Enforcement Officer / Accounts Officer (EO/AO) 2020 recruitment test, advertisement 421. Transcribed from the Commission's own booklet (series A, NMJX-U-GTA); answer as per the official UPSC final answer key. This question is in Part B. Answer last reviewed 24 August 2026.

Which one of the following is not an audio file format ?

(a)MIDI
(b)WAV
(c)SWF
(d)MPEG

Answer

Why

Correct — C, (c) SWF. SWF stands for Small Web Format, and for most of its life it was known as Shockwave Flash: it is the file format of Adobe Flash, built to carry vector animation, scripted interactivity and streamed multimedia inside a web page, and played by the Flash Player plug-in. A SWF file can certainly contain sound, just as a film reel contains a soundtrack, but the format itself is an animation and multimedia container rather than an audio file format — its defining content is vector shapes, motion and ActionScript. It is also the one option of the four that a candidate today may never have met, because Adobe ended support for Flash Player at the end of 2020 and browsers removed it; HTML5 video, audio and canvas took over the work SWF used to do. The other three options are all part of the audio vocabulary. MIDI and WAV are audio formats of two opposite kinds — one stores instructions for making sound, the other stores the sound itself — and MPEG names the family of standards whose audio layers gave the world MP3 and AAC. The question is built on the fact that a file format can be recognised by the plug-in or player it belongs to as much as by its contents, and SWF belongs to a player that had nothing to do with recorded sound.

Why the others are wrong

(a)MIDI — Musical Instrument Digital Interface, and the most interesting of the audio formats named here because it stores no recorded sound at all. A MIDI file is a sequence of instructions — which note, on which instrument or channel, at what moment, how long, how hard — that a synthesiser or a computer's sound hardware then performs. That makes MIDI files tiny beside recordings and lets any note be edited after the fact, at the price of sounding only as good as the instrument playing them back. It is both a hardware interface standard for electronic instruments and a file format, and it is squarely an audio format, so it is not the intruder.
(b)WAV — The Waveform Audio File Format, developed by Microsoft and IBM, and the textbook example of an audio file. It is a RIFF container that normally holds uncompressed pulse-code-modulated samples — the raw digitised waveform — which is why a WAV file at compact-disc quality is large and why the format is preferred for editing and archiving rather than for distribution. Uncompressed does not mean it is not a format; it is as much an audio format as MP3, only without the compression.
(d)MPEG — MPEG is the Moving Picture Experts Group, and its name attaches to a family of standards rather than to a single file type, which is what makes this option feel like a candidate for the intruder — most people meet MPEG as a video format. But the family's audio layers are the most widely used audio formats there are: MPEG-1 Audio Layer III is MP3, and MPEG-2 and MPEG-4 gave Advanced Audio Coding. The standards define audio coding in their own right and audio-only MPEG files are ordinary things, so MPEG cannot be the option that has nothing to do with sound. SWF can.

Concept

A file format is a convention for laying bytes out so that a program can read back what another program wrote, and the extension is only a label for that convention. Audio formats divide along two lines worth carrying into the exam. The first is what they store: sampled formats hold the digitised waveform itself, while MIDI holds performance instructions to be rendered by an instrument. The second is compression. Uncompressed formats such as WAV and AIFF store the samples as they came from the analogue-to-digital converter. Lossless compressed formats such as FLAC and ALAC shrink the file while allowing the original samples to be reconstructed exactly. Lossy formats such as MP3, AAC, WMA and Ogg Vorbis discard detail the ear is least likely to miss and achieve far smaller files, which is why they carry most streaming and downloading. Beside audio sit the other families the same block likes to test — image formats such as JPEG, PNG, GIF, BMP and TIFF; video and container formats such as MPEG, AVI, MP4, MKV and MOV; document formats such as PDF, DOCX and RTF; and multimedia or animation formats such as SWF. Many of these are containers rather than codecs: MP4 is a wrapper that may hold video coded one way and audio coded another, which is the distinction that makes questions of this shape possible in the first place.

File-format questions are a fixture of the EPFO computer blocks and are asked as odd-one-out items with the negation set in bold italic. They can be prepared for without memorising extensions, by learning the families — image, audio, video, document, archive, animation — and one distinguishing sentence for each of the dozen or so formats that recur. The examiner's construction here is the standard one: three members of a family beside a name from a neighbouring family that carries sound without being about sound. Note also that the acronym is what is printed; the Hindi column spells the same four acronyms out letter by letter, so a candidate reading either column is being asked to recognise a name rather than to parse a description.

Key facts

SWF, originally Shockwave Flash and later Small Web Format, is the vector animation and interactive multimedia format of Adobe Flash, not an audio format.
Adobe ended support for Flash Player at the end of 2020, and its work has been taken over by HTML5 audio, video and canvas.
MIDI, the Musical Instrument Digital Interface, stores instructions for producing sound — note, instrument, timing, velocity — rather than recorded sound, so its files are very small.
WAV, the Waveform Audio File Format from Microsoft and IBM, is a RIFF container that normally holds uncompressed pulse-code-modulated samples.
MPEG names the Moving Picture Experts Group family of standards; MPEG-1 Audio Layer III is MP3 and MPEG-2 and MPEG-4 define Advanced Audio Coding.
Audio formats are uncompressed (WAV, AIFF), lossless compressed (FLAC, ALAC) or lossy compressed (MP3, AAC, WMA, Ogg Vorbis).
A container format such as MP4, AVI or MKV holds streams coded by separate codecs, which is why a single file can carry both video and audio.
Common image formats are JPEG, PNG, GIF, BMP and TIFF; GIF and PNG support transparency and GIF also supports simple animation.

