One obvious one is the audio quality of Twitter videos, or lack thereof. That one immediately told me they were using ffmpeg's AAC encoder (it's fairly obvious on piano music). Some of ffmpeg's built in codecs are great and some aren't; AAC is in the latter category. I've done some ABX tests with it and some transcoding tests and it's just not great; even at 320kbps two or three transcode cycles result in clearly audible artifacts, especially in high frequency sounds like cymbals (you get a sort of warbly characteristic). MP3 actually has better performance in ffmpeg (via LAME) than AAC at the same bitrate, using the built-in encoder.
If you've ever heard a Twitch streamer, especially people playing 8-bit games or chiptune-ish music, and wondered why the audio sounded a bit dodgy, it's ffmpeg. AAC at 160kbps (the streaming standard) is supposed to sound better than that. OBS will use FDK if available, and on macOS and Windows it'll use CoreAudio if installed, but you need to install an old MSI pulled from an old version of iTunes to get that on Windows... so the vast majority of streamers on Windows are stuck with ffmpeg-AAC.
If you're using ffmpeg on Linux, install libfdk and use libfdk_aac; if you're on macOS, use aac_at instead. Those are much better encoders and ffmpeg can use them as external libraries.
Note that this isn't a criticism of ffmpeg; lack of quality in some codecs is a direct result of lack of funding (though I do fault them for, at one time, claiming the built in AAC encoder was good enough to be made the default and competitive with FDK; it wasn't and still isn't, but I think they reverted that claim at some point).
(source: I help run a couple anime DJ restreaming-based events and fixing the AAC issue is a big red warning item in my set-up guide; I once got a double transcode feed where both steps were using ffmpeg-AAC and I could instantly tell something was wrong)
If you've ever heard a Twitch streamer, especially people playing 8-bit games or chiptune-ish music, and wondered why the audio sounded a bit dodgy, it's ffmpeg. AAC at 160kbps (the streaming standard) is supposed to sound better than that. OBS will use FDK if available, and on macOS and Windows it'll use CoreAudio if installed, but you need to install an old MSI pulled from an old version of iTunes to get that on Windows... so the vast majority of streamers on Windows are stuck with ffmpeg-AAC.
If you're using ffmpeg on Linux, install libfdk and use libfdk_aac; if you're on macOS, use aac_at instead. Those are much better encoders and ffmpeg can use them as external libraries.
Note that this isn't a criticism of ffmpeg; lack of quality in some codecs is a direct result of lack of funding (though I do fault them for, at one time, claiming the built in AAC encoder was good enough to be made the default and competitive with FDK; it wasn't and still isn't, but I think they reverted that claim at some point).
(source: I help run a couple anime DJ restreaming-based events and fixing the AAC issue is a big red warning item in my set-up guide; I once got a double transcode feed where both steps were using ffmpeg-AAC and I could instantly tell something was wrong)