Voice File Interchange Protocol (VFIP)
A format for exchanging voice and speech files between different systems over the Internet.
Reynolds, J.K., Gillman, R., Brackenridge, W.A., Witkowski, A., and J. Postel, "Voice File Interchange Protocol (VFIP)", RFC 978, DOI 10.17487/RFC0978, February 1986, <https://www.rfc-editor.org/info/rfc978>.
@misc{rfc978,
series = {Request for Comments},
number = 978,
howpublished = {RFC 978},
publisher = {RFC Editor},
doi = {10.17487/RFC0978},
url = {https://www.rfc-editor.org/info/rfc978},
author = {J.K. Reynolds and R. Gillman and W.A. Brackenridge and A. Witkowski and J. Postel},
title = {{Voice File Interchange Protocol (VFIP)}},
pagetotal = 5,
year = 1986,
month = feb,
} RFC text
Contents
Network Working Group J. K. Reynolds (ISI)
Request for Comments: 978 R. Gillmann (Inner Loop)
W. A. Brackenridge (Alembic)
A. Witkowski (Inner Loop)
J. Postel (ISI)
February 1986
VOICE FILE INTERCHANGE PROTOCOL (VFIP)
STATUS OF THIS MEMO
This memo describes a proposed voice file interchange format for use
in the ARPA-Internet community. Suggestions for improvement are
encouraged. Distribution of this memo is unlimited.
1. INTRODUCTION
The purpose of the Voice File Interchange Protocol (VFIP) is to
permit the interchange of various types of speech files between
different systems. Currently, there are many different types of
voice implementations, but no specific standard has been set with an
eye towards compatability between these systems. With the increasing
interest and development of voice, specifically in Multimedia Mail,
there is an increased need to include standardized speech into a
common data structure.
The Voice File Interchange Protocol defines a header to describe the
voice data. The 18-byte header contains the identifier, the header
version number, the header length, a DTMF mask for Touch-Tones, the
recording rate in bits per second, the total time in deci-seconds
(tenths of a second), and the encoding/recording method (see
Figure 1).
2. THE VOICE FILE INTERCHANGE PROTOCOL HEADER
The Voice File Interchange Protocol header is organized as follows:
2.1 The Header Version Number
The version number is 1-byte. This first version is number one.
2.2 The Header Length
The length is a 1-byte field indicating the length of the entire
header in bytes. For this first version, the length is
18 (bytes).
2.3 The DTMF Mask
This field describes what is known about DTMF Touch-Tones in the
data. The field consists of a 16 flag bits which indicate what is
known about particular DTMF tones. The 16 possible DTMF tones, in
order, are: 0 1 2 3 4 5 6 7 8 9 # * A B C D. The low order bit
of the field is tone 0.
A 1-bit signifies that the corresponding tone is guaranteed NOT to
be in the speech file. A 0-bit signifies that it may or may not
be in the speech file. Therefore, a field of 16 zeros denotes
that nothing is known about the tones. A field of 16 ones denotes
that there are no tones in the file.
2.4 Recording Rate
The recording rate is a 32-bit field and is the approximate rate
in bits/second of the method used to record the speech. For
variable rate methods, this may be very approximate.
2.5 Total Time
A 32-bit number indicating the total time of the recording in
deci-seconds. For example, 600 indicates 1 minute of speech.
2.6 Methods of Encoding/Recording
This 6-byte ASCII field indicates the method of
encoding/recording. Names shorter than six characters are padded
out to the right with blanks (the ASCII space character, code 32
decimal). For comparisons, the names are case insensitive.
Some known methods of Encoding/Recording are:
TI - The Texas Instruments card for the IBM PC [5].
IBM - PC Voice Communications Options.
NVP-1 and NVP-2 - Network Voice Protocol [1,2].
COMPUT - Computalker card for the IBM PC [4].
3. SUMMARY
This 18-byte header will permit interchange of speech files between
different systems, as well as facilitate automatic conversion between
formats. The header does not have to be prepended to the speech file
proper; it may be in the form of a separate associated file, if that
is more convenient.
<------------16-bits------------>
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| -DTMF- |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| -Recording- |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| -Rate- |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| -Total- |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| -Time- |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| M | E |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| T | H |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| O | D |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1
4. EXAMPLES
Example 1 is for one minute of 2400 bps NVP-2 speech. Nothing is
known about DTMF tones in the data.
<------------16-bits------------>
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 | 18 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2400 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 600 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| N | V |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| P | - |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | <sp> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Example 1
Example 2 shows the header for 10 seconds of 1200 bps TI speech, with
none of the DTMF tone 0-9 in the data, but no information about
tones *, #, A-D.
<------------16-bits------------>
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 | 18 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1023 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1200 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 100 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| T | I |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| <sp> | <sp> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| <sp> | <sp> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Example 2
REFERENCES
[1] Cohen, Danny, "Specifications for the Network Voice Protocol
(NVP)", RFC 741 (NIC 42444), USC/Information Sciences Institute,
January 1976.
[2] Cohen, Danny, "A Network Voice Protocol (NVP-II)",
USC/Information Sciences Institute, April 1981.
[3] O'Leary, G. C., "Local Access Area Facilities for Packet Voice",
MIT/LL, October 1980.
[4] Computalker, "Compu Phone for the IBM PC/XT", Santa Monica,
California, August 1985.
[5] Texas Instruments, Inc., "The TI Speech Application Tool Kit
Guide", TI Part #2232384-1, May 1985.
AI ELI5
On this page
§1The Need for a Standard Voice Format
As interest in voice and multimedia mail grew in the 1980s, many different systems started to support voice recordings. However, there was no standard way to exchange voice files between them. A recording made on one system could not be played on another system from a different vendor, making voice communication across the network impossible.
Different companies made different tape machines, and their tapes did not fit in other machines. This protocol lets anyone read any tape.
§2The 18-Byte VFIP Header
Every VFIP voice file starts with an 18-byte header. The header contains a version number (1 byte), the total header length in bytes (1 byte), a DTMF mask indicating which touch-tone digits are in the voice data (2 bytes), the recording rate in bits per second (4 bytes), the total duration in tenths of a second (4 bytes), and a 6-byte ASCII field for the encoding or recording method, padded with spaces.
The header is like a label on a cassette tape that tells you the recording speed, how long it is, and what kind of recorder made it.
§3Encoding Methods
The RFC lists several known encoding methods, including TI (Texas Instruments card for the IBM PC), IBM (PC Voice Communications Options), NVP-1 and NVP-2 (Network Voice Protocol), and COMPUT (Computalker card). The header's method field tells the receiving system which algorithm was used, so it can decode the voice data correctly.
Different tape decks use different tricks to squeeze sound onto tape. The header tells you which trick was used.