.gmv is the movie capture format of Gens, a Sega Genesis/Megadrive emulator.
GMV file format description
GMV file consists of a 64-byte header and the movie data.
Header format
000 16-byte signature and format version: "Gens Movie TEST9" 00F ASCII-encoded GMV file format version. The most recent is 'A'. (?) 010 4-byte little-endian unsigned int: rerecord count 014 ASCII-encoded controller config for player 1. '3' or '6'. 015 ASCII-encoded controller config for player 2. '3' or '6'. 016 special flags (Version A and up only): bit 7(most significant): if "1", movie runs at 50 frames per second; if "0", movie runs at 60 frames per second bit 6: if "1", movie requires a savestate. bit 5: if "1", movie is 3-player movie; if "0", movie is 2-player movie 018 40-byte zero-terminated ASCII movie name string 040 frame data
}}
Controller Data
Each frame consists of 3 bytes.
| 000 | 001 | 002 |
|---|---|---|
| Controller 1 | Controller 2 | * |
where * is controller 3 if a 3-player movie, or XYZ-mode if a 2-player movie.
For controller bytes, each value is determined by OR-ing together values for whichever of the following are left unpressed:
0x01 Up 0x02 Down 0x04 Left 0x08 Right 0x10 A 0x20 B 0x40 C 0x80 Start
}}
For XYZ-mode, each value is determined by OR-ing together values for whichever of the following are left unpressed:
0x01 Controller 1 X 0x02 Controller 1 Y 0x04 Controller 1 Z 0x08 Controller 1 Mode 0x10 Controller 2 X 0x20 Controller 2 Y 0x40 Controller 2 Z 0x80 Controller 2 Mode
}}
The file has no terminator byte or frame count. The number of frames is the <filesize minus 64> divided by 3.
The file format has no means of identifying NTSC/PAL, but the FPS can still be derived from the header.