// elsewhere in the code
if (videoWriter.ffmpegEncoderStart(filename, AV_CODEC_ID_H264, 60, 1920, 1080))
{
    //blah blah
}

bool VideoWriter::ffmpegEncoderStart(const char *filename, int codec_id, int fps, int width, int height) {
    AVCodec *codec;
    int ret;
    avcodec_register_all();
    codec = avcodec_find_encoder((AVCodecID)codec_id);
    if (!codec)
        return false;

    c = avcodec_alloc_context3(codec);
    if (!c)
        return false;

    avcodec_get_context_defaults3(c, codec);

    c->profile = FF_PROFILE_H264_BASELINE;
    c->width = width;
    c->height = height;
    c->time_base.num = 1;
    c->time_base.den = fps;
    c->pix_fmt = AV_PIX_FMT_YUV420P;
    c->gop_size = 10;
    c->level = 50;
    /*mpeg1
    c->bit_rate = 400000;
    c->width = width;
    c->height = height;
    c->time_base.num = 1;
    c->time_base.den = fps;
    c->gop_size = 10;
    c->max_b_frames = 1;
    c->pix_fmt = AV_PIX_FMT_YUV420P;
    */
    if (codec_id == AV_CODEC_ID_H264)
        av_opt_set(c->priv_data, "preset", "slow", 0);
    int returnv = avcodec_open2(c, codec, NULL);
    //if (avcodec_open2(c, codec, NULL) < 0)
    if (returnv < 0) // <- this fails
        return false;

    file = fopen(filename, "wb");
    if (!file)
        return false;

    frame = av_frame_alloc();
    if (!frame)
        return false;
    frame->format = c->pix_fmt;
    frame->width = c->width;
    frame->height = c->height;
    ret = av_image_alloc(frame->data, frame->linesize, c->width, c->height, c->pix_fmt, 32);
    if (ret < 0)
        return false;

    return true;
}