feat(remove\_noise.sh): add script to extract, clean and re-insert audio from .mp4 files with noise reduction and normalization

This script does the following:
1. Extracts audio from all .mp4 files using ffmpeg.
2. Takes the first second of the first extracted audio file as a noise sample using SoX.
3. Applies noise reduction and normalization filters to each audio file using SoX.
4. Re-insertes the cleaned audio back into the corresponding videos using ffmpeg.
5. Removes the original audio files and the noise profile file.

remove_noise.sh

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+# 1. extract audio from all videos (assuming .mp4 videos).
+for FILE in *.mp4; do ffmpeg -i $FILE ${FILE%%.mp4}.wav; done
+
+# 2. use the first second of the first audio file as the noise sample.
+sox `ls *.wav | head -1` -n trim 0 1 noiseprof noise.prof
+
+# Replace with a specific noise sample file if the first second doesn't work for you:
+# sox noise.wav -n noiseprof noise.prof
+
+# 3. clean the audio with noise reduction and normalise filters.
+for FILE in *.wav; do sox -S --multi-threaded --buffer 131072 $FILE ${FILE%%.wav}.norm.wav noisered noise.prof 0.21 norm; done
+
+# 4. re-insert audio into the videos.
+# If you need to include an audio offset (+/- n seconds), add parameter "-itsoffset n" after the second -i parameter.
+for FILE in *.norm.wav; do ffmpeg -i ${FILE%%.norm.wav}.mp4 -i $FILE -c:v copy -c:a aac -strict experimental -map 0:v:0 -map 1:a:0 ${FILE%%.norm.wav}.sync.mp4; done
+
+# 5. Remove artefacts
+rm -f *.wav noise.prof
+
+# 6. That's it. You're done!