TAV: letterbox detection encoding complete

terranmon.txt

@@ -1007,6 +1007,12 @@ transmission capability, and region-of-interest coding.
     0xE2: ID3v2 packet
     0xE3: Vorbis Comment packet
     0xE4: CD-text packet
+    <Extensible>
+    0x01: Vendor-specific video packets
+    0x02: Vendor-specific audio frame
+    0x03: Vendor-specific subtitle
+    0x04: Vendor-specific audio file
+    0x0E: Vendor-specific metadata
     <Special packets>
     0x00: No-op (no payload)
     0xEF: TAV Extended Header
@@ -1068,6 +1074,16 @@ transmission capability, and region-of-interest coding.
     - Bytes VNDR: Name and version of the encoder (for Reference encoder: "Encoder-TAV 20251014 (list,of,features)")
     - Bytes FMPG: FFmpeg version (typically "ffmpeg version 8.0 Copyright (c) 2000-2025 the FFmpeg developers"; the first line of text FFmpeg emits)
 
+## Extensible Packet Structure
+    uint8  Packet Type
+    uint8  Flags
+           - 0x01: 64-bit size
+    uint8  Identifier[4]
+    <if 64-bit size>
+    uint64 Length of the payload
+    <if not>
+    uint32 Length of the payload
+    *      Payload
 
 ## Standard Metadata Payload Packet Structure
     uint8  Packet Type (0xE0/0xE1/0xE2/.../0xEE; see Packet Types section)