Are you sure they said it’ll decode 4k h264 smoothly? I’m seeing them saying 1080p is good, but not 4k.
Here’s a quote from the article you linked, emphasis mine:
RPi5 can software decode AV1, H264, VC1, VP9, and more at 1080p with ease. In our testing with YouTube and inputstream.adaptive a surprising amount of 4K media also plays.
Note that it’s unclear from this quote what Codec the Youtube stream was using, but remember that Youtube is quite low bitrate even at 4k. The implication here is that 1080p h264 is good and low bitrate 4k stuff might be okay, but it will struggle beyond that. Keep in mind that it’s not any worse than RPi 4 in that area, but I don’t think it’s going to be much better either.
You quoted those two sentences, but skipped the three sentences right before them:
BCM2712 supports HEVC 4K60 hardware decoding. It no longer supports H264 in hardware. This might sound odd but it removes the RPi4’s 1080p restriction on H264 decoding and the 4K H264 test media we have has played.
To my eyes this implies it works fine for 4K h264. The sentences you quote from are sort of a “furthermore, at 1080p it can handle these more complex codecs as well” to my initial reading.
I’m not saying you’re wrong, just explaining why I parsed this paragraph a bit differently.
