C/C++ ffmpeg output is low quality and blurry

Question

I've made a program that takes a video file as input, edits it using opengl/glfw, then encodes that edited video. The program works just fine, I get the desired output. However the video quality is really low and I don't know how to adjust it. The editing seems fine, since the display on the glfw window is high resolution. I don'T think its about scaling since it just reads the pixels on the glfw window and passes it to the encoder, and the glfw window is high res.

Here is what the glfw window looks like when the program is running:

I'm encoding in YUV420P formatting, but the information I'm getting from the glfw window is in RGBA format. I'm getting the data using:

   glReadPixels(0, 0,
   gl_width, gl_height, 
   GL_RGBA, GL_UNSIGNED_BYTE, 
   (GLvoid*) state.glBuffer
);

I simply got the muxing.c example from ffmpeg's docs and edited it slightly so it looks something like this:

AVFrame* video_encoder::get_video_frame(OutputStream *ost)
{
    AVCodecContext *c = ost->enc;

    /* check if we want to generate more frames */
    if (av_compare_ts(ost->next_pts, c->time_base,
                      (float) STREAM_DURATION / 1000, (AVRational){ 1, 1 }) > 0)
        return NULL;

    /* when we pass a frame to the encoder, it may keep a reference to it
     * internally; make sure we do not overwrite it here */
    if (av_frame_make_writable(ost->frame) < 0)
        exit(1);

        
    if (c->pix_fmt != AV_PIX_FMT_YUV420P) {           
        /* as we only generate a YUV420P picture, we must convert it
         * to the codec pixel format if needed */
        if (!ost->sws_ctx) {
            ost->sws_ctx = sws_getContext(c->width, c->height,
                                          AV_PIX_FMT_YUV420P,
                                          c->width, c->height,
                                          c->pix_fmt,
                                          SCALE_FLAGS, NULL, NULL, NULL);
            if (!ost->sws_ctx) {
                fprintf(stderr,
                        "Could not initialize the conversion context
");
                exit(1);
            } 
        }
    #if __AUDIO_ONLY
        image_for_audio_only(ost->tmp_frame, ost->next_pts, c->width, c->height);
    #endif

        sws_scale(ost->sws_ctx, (const uint8_t * const *) ost->tmp_frame->data,
                  ost->tmp_frame->linesize, 0, c->height, ost->frame->data,
                  ost->frame->linesize);
    } else {
        //This is where I set the information I got from the glfw window.
        set_frame_yuv_from_rgb(ost->frame, ost->sws_ctx);
    }
    ost->frame->pts = ost->next_pts++;

    return ost->frame;
}

void video_encoder::set_frame_yuv_from_rgb(AVFrame *frame, struct SwsContext *sws_context) {
    const int in_linesize[1] = { 4 * width };
    //uint8_t* dest[4] = { rgb_data, NULL, NULL, NULL };
    sws_context = sws_getContext(
            width, height, AV_PIX_FMT_RGBA,
            width, height, AV_PIX_FMT_YUV420P,
            SWS_BICUBIC, 0, 0, 0);

    sws_scale(sws_context, (const uint8_t * const *)&rgb_data, in_linesize, 0,
            height, frame->data, frame->linesize);
}

rgb_data is the buffer I got from the glfw window. It's simply an uint8_t*.

And at the end of all this, here is what the encoded output looks like when ran through mplayer:

It's much lower quality compare to the glfw window. How can I improve the quality of the video?

C/C++ ffmpeg output is low quality and blurry

0 Answers