What is best video format for the whole Apple product line?

Another audio issue. Since upgrading from 10.14.6 to 12.7.1, I've been getting some sound stuttering in various Apple and third party apps.

Audio playback is ‘simple’ enough to process; I doubt that alone causes any CPU strain. But maybe there is something special about your setup and usage. Consider an EtreCheck report if you want to examine if something is holding back the Mac.

I'm trying to eliminate old 32 bit apps and drivers, specifically Blackhole, Camo and Multi-Output device.

32-bit apps and drivers are already eliminated if you are on macOS Monterey 12.x. All 32-bit software is unsupported on macOS 10.15 or later. BlackHole, Camo, Multi Output Device should be available as modern 64-bit software.

Using Activity Monitor it looks like all 4 cores on old 2015 MacBookPro may be pegging.

No cycles wasted; good for the MBP. :-)

Genius Bar said my battery may be limiting power to CPU and Cores.

I would not think that, if they’re official parts, but I’m not GB instructed. The battery should be all-or-nothing. If it works and gives enough voltage, then the computer runs as fine as possible. If the battery is aging and low health, then you would notice frequent low charge levels and frequent recharges. If the battery is aging and low health, then replace that part. With main power connected, the battery is being charged and bypassed as power source, then the computer should run fine.

m4v, mp4, mov are “container” formats, that do not specify what is inside the file per se. These three are pretty much interchangeable. One isn’t better than the other, but when given a choice, pick mp4 for clarity.

If you want to learn what is inside, what is different than the others, what type of video and what type of audio (i.e. codecs), inspect your files with a tool like e.g. Invisor Lite.

For best support among your devices, I would advise to convert your incompatible files to:

MP4 with H.264 AVC video and AAC audio.

A good tool for conversions is: HandBrake.

To convert old obsolete codecs to H.264/H.265 video and AAC audio wrapped as .mp4: Handbrake or Shutter Encoder, I prefer ffmpeg via the Terminal.

Final Cut Pro, DaVinci Resolve or iMovie for editing.

CD+G, like karaoke discs? That’s a blast from 30 years ago, almost mythological. Not sure how that worked without dedicated hardware. Does VLC play those? I think the visuals were timed graphics, but not a real full video track.

Maybe ffmpeg can convert it, but I have no samples to test.