@liammiller - here’s a quick and dirty way to do it with Avidemux. The whole process took about 5 minutes with Avidemux and then I just joined the two files with MKVToolNix. The videos both had identical frame rates and audio, so it was virtually painless. They were two music videos, one 4X3 and the other 16X9 ripped from a DVD.
This will create a 852X480 video. Close enough to 16X9 in my books, and Plex will recognize it as a 480p video.
Start Avidemux
Drag and drop your 4X3 Video into the Avidemux window, or use “File… Open…”
Next, on video output, select MpegAVC (X264), and for audio Output select AC3 (Aften)
You will need to set some filters, I’d start with these ones, and add them in exactly this order:
(you add filters by double clicking on them)
First Filter: under Interlacing, add the Yadif filter. Keep the defaults.
Second filter: under Transform filters, the swsResize filter.
… select NTSC 720X480 DAR 4:3 Par 8:9 as the Source PAR
… select 1:1 (square pixels) as the Destination PAR
… under Resize Dimensions set Width to 640, and Height to 480
Third Filter: under Transform, add the Add Borders filter
… Left Border - 106
… Right Border - 106
… Top Border - 0
… Bottom Border - 0
You can preview the final output by clicking the Preview button while you have the “Add Borders” filter selected.
You can also see a step by step process that each filter does in the chain, by selecting the filter, and hitting preview if you want
Close the Filter Manager. The video on the avidemux window doesn’t change, (or it didn’t for me, anyway)
Choose File… Save… and that’s it. You should end up with a pillar boxed 4X3 video inside a 16X9 frame
You will need to go through a similar process to get the 16X9 in the same format.
You want to end up with a 852X480 video, so basically the same bit of tweaking in the filter section with some different settings.
First Filter: Interlacing Yadif filter
Second filter: Transform - swsResize
… select NTSC 720:480 DAR 16:9 Par 32:27
… select 1:1 (square pixels) as the Destination PAR
… under Resize Dimensions set Width to 852, and Height to 480
(No borders this time)
Close the filter manager and save the file. Use MKVToolNix to append/join the files in the order you want.
You may not need to use the Yadif filter, depending on the source files. You can experiment to get the results that suit you.