Why Does the TV not deinterlace?

[OneDayAfterAnother]

So I ripped a dvd series....Initially I was going to encode it as I normally do...But I use Roku Ultra to access my Plex and noticed it actually direct plays MPEG 2 and it in fact does...the problem is, when I put the MKV file I make onto the drive and watch it on Plex, I'm seeing interlacing lines all over the place. I've tried 3 modern TVs. I thought TV's themselves handled the deinterlacing. Sorry I wasn't sure where else to ask this question. Thanks

[Woodstock]

TVs aren't supposed to "de-interlace" the source, they just display it as best they can, as you surmise.

However, Plex might be trying to tell the TV that it's removing the interlace, but isn't quite. Can you tell it to feed the original video to the sets, rather than trying to "fix" it?

[pneumatic]

Media players ideally should see that the mpeg2 stream is flagged as interlaced and perform deinterlacing. This includes built in TV media players and standalone set top boxes. However as you have found many will simply ignore the interlace flag and just display the frames "as is". My 2013 Enigma-based PVR sees the flag and deinterlaces, so I must have gotten lucky. Regardless I switched to a HTPC and do my deinterlacing & IVTC in real time with Avisynth filters like BWDIF and TIVTC, and the results are flipping fantastic, especially with a bit of QTGMC antialiasing and MadVR sharpening for some of the softer DVDs. Would highly recommend going the HTPC route. Otherwise you will have to deinterlace your mkv files which includes transcoding and all the downsides that go with that.