How Audio and Video Can Be Digitised: Tools and Techniques

Walk into any old college library, sound archive, or family home, and you will likely find shelves of cassette tapes, VHS cartridges, vinyl records, and spools of magnetic tape slowly decaying. The machines that play them are disappearing fast, and the media itself degrades with every passing year. Converting these analog recordings into digital files is the only practical way to preserve and access them. This process, known as digitisation, turns continuous sound and moving images into the binary data that computers can store, copy, and share without further loss. Let us look at exactly how audio and video are digitised, the equipment involved, and the file formats that keep this content alive.

Understanding analog-to-digital conversion 🔗

An analog signal is continuous. The grooves of a record or the magnetic patterns on a tape vary smoothly to represent sound or picture. A computer, however, only understands discrete units, the zeros and ones called bits. The bridge between these two worlds is the analog-to-digital converter (ADC), sometimes called a digitizer. It takes the continuous signal as input and formats it into a serial stream of bits as output, without altering the essential content of the recording.

Two technical settings govern how faithfully this conversion happens. The sampling rate is the frequency at which the converter measures the original signal, given in hertz. An audio CD, for example, is sampled at 44,100 times per second, or 44.1 kHz. The bit depth is the number of bits used for each individual sample, which determines how many discrete levels are available to place that sample. As the National Archives glossary notes, 8 to 10 bit is common for video while 16 to 24 bit is common for audio. Higher values for both settings capture more detail but produce larger files.

Digitising audio 🔗

Audio digitisation is the simpler of the two tasks because sound is one-dimensional data over time. The basic workflow is to connect a playback device to a computer through a converter, then record the incoming stream using software. The choice of equipment depends on the source format.

Equipment for audio capture 🔗

For cassettes, reel-to-reel tape, or any source with a standard line output, an audio interface is the most common tool. The playback device connects to the interface through cables such as RCA leads, and the interface converts the analog signal to digital before passing it to the computer, usually over USB or FireWire. The University of Utah’s Marriott Library, for instance, describes using dedicated recording interfaces and converters connected to a computer to capture the digital bit stream in real time.

For vinyl records, a USB turntable simplifies the chain by building the converter directly into the player. As the record spins, the audio is converted and sent straight to the computer. For fieldwork and live performances, portable digital recorders capture high-quality audio directly onto an SD card or internal memory, which can later be imported into editing software.

Software for audio recording 🔗

Once the analog signal reaches the computer as digital data, recording software acts like a digital tape deck. Audacity, a free and open-source program, is the most widely used choice for libraries and students because it can record, edit, and export in multiple formats. Professional users often turn to Adobe Audition for more advanced cleanup and restoration. The software lets you set the sampling rate and bit depth before recording, which is where preservation standards come into play.

Audio standards for preservation 🔗

For casual listening, CD-quality settings are enough. But archives that want to preserve a recording for the long term aim higher. The International Association of Sound and Audiovisual Archives (IASA) recommends digitising audio at 48 kHz or higher with a bit depth of at least 24 bit, and it suggests 96 kHz as a higher sampling rate for difficult material. The reasoning is that richer files capture inaudible information, support a greater dynamic range, and avoid the need to handle and play fragile originals again. The Smithsonian Institution Archives follows exactly this benchmark, digitising audio as uncompressed Broadcast Wave Format at 24-bit and 96 kHz.

This level of care matters in the Indian context too. The Archives and Research Centre for Ethnomusicology in Gurugram has digitised thousands of hours of rare field recordings of Indian folk and classical music, preserving performances that might otherwise have been lost as the original tapes decayed.

Digitising video 🔗

Video digitisation follows a similar logic but carries added complexity. A video file is really a sequence of still frames combined with a synchronised audio track, so the equipment has to handle far more data per second. Analog formats such as VHS, Betamax, and old film reels all need conversion before they can be stored or viewed on modern devices.

Capture cards and devices 🔗

The central piece of equipment is the video capture card or capture device. It receives the analog video signal, digitises it, and transfers the resulting digital frames to the computer. Capture cards come in two varieties: internal cards installed inside the computer, and external units that plug into a USB port. The analog source, such as a VCR, connects to the card through composite (the yellow, white, and red RCA plugs) or, for better quality, an S-Video connection where available.

Professional preservation projects use high-end cards. Studies of analog videotape digitisation describe workflows built around capture cards that support precise settings, for example a 24-bit depth at 48 kHz for the audio component and 10-bit depth with 4:2:2 chroma sampling for the video. A simpler and popular method among amateurs is to route the analog signal through a digital camcorder or a standalone converter that outputs a DV stream over FireWire, which the computer then records.

Software for video capture 🔗

Once the capture card is connected, software records the incoming digital video. OBS Studio is a free and capable option, while VirtualDub remains a long-standing favourite for capturing and lightly editing analog video. The software controls the frame rate, resolution, and file format of the captured output, and these settings should be matched to the quality of the source rather than pushed artificially high.

Common file formats for digitised media 🔗

After capture, the data is saved in a file format. Understanding these formats means understanding the difference between a codec (the method used to compress the data) and a container (the wrapper that holds the audio, video, and metadata together). Formats fall into three broad families based on compression.

Audio formats 🔗

Uncompressed formats keep all the original data. WAV, developed by Microsoft and IBM, is the standard example and is based on pulse code modulation. It offers the highest quality but produces large files, which is why archives use it for preservation masters. Lossless compressed formats such as FLAC shrink the file to about half the size of WAV while preserving every bit of the original data, making them increasingly popular for storage.

Lossy compressed formats discard information that is hard to hear in order to achieve much smaller files. MP3, which stands for MPEG Audio Layer III, is the most popular of these. Adobe explains that MP3 files can be as small as one-tenth the size of lossless files and work on almost any device, which is why they dominate distribution and streaming. The trade-off, as audio guides point out, is that each lossy export permanently throws away some sound data, so MP3 is best for sharing rather than for the master copy.

Video formats 🔗

On the video side, AVI (Audio Video Interleave), created by Microsoft, is a classic container that can hold video and audio together and was widely used with the early Video for Windows capture tools. It can store high-quality, lightly compressed video but produces large files. Other common containers include MOV, MPEG, and the modern MP4, which pairs efficient codecs with broad device support. For long-term preservation, institutions like the Smithsonian store video as MPEG 4:2:2 and the lossless FFV1 codec, keeping a high-fidelity master separate from the smaller access copies that the public actually views.

Choosing the right approach 🔗

The guiding principle across professional digitisation is to create one high-quality preservation master and then derive smaller access copies from it. Capture at the best settings your equipment and source allow, save that master in an uncompressed or lossless format like WAV or FFV1, and export lighter MP3 or MP4 copies for everyday sharing. Because playback machines and the media themselves are vanishing, each transfer may well be the last one possible from the original, so it pays to do it carefully the first time.

What do you think? If your institution had limited storage, would you prioritise keeping large lossless preservation masters or smaller lossy access copies, and why? And which fragile analog recordings in your own family or community do you think deserve to be digitised before the playback equipment disappears entirely?

References

1. https://www.archives.gov/preservation/products/definitions/terms-glossary
2. https://lib.utah.edu/services/digital-library/AVDigitization.php
3. https://www.iasa-web.org/tc04/key-digital-principles
4. https://siarchives.si.edu/services/digitization
5. https://resources.culturalheritage.org/emg-review/volume-two-2011-2012/capture-software-study-for-preservation-of-analog-videotape/
6. https://www.adobe.com/creativecloud/video/discover/best-audio-format.html
7. https://www.whathifi.com/advice/mp3-aac-wav-flac-all-the-audio-file-formats-explained