Instructions for combining twitch vod+chat into a single 1440p video, using ffmpeg and hardware acceleration.
Example of what it looks like: https://youtu.be/O7fHlel-ScM 

1) Download FFmpeg, FFmpegLauncher and a preset for it, place them in same directory.
- https://github.com/BtbN/FFmpeg-Builds/releases
- https://github.com/syrtsevser/FFmpegLauncher/releases
- https://raw.githubusercontent.com/syrtsevser/FFmpegLauncher/main/presets/VOD%20archiving%20config/FFmpeg%20Launcher.json

2) Download vod, render chat.
Get TwitchDownloader: https://github.com/lay295/TwitchDownloader/releases 
Run TwitchDownloader.exe, download a VOD (.mp4) and it's chat (.json). Make sure they're of same length/duration.
Render chat using following settings: https://imgur.com/a/BW21Nln

3) Combine vod+chat using FFmpeg. Prepare about x4 disk space of original vod's size.
Either use the launcher from step #1, or run FFmpeg manually (commands listed at the end as well).

4) Upload the 1440p video. 
It should get encoded in VP9 regardless of view count.

You're good to go here.


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OPTIONAL: Building a beefy ffmpeg for yourself.
Necessary functionality requires proprietary modules, which is why distributed pre-built ffmpeg builds don't include them. We'll make them.

Prerequisites:
- CUDA Toolkit:			https://developer.nvidia.com/Cuda-toolkit
- Media-autobuild_suite:	https://github.com/m-ab-s/media-autobuild_suite

- Have at least 12 Gb available, the final build will be around 700 Mb. Building itself will take several hours.
- With CUDA installed, run media-autobuild_suite.bat
- Follow instructions, generally self explanatory. Important choices: select "non-free", select "yes, custom ffmpeg options".
- If you get errors during "/making" of ffmpeg, visit ...\build\ffmpeg_options.txt and comment out sketchy modules. 
My options, for example: https://textbin.net/4s9fs9wm8q

Once building has finished (suite should autoclose itself), copy following files into your directory of choice:
- All files from ...\media-autobuild_suite\local64\bin-video\
- C:\Program Files\NVIDIA GPU Computing Toolkit\CUDA\v11.2\bin\nppc64_11.dll
- C:\Program Files\NVIDIA GPU Computing Toolkit\CUDA\v11.2\bin\nppicc64_11.dll
- C:\Program Files\NVIDIA GPU Computing Toolkit\CUDA\v11.2\bin\nppidei64_11.dll
- C:\Program Files\NVIDIA GPU Computing Toolkit\CUDA\v11.2\bin\nppig64_11.dll

Now that ffmpeg is ready, you can uninstall CUDA and remove all MAS files. The copied over files SHOULD get the job done.


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OPTIONAL: Run ffmpeg manually (without launcher).
Open CMD in ffmpeg's folder and run following command:

ffmpeg.exe -i Vod_864p.mp4 -i Chat.mp4 
-c:a copy -map 0:a -c:v hevc_nvenc -preset p7 -tune hq 
-b:v 26M -minrate 24M -fps_mode cfr -r 60 
-temporal-aq 1 -i_qfactor 0.75 -b_qfactor 1.1 -refs:v 16 -rc-lookahead 32 
-bf 3 -b_ref_mode middle -filter_complex "
[0:v]scale=2106:-1:flags=bicubic, setsar=1/1, 
pad=w=2560:h=1440:x=0:y=-1[base]; 
[base][1]overlay=x=main_w-overlay_w:y=main_h-overlay_h" Final_1440p.mp4


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BONUS: Overlaying transparent chat over vod.

1. Generating chat+mask: https://youtu.be/D-_TD1-w3fY
2. FFmpeg instructions and gallery: https://imgur.com/a/F8yDN6v

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