Block diagram
The Resource Interchange File Format (RIFF) is a generic file container format for storing data in tagged chunks. It is primarily used to store multimedia such as sound and video, though it may also be used to store any arbitrary data.
The Microsoft implementation is mostly known through container formats like AVI, ANI and WAV, which use RIFF as their basis.
This page hosts a formal specification of Resource Interchange File Format (RIFF) using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.
meta:
id: riff
title: Resource Interchange File Format (RIFF)
xref:
justsolve: RIFF
loc: fdd000025
wikidata: Q1196805
license: CC0-1.0
endian: le
doc: |
The Resource Interchange File Format (RIFF) is a generic file container format
for storing data in tagged chunks. It is primarily used to store multimedia
such as sound and video, though it may also be used to store any arbitrary data.
The Microsoft implementation is mostly known through container formats
like AVI, ANI and WAV, which use RIFF as their basis.
doc-ref: https://www.johnloomis.org/cpe102/asgn/asgn1/riff.html
seq:
- id: chunk
type: chunk
instances:
chunk_id:
value: chunk.id
enum: fourcc
is_riff_chunk:
value: 'chunk_id == fourcc::riff'
parent_chunk_data:
io: chunk.data_slot._io
pos: 0
type: parent_chunk_data
if: is_riff_chunk
subchunks:
io: parent_chunk_data.subchunks_slot._io
pos: 0
type: chunk_type
repeat: eos
if: is_riff_chunk
types:
chunk:
seq:
- id: id
type: u4
- id: len
type: u4
- id: data_slot
type: slot
size: len
- id: pad_byte
size: len % 2 # if size is odd, there is 1 padding byte
types:
slot: {} # Keeps _io for later use of same substream
parent_chunk_data:
seq:
- id: form_type
type: u4
- id: subchunks_slot
type: slot
size-eos: true
types:
slot: {} # Keeps _io for later use of same substream
chunk_type:
seq:
- id: save_chunk_ofs
size: 0
if: chunk_ofs < 0
- id: chunk
type: chunk
instances:
chunk_ofs:
value: _io.pos
chunk_id:
value: chunk.id
enum: fourcc
chunk_id_readable:
pos: chunk_ofs
size: 4
type: str
encoding: ASCII
chunk_data:
io: chunk.data_slot._io
pos: 0
type:
switch-on: chunk_id
cases:
'fourcc::list': list_chunk_data
list_chunk_data:
seq:
- id: save_parent_chunk_data_ofs
size: 0
if: parent_chunk_data_ofs < 0
- id: parent_chunk_data
type: parent_chunk_data
instances:
parent_chunk_data_ofs:
value: _io.pos
form_type:
value: parent_chunk_data.form_type
enum: fourcc
form_type_readable:
pos: parent_chunk_data_ofs
size: 4
type: str
encoding: ASCII
subchunks:
io: parent_chunk_data.subchunks_slot._io
pos: 0
type:
switch-on: form_type
cases:
'fourcc::info': info_subchunk
_: chunk_type
repeat: eos
info_subchunk:
meta:
encoding: UTF-8
doc: |
All registered subchunks in the INFO chunk are NULL-terminated strings,
but the unregistered might not be. By convention, the registered
chunk IDs are in uppercase and the unregistered IDs are in lowercase.
If the chunk ID of an INFO subchunk contains a lowercase
letter, this chunk is considered as unregistered and thus we can make
no assumptions about the type of data.
seq:
- id: save_chunk_ofs
size: 0
if: chunk_ofs < 0
- id: chunk
type: chunk
instances:
chunk_ofs:
value: _io.pos
chunk_id_readable:
value: id_chars.to_s('ASCII')
chunk_data:
io: chunk.data_slot._io
pos: 0
type:
switch-on: is_unregistered_tag
cases:
false: strz
id_chars:
pos: chunk_ofs
size: 4
is_unregistered_tag:
value: >-
(id_chars[0] >= 97 and id_chars[0] <= 122) or
(id_chars[1] >= 97 and id_chars[1] <= 122) or
(id_chars[2] >= 97 and id_chars[2] <= 122) or
(id_chars[3] >= 97 and id_chars[3] <= 122)
doc: |
Check if chunk_id contains lowercase characters ([a-z], ASCII 97 = a, ASCII 122 = z).
enums:
fourcc:
# little-endian
0x46464952: riff
0x5453494c: list
0x4f464e49: info