Tropic Thunder Commentary Merge (Rear Channel Mix) ================================================== Summary: -------- This project enhances the film "Tropic Thunder (2008 Unrated Directors Cut)" by merging the original 5.1 surround audio with a stereo cast commentary track, cleverly routed only to the rear surround channels. This creates an immersive commentary experience that feels like the cast is sitting on a couch behind you talking about the film. What Was Done: -------------- 1. Original Sources: - Video File: Tropic.Thunder.2008.UNRATED.1080p.BluRay.DDP5.1.x265.10bit-GalaxyRG265.mkv (5.1 EAC3) - Commentary Track: Tropic Thunder Commentary 1- Ben Stiller, Jack Black, Robert Downey.m4a (Stereo) - [renamed both files for simplification] 2. Converted Commentary to 5.1 Layout: - Upmixed stereo to 5.1 and isolated it to the rear channels (SL and SR only) using the following FFmpeg commands: Convert stereo aac to stereo eac3: ffmpeg -i "M:\Movies\Tropic Thunder\CastCommentary.m4a" -c:a eac3 -b:a 192k "M:\Movies\Tropic Thunder\CastCommentary.eac3" Convert stereo eac3 to 5.1 eac3 (special thanks to Anton1699 at r/ffmpeg): ffmpeg -i "CastCommentary.eac3" -filter:a "aresample=resampler=soxr:precision=33:osf=fltp:osr=48000:ochl=5.1(side)" -c:a eac3 -b:a 640k "CastCommentary.5.1.eac3" Isolate stereo channels to the rears (sides): ffmpeg -i CastCommentary.5.1.eac3 -filter_complex "pan=5.1(side)|SL=c0|SR=c1" -c:a eac3 -b:a 640k CastCommentary.rears.eac3 3. Merged Audio Tracks: - Mixed original movie audio (at 40% volume) with the rear-only commentary: ffmpeg -i Tropic.Thunder.2008.UNRATED.mkv -i CastCommentary.rears.eac3 -filter_complex "[0:a:0]volume=0.4[a1]; [a1][1:a:0]amix=inputs=2[aout]" -map 0:v -map "[aout]" -map 0:s? -c:v copy -c:s copy -c:a eac3 -b:a 640k Tropic.Thunder.2008.UNRATED.5.1commentary.mkv 4. Result: - Final file plays the movie normally in 5.1 surround with reduced volume so you can clearly hear the commentary which only comes from the rear speakers (and/or side speakers, depending on your system and speaker layout), perfect for passive listening without disrupting the film. Notes: ------ - DTS encoding was tested but abandoned due to silent output issues. - Best experienced on a true 5.1 (or greater) speaker setup. Special Thanks: --------------- - Admiral of Audio Engineering, MilkyTech - Anton1699 for providing the upmix command from stereo to 5.1 without even knowing it! - ChatGPT for putting it all together ENJOY AND PLEASE SEED!