This is everything I know about replay files NasCar replay file format: Header (16 bytes): offset size 0 4 Reserved 4 4 Size of data ( length of file - 16 ) 8 4 Time (in 15ths of second) of start of replay ?? C 4 Number of cars (includes pace car ...always present) Records (Variable) Each record represents 1/15 second. In each record there are 13 bytes per car, a graphic objects section (one byte identifying the number of graphic objects followed by the 14-byte graphic objects), a sound objects section (one byte identifying the number of sound objects followed by the 7-byte sound objects), a "flags" section which is one byte and finally a four byte record length field. For each car ( 13 bytes per car) offset size 0 1 bits 1-7 ==> car ID (Note 1,6) bit 0 ==> Car out of race? 1 3 Track linear coordinate (Note 2) 4 2 Track lateral coordinate (Note 3) 6 2 Car Orientation 8 1 Wheel orientation There are sixteen 2-bit damage indicators. The two bits are encoded as follows: 00 - no damage 01 - slight damage to part 10 - major damage to part 11 - part is gone 9 1 Wheel indicators bits 0-1 Right rear wheel bits 2-3 Left rear wheel bits 4-5 Right front wheel bits 6-7 Left front wheel A 1 Body panels bits 0-1 Hood bits 2-3 Grill bits 4-5 Right front fender bits 6-7 Left front fender B 1 Body Panels bits 0-1 Right rear fender bits 2-3 Left rear fender bits 4-5 Right front bumper bits 6-7 Left front bumper C 1 Body Panels bits 0-1 Engine A value of 10 indicates the engine is dead. bits 2-3 Rear bumper bits 4-5 Rear panel bits 6-7 Spoiler and trunk Graphic Objects offset size 0 1 Number of graphic objects (if 0, no fields follow) Object field offset size 0 1 Object type, known types: 01 - smoke 02 - dirt 03 - sparks 04 - sparks 05 - flying tire 0A - All of these have shown up and 0B represent various body panels 0C 0D 0E 0F 1 1 ? (type? altitude?) 2 3 Track linear coordinate 5 2 Track lateral coordinate 7 4 ? B 1 ? (altitude?) Sound Objects offset size 0 1 Number of Sound fields (if 0, no fields follow) Sound field offset size 0 1 ? (always zero?) 1 3 Track linear coordinate 4 2 Track lateral coordinate 6 1 ? (sound type?) Flags offset size 0 1 Flags 01 - Yellow flag 02 - Green flag 04 - White flag 08 - Checkered flag Record Length offset size 0 4 Record length in bytes (used when reading file backwards) Notes: 1. Car ID is a number 0-39 which is the index into the array of cars in the drivers.txt file. 2. Track Linear Position is the distance along the center line of the race track. Rather than use X,Y coordinates, Nascar uses a coordinate system which is distance down the track and distance left or right of the center line. I don't truly understand the units, but it is on the order of 1/2 inch. 3. Track Lateral Position is the distance left/right of the center line. 4. Offsets are in hexadecimal and sizes are in bytes 5. All of the multi-byte fields are in Intel little-endian format. i.e. least significant byte is stored in the lowest addressed byte. 6. When refering to bits within a byte, the bits are numbered with the least significant bit of the byte numbered as bit 0, and the most significant bit of the byte numbered as bit 7. 7. Any field descriptions with question marks (?) represent speculation, best guesses and outright ignorance. This information has been derived from observation of replay files. It may be incorrect and incomplete and is certainly subject to change with different versions of NasCar. It has been sufficient to produce various replay file editors.