Media ID (MID)

The Media ID (MID) is a unique identifier for a media source. It is constructed from:

1. MAC Address: The 48-bit hardware address of the source device.
2. Pin: The media type identifier, which is a letter followed by a number.

The letter can only be one of the following:

Letter	Pin Type	Binary	Notes
V	Video	00	V0 for first video channel on a device
S	Sound / Audio	01	S0 for first audio channel on a device
T	Text	10	T0 for logs, T1 for GPS
B	Binary	11	Not currently used

The number following the letter can be 0, 1, 2, or 3:

Number	Binary
0	00
1	01
2	10
3	11

The letter and number are encoded together into the MID following the MAC as a single 4-bit nibble, which is done by first shifting the letter's bits left by 2, then combining their binary values with a bitwise OR.

Here is a table of the full MID and its bits:

Bits	Name
0-47	Device MAC
48-49	Pin Letter
50-51	Pin Number

Generating a MID: A Step-by-Step Example

A Media ID (MID) is a single int64 value that packs together a device's MAC address and a pin.

To create a MID, the system parses the MAC address into a 48-bit integer, shifts it left by 4 bits to make room, and then drops a 4-bit pin identifier into that empty space.

Here is a step-by-step example using the MAC address "00:00:00:00:00:0A" and the pin "B2".

Step 1: Encode the MAC Address

First, MacEncode strips the colons from the MAC address and converts the resulting hex string into a network-endian int64.

• Input: "00:00:00:00:00:0A"
• Hex representation: 0x00000000000A
• Integer value: 10

Step 2: Encode the Pin

Next, putMtsPin converts the 2-character string into a 4-bit nibble. The first character (the type) occupies the top two bits, and the second character (the number) occupies the bottom two bits.

• Input: "B2"
• Determine Type: The letter 'B' maps to the top two bits as 11 (which is 0x0C or decimal 12).
• Determine Number: The digit '2' maps to the bottom two bits as 10 (which is 0x02 or decimal 2).
• Combine: 0x0C | 0x02 results in 0x0E (decimal 14).

Step 3: Combine into the Final MID

Finally, ToMID combines these two integers. It takes the encoded MAC, shifts it left by 4 bits (<< 4) to create a 4-bit gap at the end, and then uses a bitwise OR (|) to insert the encoded pin into that gap.

1. Shift the MAC: Take the encoded MAC (0x0A) and shift it left by 4.
   • 0x0A << 4 becomes 0xA0 (decimal 160).
2. Insert the Pin: Apply the bitwise OR with the encoded pin (0x0E).
   • 0xA0 | 0x0E becomes 0xAE
3. Final Integer: The resulting hex value 0xAE is returned as a standard decimal integer.
   • Final MID: 174

Because the bit shift is exactly 4 bits (one hex character), you can easily see how they merged just by looking at the hex values: MAC 0xA + Pin 0xE = MID 0xAE.