*)pSrc, srcFormat, nSrcWidth, nSrcHeight);

    pFrameOut = avcodec_alloc_frame();
    avpicture_fill((AVPicture*)pFrameOut, (uint8_t*)pDest, destFormat, nDestWidth, nDestHeight);
    // linesize[0]是每行的字節數，需根據具體格式調整
    pFrameOut->linesize[0] = nDestWidth * 4;

    // 依據輸入參數獲取格式轉換信息的結構體
    pConvert_ctx = sws_getContext(nSrcWidth, nSrcHeight, srcFormat, \
        nDestWidth, nDestHeight, destFormat, \
        SWS_FAST_BILINEAR, NULL, NULL, NULL);
    // 依據格式轉換結構體，轉換一幀數據
    sws_scale(pConvert_ctx, 
        pFrameIn->data, 
        pFrameIn->linesize, 
        0,
        nSrcHeight, 
        pFrameOut->data, 
        pFrameOut->linesize);

    // 釋放內存
    avcodec_free_frame(&pFrameIn);
    avcodec_free_frame(&pFrameOut);
    sws_freeContext(pConvert_ctx);
}

 　　注意轉換的寬高不能搞錯，否則非但不能轉換正確，還有可能crash。附調試用的保存圖片函數DumpImage，可以使用該函數查看原始數據是否正確或者格式轉換是否成功：

BOOL DumpBmp(const char *filename, uint8_t *pRGBBuffer, int width, int height, int bpp)  
{  
    BITMAPFILEHEADER bmpheader;  
    BITMAPINFOHEADER bmpinfo;  
    FILE *fp = NULL;  

    fp = fopen(filename,"wb");  
    if( fp == NULL )  
    {  
        return FALSE;  
    }  

    bmpheader.bfType = ('M' <<8)|'B';  
    bmpheader.bfReserved1 = 0;  
    bmpheader.bfReserved2 = 0;  
    bmpheader.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);  
    bmpheader.bfSize = bmpheader.bfOffBits + width*height*bpp/8;  

    bmpinfo.biSize = sizeof(BITMAPINFOHEADER);  
    bmpinfo.biWidth = width;  
    bmpinfo.biHeight = 0 - height;  
    bmpinfo.biPlanes = 1;  
    bmpinfo.biBitCount = bpp;  
    bmpinfo.biCompression = BI_RGB;  
    bmpinfo.biSizeImage = 0;  
    bmpinfo.biXPelsPerMeter = 100;  
    bmpinfo.biYPelsPerMeter = 100;  
    bmpinfo.biClrUsed = 0;  
    bmpinfo.biClrImportant = 0;  

    fwrite(&bmpheader,sizeof(BITMAPFILEHEADER),1,fp);  
    fwrite(&bmpinfo,sizeof(BITMAPINFOHEADER),1,fp);  
    fwrite(pRGBBuffer,width*height*bpp/8,1,fp);  
    fclose(fp);  
    fp = NULL;  

    return TRUE;  
}

　　char *pBmpFile = "DumpTest.bmp";
　　DumpBmp(pBmpFile, (uint8_t*)&bufferVector[0],
　　　　DEST_WIDTH_DEFAULT, DEST_HEIGHT_DEFAULT, 32);