Just picked up a Roku Express+ (3910RW) from Walmart to replace my Roku 3 (4200X - 2013) as navigation on that unit is slow.
Everything works great except for the MPEG2 playback. Using either the Plex App (with MPEG2 enabled) or the HDHomeRun app (using an HDHomeRun Quatro), I'm seeing the following issues.
Viewing these same channels / files on my Roku 3 and they play back just fine. Do I have a defective unit or is the Roku 3 from 2013 just more capable than my 2018 Roku Express+?
I'm connected via HDMI to a 1080p TV via a Wireless N connection (as that is all the Express has available). Unit is still on Roku OS 9.1 Example of issue below:
My Premiere was a little choppy with MPEG-2, but disabling framerate matching eliminated that. I've never encountered pixelation at any time. I have encountered buffering, but that's a network issue. Pixelation usually occurs in OTA broadcast TV when the signal isn't sufficient for a good lock. As to why you're getting the strange image sizing I can't guess. I've never had any issue with SD content that is in 4:3 format. But I've never used an HDHomeRun, so I can't speak to how it sends the signal over the network.
Can't be frame rate matching as the Express+ isn't a 4K device. Pixelation only occurs on Plex and HD content on the HDHomerun app. SD content on the HomeRun app is fine, just stretched. The fact that my 6 year old Roku can handle it has me baffled as it's specs are technically lower.
It isn't my reception because I get no Pixelation using the HDHomerun app on the Roku 3 connected to the same network (Wireless / 2.4GHz). The only variable I have come up with is the player.
I don't have any non-4K Roku players, other than my Stick for traveling, so didn't realize they didn't have framerate matching. Bummer.
As to the rest, it does sound odd. The Express+ I would certainly expect to perform better than an older generation player. I can't account for pixelation from an online stream. It just doesn't make sense. There must be something about the way the HDHR app sends the signal, but I can't think of what they could possibly be doing to the signal that makes pixelation something that can happen. I don't know if HDHR has any forums of their own, but I'd try to get some advice from that company or other users.
It has the same stretching phenomenon in Plex and HDHomerun from different sources (Plex from my server and HDHomerun from the OTA signal), so that fact -- same issue, 2 apps from different companies -- along with the fact it works perfectly on my Roku 3 leads me to believe it is the player.
I'm just wondering if it is a hardware issue (I.e. do I need to exchange before these go out of stock) or a software issue that Roku will fix.
Now that I think of it, I'm using the cheap HDMI cable that came with the player, maybe I should try the one I had hooked up to my Roku 3?
Something defective certainly is a possibility. All I can add is I've never had an issue playing SD material. Although I must mention that I rarely use Plex while on my home network. I instead use a different DLNA server (Serviio) and use the Roku Media Player for playback. For me Plex is what I use with my Stick while traveling, as I can connect it to the hotel network and then watch my server content.
If you have a little time to experiment, you might download and try a different DLNA server package, then use RMP and see if the same videos are still pixelating. If you do try Serviio, my only advice is to select a different profile than the default Roku player profile. I wrote the profiles, but I could never get the auto-assign to work accurately. Use the Roku 1080 (2016+) profile or you end up transcoding everything. Since your Express+ probably also supports MPEG-2 video, you could also use use the Roku TV 1080 profile as well, so MEPG-2 doesn't get transcoded.