General Binary Format

General Binary Format

• Each keyframe and chunk is a sequence of blocks.
• Each block starts with a marker byte, which determines its structure.
• A block encapsulates a game packet.
• A chunk contains the S2C packets of the game during its timespan.
• A keyframe contains a set of packets that will recreate the game state at that time.

Marker byte

Marker bits (high to low):

	1 2 3 4
0	0 0 0 0
1	0 0 0 1
2	0 0 1 0
3	0 0 1 1
4	0 1 0 0
5	0 1 0 1
6	0 1 1 0
7	0 1 1 1
8	1 0 0 0
9	1 0 0 1
A	1 0 1 0
B	1 0 1 1
C	1 1 0 0
D	1 1 0 1
E	1 1 1 0
F	1 1 1 1

	5 6 7 8	Channel
0	0 0 0 0	Handshake
1	0 0 0 1	C2S
2	0 0 1 0	Gameplay
3	0 0 1 1	S2C
4	0 1 0 0	Low priority
5	0 1 0 1	Communication
7	0 1 1 0	Loading screen

Bitflags

Bit 1: Time format

• 0 => 4-bytes (float, absolute timestamp, in seconds)
• 1 => 1 byte (uint8, milliseconds since last block)

Bit 2: Include type byte

• 0 => yes
• 1 => no (same as previous block)

Bit 3: Blockparam length

• 0 => 4 bytes
• 1 => 1 byte (relative to previous block)

Bit 4: Bytes reserved for the contentlength

• 0 => 4 bytes
• 1 => 1 byte

Bits 5-8: Channel

• The enet channel in the normal game prototcol
• Probably unimportant for our purposes

Block structure

marker + [time] + [contentlength] + (type) + [blockparam] + [blockcontent]

B3 [00] [C3] (4B) [00] ...
83 [00] [12 02 00 00] (29) [19 00 00 40] ...
A3 [00] [28 01 00 00] (45) [00] ...
F3 [00] [03] [00] ...
93 [00] [07] (FE) [00 00 00 00] ..
73 [XX XX XX XX] [03] [00] ...

Type

• Specifies the kind of packet the block contains
• Is the same as the packet type in the normal game protocol
• The type 0xFE means that the real packet type is the first 2 bytes of the content, allowing types over 0xFF.

Time

• In seconds of game time, specifies when the packet (like an event) occurred and should be replayed.
• It does not (significantly) change in a keyframe.

Blockparam

• The 8-bit values are, like with time, relative to the previous param.
• Specifies the owner of the packet, usually in form of an entity ID.
• If this kind of packet has no owner, it is set to 0

Example keyframe

Start spawn

03
D4 00 FF 44 // float: 2040.02 [time]
02 00 00 00 // [contentlength]
62 // [type]
00 00 00 00 // [blockparam]
00 00 // [blockcontent]

Spawn hero

B3
00 // [time]
C3 // [contentlength]
4C // [type]
00 // [blockparam]
[... 0xC3 bytes ...]

Summoner data

83
00 // [time]
12 02 00 00 // [contentlength]
2A // [type]
19 00 00 40 // EntityID [blockparam]
[... 0x212 bytes ...]

Set inventory

B3
00 // [time]
98 // [contentlength]
FE // [type]
00 // [blockparam]
[... 0x98 bytes ...]

Player stats

A3
00 // [time]
28 01 00 00 // [contentlength]
46 // [type]
00 // [blockparam]
[... 0x128 bytes ...]

Set ability levels

B3
00 // [time]
03 // [contentlength]
15 // [type]
00 // [blockparam]
00 05 00 // [blockcontent] 5 points in q
F3
00 // [time]
03 // [contentlength]
00 // [blockparam]
01 05 00 // [blockcontent] 5 points in w
[etc...]