if (avformat_seek_file(pFormatCtx, videoStream, INT64_MIN, (int64_t)(pFormatCtx->duration * percent), INT64_MAX, 0) < 0) {
    //avcodec_flush_buffers(pCodecCtx); // tried with and without this, not sure if it's needed
    while(av_read_frame(pFormatCtx, &packet)>=0) {
        // Is this a packet from the video stream?
        if(packet.stream_index==videoStream)
            // Decode video frame
            avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);
            // ...
            SaveFrame();...