Flash player uses 100% + of CPU (mac)

First things first, Flash Player isn't a video player.  Flash Player is a language runtime, much like Java.

You can *write* a video player, in ActionScript, which Flash Player will then execute on your computer.  Moreover, Flash Player pre-dates all of the modern video codecs and the widespread availability of hardware video acceleration.  This means that there's an old-school CPU-only way to publish video, and more modern H.264 video support, which allows us to leverage the dedicated hardware video decoder on your computer.

We publish documentation and guidelines for content providers on how to write a video player that leverages the dedicated graphics hardware on your computer for efficiently decoding and rendering video streams.

In the instance you're describing, we're clearly not leveraging hardware acceleration.  This means that the video is being decoded on the general-purpose CPU, which is less power-efficient, and consumes resources that might otherwise be used by other processes on the system.

It's also possible to do super inefficient things, like streaming video from a source that's a different size than what you're showing on the screen.  When you do that, your computer has to then scale the video to fit the new size, which requires additional operations for every pixel of the video, on every frame.  We discourage developers from doing that for obvious reasons, and we even provide server-side solutions to make it easy to target multiple output sizes and devices.

So, it's one of those things where we provide good documentation to developers, but if you don't read it, it's pretty easy to shoot yourself in the foot.

Since you're on Mac, it's probably one of the following things:

• You're ~10 years behind on Flash Player updates (in which case, update now)
• You explicitly disabled hardware acceleration in Flash Player
  • You'd probably remember doing this.  It's on by default.
• You're already using hardware decoding for something else, and it's unavailable
  • There's a finite amount of stuff that the GPU can do simultaneously.
  • If you're playing a bunch of videos simultaneously, or maybe playing a hardware accelerated game (e.g. Call of Duty, Farmville2), then the GPU may not be available when we try to invoke it, and we fall back to sftware
• The content provider isn't using our hardware-accelerated StageVideo APIs
• The content provider isn't encoding their video stream in a way that allows you to decode it in hardware

As an aside, if the video is encrypted (i.e. it's a DRM-controlled video), like streaming movies or cable shows, then your computer has to decrypt each video frame, which adds a significant amount of overhead (but shouldn't necessarily peg your CPU to 100%).

My guess is that the content provider isn't leveraging the available APIs for hardware accelerated video, and/or they're doing something grossly inefficient (like scaling).

In that vein, silicon codec implementations are picky, and you can't just throw "video" at it.  The hardware codec implementations have very specific guidelines about what they will and won't decode, and there are literally millions of possible encoding combinations, even with just H.264 video.

The set of recommended encoding combinations is much, much smaller, and those are all well-documented in our video publishing guides.  If the content provider isn't publishing the video in an encoding that allows us to use hardware acceleration, we're going to fall back to our software codec.

There are also a lot of legacy video formats besides H.264 that we're able to play, but require decoding in software.  As you've probably guessed, this means that there's CPU overhead; however, those encoding formats tend to be older, and existed in the early 2000s when computers were way slower.

Long story short, this is probably something the content provider could significantly optimize with a little effort (or outsourcing to one of the many video streaming services that cater to this niche).  There's not really much that you personally can do.  It's not something that you're going to fix at the client.  You can also probably find that plenty of video content *does* leverage hardware acceleration, although Flash video on large commercial sites has already largely transitioned to HTML5 video.

You can tell if a video that you're watching is actually Flash Player by right-clicking on it.  If it says About Flash Player at the bottom, it's Flash.  If not, it's probably the browser.

It's also possible that actually powering the computer down (not just doing a quick reboot), letting it sit for a few seconds to fully discharge, and powering it back on might actually help.  A lot of Macbooks swap between a high-end GPU and a low-power, less-capable GPU for maximal battery life.  Sometimes the switching back and forth ends up with things in a freaked out state.  Rebooting would eliminate that possibility, and is a pretty easy experiment.

Sorry that there isn't a magic bullet here.  Video is complicated. 

today videos on the web are not only managed by Flash, but also html5.

So first of all, right click on the video you are watching and tell if you can see "about Adobe Flash..." or something else