First, let’s not confusing “mastering for iTunes” with the official program Apple calls “Mastered For iTunes”. At this time, you have to be an approved mastering engineer/studio by Apple in order to submit official “Mastered For iTunes” masters. However, if you’re not on this list, some of the concepts can still apply and be done when you master for iTunes and other streaming/digital stores.
With “Mastered For iTunes”, the main goal is to not have any clipping or overs when your master WAV files are encoded to AAC for the iTunes store. The other benefit is that you can submit 24-bit/high sample rate WAV files for the AAC (end user files) to be encoded from which sound arguably better than 16-bit/44.1k.
The first step about the audio not clipping after the lossy encoding is something you can and should consider for not just iTunes releases but all digital releases. Some mastering engineers leave up to 1dB of headroom to make sure the myriad of encoders the audio will face do not cause the peak levels to exceed 0dBFS and potentially have bad artifacts.
The large majority of digital distributors still ask for 16-bit/44.1k WAV files so all this applies beyond just iTunes releases. You can also still do a standard iTunes release which requires 16-bit/44.1k WAV but you can still make sure there is enough headroom for the AAC encoder to not cause peak levels over 0dBFS.
The second step as mentioned is special to Mastered For iTunes at this time but websites such as Bandcamp and SoundCloud also accept 24-bit/high sample rate files but beware SoundCloud’s port 128kbps audio stream which is sure to induce more clipping and artifacts than something that does 320kbps mp3.
So, I think it’s good practice to be mindful of what happens after lossy encoding no matter what platform you master for because these days, it’s inevitable that the music will be data compressed using a lossy encoder somewhere down the line. Even a CD user these days is likely to just import the CD tracks into their iTunes or media library as a lossy format without even listening to the actual CD.
Anyway, back to your question. WaveLab comes with a similar plugin to the one that Ian Shepherd is using in the video called Encoder Checker. I honestly think the one that Apple provides free is garbage and I don’t use it. Check for a plugin in the master section or Playback Processing slots called Encoder Checker.
Also, one I highly recommend is Sonnox ProCodec (https://www.sonnox.com/plugin/fraunhofer-pro-codec) which I believe is on sale for one more day for their November sale. Aside from what I’ll describe below, it’s a great tool for checking editing/metadata though WaveLab can usually do 99% of the metadata work for you.
What I like about Sonnox ProCodec is that you can analyze the files both in real-time and offline. The offline analysis in my opinion is more useful because you can get repeatable results regarding the peak level changes after encoding. When using these tools on live playback, you get an idea of the sound of the encoder but the peak levels are not 100% repeatable because the bitstream of the codec and the start of the eventual rendered WAV of each track are not in sync. So on live playback, you will see slightly different results with the peak levels. This is discussed in the Sonnox manual.
Unfortunately, at this time there isn’t a codec that is 100% matching the “Mastered For iTunes” (known as iTunes+) available on Windows so that is why Ian says you need to be on a Mac, but Sonnox states that “On Windows computers, the closest approximation to the iTunes Plus codec is the Fraunhofer AAC-LC codec set to highest quality VBR at 256 kbps.”