Hi, I have three queries related to combining two videos of different aspect ratio, resolution and bitrate.

Is there a tutorial or any resource on how to merge open matte and a 4k video?
Presently the 4k video has black bars at the top and bottom, so basically I would like replace those with information on the top and bottom of the frame from the 1080p open matte video.
Is it possible to preserve HDR information from the 16:9 4K video also?

It appears the two video files are the same length and framerate so I'm hoping syncing should be no issue, however the bitrate is also considerably different, would downscaling the 4k to 1080p be a better option to keep a consistent quality of video with the open matte 1080p?

An ideal solution, if possible, would be to have the video in 4k HDR and full screen.

For reference, here are the media infos of the 4k and 1080p videos:

4K:
Format : HEVC
Format/Info : High Efficiency Video Coding
Format profile : Main 10@L5.1@High
HDR format : SMPTE ST 2086, HDR10 compatible
Codec ID : V_MPEGH/ISO/HEVC
Duration : 2 h 21 min
Bit rate : 59.8 Mb/s
Width : 3 840 pixels
Height : 2 160 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 23.976 (24000/1001) FPS
Color space : YUV
Chroma subsampling : 4:2:0 (Type 2)
Bit depth : 10 bits
Bits/(Pixel*Frame) : 0.300
Stream size : 59.1 GiB (93%)
Writing library : ATEME Titan File 3.8.3 (4.8.3.0)
Default : Yes
Forced : No
Color range : Limited
Color primaries : BT.2020
Transfer characteristics : PQ
Matrix coefficients : BT.2020 non-constant
Mastering display color primaries : Display P3
Mastering display luminance : min: 0.0050 cd/m2, max: 4000 cd/m2
Maximum Content Light Level : 1838 cd/m2
Maximum Frame-Average Light Level : 277 cd/m2

1080p open-matte:
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4
Format settings : CABAC / 4 Ref Frames
Format settings, CABAC : Yes
Format settings, Reference frames : 4 frames
Codec ID : V_MPEG4/ISO/AVC
Duration : 2 h 21 min
Bit rate mode : Variable
Bit rate : 11.9 Mb/s
Maximum bit rate : 15.0 Mb/s
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 23.976 (24000/1001) FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.239
Stream size : 11.8 GiB (95%)
Default : Yes
Forced : No
Color range : Limited
Color primaries : BT.709
Transfer characteristics : BT.709
Matrix coefficients : BT.709

Any help would be much appreciated