FFmpeg video from file to network

I am currently working with FFmpeg in a video streaming solution over RTP. What bugs me is how to stream at a correct framerate. Currently I am using a sleep in the main streaming loop:

while (av_read_frame (input_format_ctx, &packet) >= 0) { // Read a video packet as long as EOF is not reached or an error occurr
        if(packet.stream_index == 0) {
            if (av_interleaved_write_frame(output_format_ctx, &packet) < 0) { // Write the packet to the output stream
                av_packet_unref(&packet); // Wipe the packet
                av_free_packet(&packet); // Release the packet and finishes if a problem occured
                break; 
            }
            av_packet_unref(&packet); // Wipe the packet
            av_free_packet(&packet); // Release the packet
        }

        current_time = getSystemTime(); // Get system time
        adaptativeSleep ((last_time + 1/(output_framerate)) - current_time); // Sleep according to framerate
        last_time = getSystemTime(); // Get finish 
    }

Is there a correct way of letting FFmpeg handle the framerate?

Thanks in advance

P.S.: I only remux the stream, as a result FFmpeg runs through the file in a few seconds witought my "sleep".