HDMV (High Definition Movie) mode is an interactive framework with the well-known features of DVD, but it's more advanced than DVD menus.

It uses a 16 MB memory buffer for graphics. They're stored into the preloading memory buffer before loading the main video, audio, and subtitle streams into the primary memory buffer. HDMV provides multi-stream handling called Out-of-Mux. Out-of-Mux is when the primary stream with individual streams is stored separately but decoded simultaneously in a 27 Mhz clock.

HDMV supports two types of raster bitmap graphics streams for menus and interactive content, the Presentation Graphics stream (available in HDMV and BD-J) is for subtitles and animated graphics, and the Interactive Graphics stream (available only in HDMV) is for interactive menu graphics. IG streams (No file extension name) are separately stored in M2TS files and their decoding process works on a 27MHz clock. To synchronize with the Primary Video and Audio streams, an IG stream operates at a frequency of 90KHz. Like PG streams, IG streams are similar to PNG and use Run Length Encoding for lossless compression to conserve space and memory.

Interactive Graphics are limited to 8-bit 256 colors and alpha transparency, and sprites cannot overlap. They support simple animations such as scrolls, wipes, cuts, fades (transparency changes), and color changes with frame rates up to 30Hz. Supported resolutions are 1920x1080 / 1280x720 / 720x480 / 720x576.

Here's an example of a simple HDMV menu that uses Interactive Graphics (on the right) and AVC video for the background. Made in Abyss S1 D2 (US)

[50000001,00000FEB ,80000004]  Move GPR4075, PSR4 ;PSR4: Title Number (b15-b0) {1-999,$ffff}
[50000001,00000A27 ,00000FEB]  Move GPR2599, GPR4075
[50000001,00000FEB ,00000A27]  Move GPR4075, GPR2599
[50400001,00000FEC ,0000FFFF]  Move GPR4076, 65535
[48000300,00000FEB ,00000FEC]  NE GPR4075, GPR4076
[20810000,00000007 ,00000000]  GoTo 7
[20810000,00000009 ,00000000]  GoTo 9
[20810000,000007D5 ,00000000]  GoTo 2005
[20810000,00000009 ,00000000]  GoTo 9
[50400001,00000FEB ,00000000]  Move GPR4075, 0
[50000001,000009F8 ,00000FEB]  Move GPR2552, GPR4075

On the left, the blue numbers represent the Opcode's hexadecimal value (machine code) and the right represents the Operand GPR/PSR commands. Think of GPRs as controlling the software (the disc) and PSRs as controlling the hardware (the player). 

When you open a Movie Object file in a hex editor, you will see the file's magic number, 4D 4F 42 4A 30 32 30 30, which translates to MOB0100 or MOB0200, letting the player and developer know that this is a Movie Object file.

00000000 4D 4F 42 4A 30 32 30 30 00 00 00 00 00 00 00 00
00000010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00000020 00 00 00 00 00 00 00 00 00 01 38 BA 00 00 00 00
00000030 00 18 80 00 08 63 50 00 00 01 00 00 0F EB 80 00
00000040 00 04 50 00 00 01 00 00 0A 27 00 00 0F EB 50 00
00000050 00 01 00 00 0F EB 00 00 0A 27 50 40 00 01 00 00
00000060 0F EC 00 00 FF FF 48 00 03 00 00 00 0F EB 00 00
00000070 0F EC 20 81 00 00 00 00 00 07 00 00 00 00 20 81
00000080 00 00 00 00 00 09 00 00 00 00 20 81 00 00 00 00
00000090 07 D5 00 00 00 00 20 81 00 00 00 00 00 09 00 00
000000A0 00 00 50 40 00 01 00 00 0F EB 00 00 00 00 50 00

Then you'll see the list of commands in it's hexadecimal values (colored).

[50000001,00000FEB ,80000004]  Move GPR4075, PSR4 ;PSR4: Title Number (b15-b0) {1-999,$ffff}
[50000001,00000A27 ,00000FEB]  Move GPR2599, GPR4075
[50000001,00000FEB ,00000A27]  Move GPR4075, GPR2599
[50400001,00000FEC ,0000FFFF]  Move GPR4076, 65535
[48000300,00000FEB ,00000FEC]  NE GPR4075, GPR4076
[20810000,00000007 ,00000000]  GoTo 7
[20810000,00000009 ,00000000]  GoTo 9
[20810000,000007D5 ,00000000]  GoTo 2005
[20810000,00000009 ,00000000]  GoTo 9
[50400001,00000FEB ,00000000]  Move GPR4075, 0
[50000001,000009F8 ,00000FEB]  Move GPR2552, GPR4075

 It is possible to edit the Movie Object file directly using a hex editor like ImHex or Hexed.it. But it's recommended to use Blu-ray editing software like BDedit or Scenarist. Unless, your a chad and knows each hexadecimal commands by heart.

    See: List of HDMV Commands

General Purpose Registers (GPRs)

A GPR stores a fixed length variable. The variable is stored as a 32-bit unsigned integer. There are 4096 GPRs available. Navigation commands are used to change the values contained in General Purpose Registers. 

In Scenarist, GPRs are written in the program as a number value in square brackets. For example: [ 5 ]. 

In BDedit they are written like this:  GPR5.

    See: List of GPRs

Player Status Registers (PSRs)

A PSR stores a fixed length variable. The variable is stored as a 32-bit unsigned integer. There are 128 PSRs including reserved ones in total. Navigation commands can not change the values contained in PSRs. 

In Scenarist, PSRs are written in the program in three equivalent forms:

1. Number in the curly brackets: { 4 };
2. Name in the curly brackets: { Title };
3. Name with a number in the round brackets in the curly brackets: { Title ( 4 ) }

    See: List of PSRs 

The 2006 release of Memento uses a fancy HDMV menu with animated graphics and sound effects that fit the movie's theme.