```python
import os
from moviepy.editor import *

# Check if required video files exist, if not download them
if not os.path.isfile("video.mp4"):
    os.system("youtube-dl -o video.mp4 <video_url>")
if not os.path.isfile("audio.mp3"):
    os.system("youtube-dl -o audio.mp3 <audio_url>")

# Load audio file, extract subclip, apply fade-in and fade-out effects, analyze audio
audio = AudioFileClip("audio.mp3")
subclip = audio.subclip(10, 20).fadein(2).fadeout(2)
period = subclip.audio.period

# Load video file, extract subclip, crop it, analyze video
video = VideoFileClip("video.mp4")
subclip_video = video.subclip(5, 15).crop(x1=100, x2=500, y1=100, y2=400)
loop_segment = subclip_video.loop()

# Slow down looping segment to match audio tempo, create mirrored version
slow_segment = loop_segment.fx(vfx.speedx, 0.5)
mirrored_segment = slow_segment.fx(vfx.mirror_x)

# Combine original and mirrored segments, apply fade-in and fade-out effects, add audio
final_clip = clips_array([[loop_segment, mirrored_segment]])
final_clip = final_clip.fadein(2).fadeout(2)
final_clip = final_clip.set_audio(audio)

# Create title screen and credits screen
title = TextClip("Title Screen", fontsize=70, color='white').set_duration(5)
credits = TextClip("Credits", fontsize=70, color='white', bg_color='black').set_duration(5)

# Concatenate title screen, video, and credits screen
final_video = concatenate_videoclips([title, final_clip, credits])

# Write final video to file with specified parameters
final_video.write_videofile("output.mp4", fps=24, audio_bitrate="192k", bitrate="5000k")
```