Three names from the audio vocabulary, and one from a plug-in that had nothing to do with sound

SWF→Small Web Format, and for most of its life Shockwave Flash: the file format of Adobe Flash, built to carry vector animation, scripted interactivity and streamed multimedia inside a web page, and played by the Flash Player plug-in. A SWF file can certainly contain sound, just as a film reel contains a soundtrack, but its defining content is vector shapes, motion and ActionScript. It is also the one option a candidate today may never have met: Adobe ended support for Flash Player at the end of 2020 and browsers removed it, HTML5 audio, video and canvas taking over its work.

MIDI→Musical Instrument Digital Interface, and the most interesting of the three because it stores no recorded sound at all. A MIDI file is a sequence of instructions — which note, on which instrument or channel, at what moment, how long, how hard — that a synthesiser or the computer’s sound hardware then performs. That is what makes MIDI files tiny beside recordings, and what lets any note be edited after the fact.

WAV→The Waveform Audio File Format, developed by Microsoft and IBM, and the textbook example of an audio file: a RIFF container that normally holds uncompressed pulse-code-modulated samples, the raw digitised waveform. That is why a WAV file at compact-disc quality is large, and why the format is preferred for editing and archiving rather than for distribution.

MPEG→The Moving Picture Experts Group — a family of standards rather than a single file type, which is what makes this option feel like the intruder, since most people meet MPEG as video. But the family’s audio layers are the most widely used audio formats there are: MPEG-1 Audio Layer III is MP3, and MPEG-2 and MPEG-4 gave Advanced Audio Coding.

The two lines audio formats divide along→WHAT THEY STORE — sampled formats hold the digitised waveform itself, while MIDI holds performance instructions to be rendered by an instrument. COMPRESSION — uncompressed (WAV, AIFF), lossless compressed (FLAC, ALAC), or lossy (MP3, AAC, WMA, Ogg Vorbis), which discard the detail the ear is least likely to miss and so carry most streaming and downloading.

The neighbouring families this block likes to test→Images — JPEG, PNG, GIF, BMP, TIFF, with GIF and PNG supporting transparency and GIF also simple animation. Video and containers — MPEG, AVI, MP4, MKV, MOV. Documents — PDF, DOCX, RTF. Many of these are containers rather than codecs: MP4 is a wrapper that may hold video coded one way and audio coded another, and that distinction is what makes questions of this shape possible at all.

Study next

Families of file formats — image, audio, video, document, archive — and one identifying fact for each common memberLossy against lossless compression, and why the choice differs for photographs, music and archivesContainers against codecs, and what an MP4 or MKV file actually holdsHow sound is digitised — sampling rate, bit depth and the size of the resulting fileThe rise of HTML5 media and the retirement of browser plug-ins such as Flash, Silverlight and Java appletsStreaming against downloading, and the formats and protocols each uses

Common traps

Assuming that because a file can contain sound it is an audio format. SWF, like a video container, may carry sound without being about sound.
Rejecting MPEG because it is thought of as video. Its audio layers are MP3 and AAC.
Thinking MIDI is a recording. It is a set of performance instructions rendered by an instrument or a synthesiser.
Treating WAV as not a real format because it is uncompressed; compression is optional, not definitional.
Skipping the bold-italic 'not'. Three of these four options are audio formats, and the question wants the one that is not.

Extensions and formats come up on nearly every EPFO computer block, usually as an odd-one-out. The same construction has been used for browsers, for operating systems, for input devices and for translators, and the intruder is generally a well-known name from an adjacent category rather than an obscure one. Learn the families and the retired technologies — Flash, floppy disks, dial-up — because the Commission's papers often reach for a name that was current when the syllabus was written.

Related PYQs

EPFO_EOAO_2020_Q29Open & attempt →

Which one of the following is not a web browser ?

(a) Internet Explorer
(b) Firefox
(c) Fedora
(d) Google Chrome

Answer(c) Fedora

The same odd-one-out construction earlier in the paper, asking which of four names is not a web browser.

EPFO_EOAO_2020_Q30Open & attempt →

Which one of the following represents 1 GB of information ?

(a) 1024 KB
(b) 1024 MB
(c) 1024 TB
(d) 1024 PB

Answer(b) 1024 MB

The other standing computer-block topic on file sizes and storage units, asking what represents one gigabyte of information.

EPFO_EOAO_2020_Q66Open & attempt →

Which one of the following is not a language translator ?

(a) Assembler
(b) Linker
(c) Interpreter
(d) Compiler

Answer(b) Linker

Opens this block with the same shape of question, separating the three language translators from the linker.

Practice

practice — not a real PYQ
Which one of the following is a lossless audio compression format ?
- (a)MP3
- (b)FLAC
- (c)AAC
- (d)WMA
Answer(b) FLAC
practice — not a real PYQ
The SWF file format was associated with which one of the following technologies ?
- (a)Adobe Flash
- (b)Java applets
- (c)Microsoft Silverlight
- (d)Apple QuickTime
Answer(a) Adobe Flash

Why