RTX Dialogue Audio Format

Container format used for dialogue strings and audio assets (for example ENGLISH.RTX).

Overview

RTX stores two payload kinds under a common chunk/index system:

String-only entries (ASCII text payload)
Audio entries (string metadata + fixed audio header + audio bytes)

The file uses:

per-chunk on-disk headers (tag + big-endian payload size)
a footer that points to a central index table

All values below are validated against ENGLISH.RTX.

File Layout

[chunk records ...]
[index table]
[footer]

Offset (from EOF)	Size	Type	Name	Description
-12	4	ASCII	footer_tag	Always `RNAV`
-8	4	u32 LE	index_offset	Absolute file offset of index table
-4	4	u32 LE	index_count	Number of index entries

For ENGLISH.RTX:

footer_tag = RNAV
index_offset = 184629473
index_count = 4866

Chunk Record (on disk)

Every payload in the data region has an 8-byte chunk header before it:

Offset	Size	Type	Endian	Name	Description
0x00	4	ASCII	—	tag	4-character chunk label
0x04	4	u32	BE	payload_size	Size of payload bytes that follow
0x08	var	`[u8]`	—	payload	Entry payload

Index Table

The index is an array of 12-byte entries. Each entry points to one chunk payload.

Offset	Size	Type	Endian	Name	Description
0x00	4	ASCII	—	tag	Same tag as the chunk header
0x04	4	u32	LE	payload_offset	Absolute file offset of payload (not header)
0x08	4	u32	LE	payload_size	Payload byte size

Validation notes (all 4866 entries):

payload_offset - 8 points to a chunk header with matching tag
header payload_size (big-endian) matches indexed payload_size
all indexed ranges are in bounds (offset + size <= file_size)
entries are ordered by descending payload offset

Payload Types

Payload type is identified by byte payload[1]:

0 = string-only entry
1 = audio entry

String-Only Payload (`payload[1] = 0`)

Offset	Size	Type	Endian	Name	Description
0x00	1	u8	—	kind	Always `0`
0x01	1	u8	—	subtype	Always `0` for text entries
0x02	2	u16	LE	string_len	Byte length of ASCII text
0x04	2	u16	LE	reserved	Always `0`
0x06	var	`[u8]`	—	text	ASCII text bytes, no terminator

Payload size rule:

payload_size = 6 + string_len

Audio Payload (`payload[1] = 1`)

Offset	Size	Type	Endian	Name	Description
0x00	1	u8	—	kind	Always `0`
0x01	1	u8	—	subtype	Always `1` for voice entries
0x02	2	u16	LE	string_len	Byte length of ASCII label
0x04	2	u16	LE	reserved	Always `0`
0x06	var	`[u8]`	—	label	ASCII label bytes, no terminator
0x06+N	27	struct	—	audio_header	Audio metadata (below), `N = string_len`
0x21+N	var	`[u8]`	—	audio_data	Raw PCM audio bytes

Audio payload size rule:

payload_size = 6 + string_len + 27 + audio_length

Audio Header (27 bytes)

All fields little-endian unless noted.

Offset	Size	Type	Name	Description
0x00	4	u32	type_id	`0` = 8-bit mono, `1` = 16-bit mono
0x04	4	u32	bit_depth	`0` = 8-bit, `1` = 16-bit
0x08	4	u32	sample_rate	`11025` or `22050`
0x0C	1	u8	level_0c	Always `100`
0x0D	1	i8	loop_flag	Always `0`
0x0E	4	u32	loop_offset	Always `0`
0x12	4	u32	loop_end	Always `0xFFFFFFFF`
0x16	4	u32	audio_length	Byte length of `audio_data`
0x1A	1	u8	reserved_1a	Always `0`

Notes

Tags are 4-byte IDs and are not globally reused in ENGLISH.RTX.
A few tags include punctuation (for example #bon, ?vql).
The index points to payload starts; on-disk chunk headers are always 8 bytes earlier.

SFX — sound effects container. Uses the same 27-byte audio header structure (offsets 0x00–0x1A) as RTX audio entries. RTX stores voice clips; SFX stores sound effects.

Redguard Preservation CLI

Read

cargo run -- read ENGLISH.RTX parses the file and prints a per-entry summary: tag, type (TEXT or AUDIO), audio format, sample rate, duration, and a label preview.

cargo run -- convert ENGLISH.RTX -o output_dir/ extracts all audio entries as individual .wav files (named by 4-character tag, e.g. zbza.wav) and writes an index.json sidecar containing metadata for all 4866 entries (both text-only and audio).

Validated against ENGLISH.RTX: 3933 .wav files + 933 text entries in index.json.

External References

RGUnity/redguard-unity RGRTXFile.cs | RTX container reader
Dillonn241/redguard-mod-manager RtxDatabase.java | RTX read/write with round-trip support
Dillonn241/redguard-mod-manager RtxEntry.java | RTX entry structure and audio format definitions
UESP: Redguard Console (script command context)

Redguard Preservation Docs