The HyperDecks and H.264 Pro Recorder are somewhat different in terms of workflow as the HyperDecks were primarily designed as standalone recording decks while the H.264 Pro Recorder required a USB connection to a computer both for control purposes and as a recording destination.
But the current HyperDeck lineup (and the earlier HyperDeck Studio Mini) do support H.264 recording, so if that is the main objective, they could certainly be used as a replacement. And the current HyperDeck models even have a USB-C port so you can record directly to a USB hard drive, which you could later connect to a computer.
There are some differences in ports and connectivity, as the current HyperDeck models no longer have the component/composite video inputs or analog audio inputs that the H.264 Pro Recorder has. The smallest HyperDeck Studio HD Mini model also lacks an HDMI input (although the larger HyperDeck models have one). The HyperDecks also include some ports like timecode I/O that the H.264 Pro Recorder lacks.
Perhaps the biggest difference that could be an issue for some uses, is that the HyperDecks have a fixed set of bitrate and codec options. On the H.264 Pro Recorder, you could more or less set an arbitrary recording bitrate up to 20 Mbps. Which can be important if you are posting directly to the web, or have limited bandwidth/storage, or have specific target file sizes in mind.
With the HyperDeck models, you are limited to the following options in H.264, each of which has a fixed bitrate that depends on the resolution and frame rate (which is why there is a range specified):
- H.264 High SDI
- H.264 High (45 to 70 Mbps)
- H.264 Medium (25 to 45 Mbps)
- H.264 Low (12 to 20 Mbps)
The H.264 High SDI option is a 10-bit 4:2:2 format, but the bitrate range is not documented. The other options are 8-bit 4:2:0.
These bitrates are actually fairly high for direct web delivery applications, even the H.264 Low setting is 3 to 4 times the kind of data rate that YouTube might use for 1080p video. So they might be overkill if that is the intended destination. But they make more sense when you consider the HyperDeck's intended usage of higher quality recordings for archiving or editing.
And the HyperDeck models also support ProRes and DNxHD which have even higher data rates and quality options if you need them. Additionally, the HyperDeck Studio 4K Pro model supports the following H.265/HEVC codec options: H.265 High SDI, H.265 High, H.265 Medium, H.265 Low.
In terms of long file recording, in the announcement presentation for the new HyperDecks there was mention that you could do recordings of at least 3 hours in a single file, but I can't find any documentation about what the actual single file split duration is (it's possible that it varies somewhat depending on the resolution and codec selected).
For what it's worth in terms of personal experience with both the H.264 Pro Recorder and the H.264 recording on the original HyperDeck Studio Mini, I found the HyperDeck much more reliable and significantly preferred it's more standalone nature and not needing to rely on an easily disconnected USB cable to a computer as the recording medium.