Pixel format conversion issue [FFMPEG]

问题

I wrote a small program using ffmpeg's libraries. which does the following-

1)decode a frame. 2)convert frame to rgb24 . 3)convert rgb24 frame back to yuv420p. 4)encode the yuv420p frame and pack it into video file.

But the end video is not same as the input video. there is some artifacts in final video (horizontal lines).i also get a warning when the rgbToYuv method gets called - Warning: data is not aligned! This can lead to a speedloss

i suspect something is wrong with my format conversion methods because when i comment the coversion steps from my program the output video is identical to input video.

following are my methods -

int VideoFileInstance::convertToRGBFrame(AVFrame **yuvframe,AVFrame **rgbPictInfo) {
    int ret;
    int width = ifmt_ctx->streams[VIDEO_STREAM_INDEX]->codec->width;
    int height = ifmt_ctx->streams[VIDEO_STREAM_INDEX]->codec->height;

    int m_bufferSize = avpicture_get_size(PIX_FMT_RGB24,width, height);

    uint8_t *buffer = (uint8_t *)av_malloc(m_bufferSize);

    //init context if not done already.
    if (imgConvertCtxYUVToRGB == NULL) {
        //init once
        imgConvertCtxYUVToRGB = sws_getContext(width, height, PIX_FMT_YUV420P, width, height, PIX_FMT_RGB24, SWS_BICUBIC, NULL, NULL, NULL);

        if(imgConvertCtxYUVToRGB == NULL) {
            av_log(NULL,AV_LOG_ERROR,"error creating img context");
            return -1;
        }

    }


    avpicture_fill((AVPicture*)(*rgbPictInfo), buffer,
                   PIX_FMT_RGB24,
                   width, height);

    uint8_t *inDate[3] = {
        (*yuvframe)->data[0] ,
        (*yuvframe)->data[1] ,
        (*yuvframe)->data[2]
    };

    int destLineSize[1] = {3*width};

    ret = sws_scale(imgConvertCtxYUVToRGB, inDate, (*yuvframe)->linesize, 0, height,
              (*rgbPictInfo)->data, destLineSize);

    av_free(buffer);


    return ret;
}

int VideoFileInstance::convertToYuvFrame (AVFrame **rgbFrame , AVFrame ** yuvFrame) {
    int ret = 0;
    int width = ifmt_ctx->streams[VIDEO_STREAM_INDEX]->codec->width;
    int height = ifmt_ctx->streams[VIDEO_STREAM_INDEX]->codec->height;
    int m_bufferSize = avpicture_get_size(PIX_FMT_YUV420P, width, height);

    uint8_t *buffer = (uint8_t *)av_malloc(m_bufferSize);

    avpicture_fill((AVPicture*)(*yuvFrame), buffer, PIX_FMT_YUV420P,
                   width, height);

    if(imgConvertCtxRGBToYUV == NULL) {
        imgConvertCtxRGBToYUV = sws_getContext(width, height, PIX_FMT_RGB24, width, height, PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL);

        if(imgConvertCtxRGBToYUV == NULL){
            av_log(NULL,AV_LOG_ERROR,"error creating img context");
            return -1;
        }
    }

    avpicture_fill((AVPicture*)(*yuvFrame), buffer,
                   PIX_FMT_YUV420P,
                   width, height);




    sws_scale(imgConvertCtxRGBToYUV,(*rgbFrame)->data , (*rgbFrame)->linesize, 0, height,
              (*yuvFrame)->data , (*yuvFrame)->linesize);

    av_free(buffer);

    return ret;
}

The dimention of input video is 424 X 200. Is there anything wrong with my conversion functions.

回答1:

See https://stackoverflow.com/a/31270501/4726410 second bullet point, avpicture_ and related functions don't guarantee alignment, you need to use av_image_ counterparts with align=16 or align=32.

回答2:

Using Ronalds suggestion of using av_image* methods fixed the issue for me. following is fixed code for one of the methods.

int VideoFileInstance::convertToRGBFrame(AVFrame **yuvframe,AVFrame **rgbPictInfo) {
    int ret;
    int width = ifmt_ctx->streams[VIDEO_STREAM_INDEX]->codec->width;
    int height = ifmt_ctx->streams[VIDEO_STREAM_INDEX]->codec->height;




    //init context if not done already.
    if (imgConvertCtxYUVToRGB == NULL) {
        //init once
        imgConvertCtxYUVToRGB = sws_getContext(width, height, PIX_FMT_YUV420P, width, height, PIX_FMT_RGB24, SWS_FAST_BILINEAR, 0, 0, 0);

        if(imgConvertCtxYUVToRGB == NULL) {
            av_log(NULL,AV_LOG_ERROR,"error creating img context");
            return -1;
        }

    }


    // call av_freep(rgbPictInfo->data) to free memory

    av_image_alloc( (*rgbPictInfo)->data,   //data to be filled
                   (*rgbPictInfo)->linesize,//line sizes to be filled
                   width, height,
                   PIX_FMT_RGB24,           //pixel format
                   32                       //aling
                   );



    ret = sws_scale(imgConvertCtxYUVToRGB, (*yuvframe)->data, (*yuvframe)->linesize, 0, height,
              (*rgbPictInfo)->data, (*rgbPictInfo)->linesize);


    return ret;
}

来源：https://stackoverflow.com/questions/31560811/pixel-format-conversion-issue-ffmpeg