Digital Audio and Video Fundamentals: Formats and Concepts

Posted on Apr 3, 2025 in Computers

Digital Sound Characteristics

Sampling rate: This is the number of samples per second taken from an analog sound to convert it into digital format.

Channels: This refers to the number of tracks that make up a sound (e.g., mono, stereo).

Sample size: This indicates the amount of information, in bits, that each sample occupies. A standard CD quality audio uses 16 bits.

Frequency: This is a wave magnitude that indicates the number of complete vibrations occurring per second.

Common Audio Formats

  • WAV: A digital audio format without data compression. It supports mono and stereo files, and its extension is .wav. It is seldom used on the Internet due to file size.
  • MIDI: A protocol for communication between digital musical instruments and computers. Its extension is .midi.
  • CD-A: A standard quality WAV file format that provides digital CD quality.
  • MP3: A compressed sound format using lossy compression. It eliminates sounds that the human ear is not capable of differentiating.

Audacity: Saving and Exporting

To save your audio file on your computer or convert it to another format using Audacity, go to the menu: File > Export (e.g., Export as WAV, Export as MP3, Export as OGG).

Audacity also gives you the ability to save only a selected portion of the waveform. To do this, select a part of the wave and go to the menu: File > Export Selected Audio… (choosing WAV, MP3, OGG Vorbis, etc.).

Image Aspect Ratio

The ratio between the width and height of an image is known as the aspect ratio.

The storage of a DVD movie is often done using anamorphic encoding. Televisions detect the broadcast format to avoid distortions related to aspect ratio.

Video Bit Rate (BR)

The bit stream or bit rate (BR) indicates the number of bits of information transmitted per unit of time in a video. It is measured in bits per second (bit/s).

Different types of bitstreams exist:

  • Constant Bit Rate (CBR)
  • Variable Bit Rate (VBR)

The unit commonly used for bit rate is kbit/s (1 kbit = 1000 bits).

Frames Per Second (FPS) in Video

Frames Per Second (FPS) is the parameter that indicates the number of still images or frames that a digital video displays per second.

Standard FPS values include:

  • Animated film often works at 15 FPS or 24 FPS.
  • PAL TV/video format uses 25 FPS.
  • NTSC TV/video format uses 29.97 FPS.

Common Video Formats

  • AVI: Contains layers of information, typically one for video and one for audio.
  • MOV: The native format for Macintosh; requires QuickTime Player.
  • WMV: Created by Microsoft; supported by its Windows Media Player.
  • RV: A specialized format for streaming (online broadcast via the internet); requires RealPlayer (formerly RealOne Player).
  • MPEG: Uses lossy compression which generally works well. Three main quality levels:
    • MPEG-1: Used in Video-CD (VCD), resolutions like 352×240.
    • MPEG-2: Used in Super Video-CD (SVCD), DVD, and High Definition (HD) video.
    • MPEG-4: Often used for compressing files into formats like AVI (e.g., using DivX codec).
  • FLV: This format is used for videos created with Adobe Flash software.

Digitizing Analog Video Sources

To digitize a VHS video, input from an analog video camera, or even from a television antenna, your computer must have a video capture card.

Digital Video Camera Types

There are primarily 3 types:

  • MiniDV Cameras: Use MiniDV magnetic tape for recording. Connection is typically via FireWire (IEEE 1394).
  • DVD Cameras: Store information directly onto a mini DVD (often rewritable). Allow direct playback of recorded content. Connection is typically via USB.
  • Memory/Hard Drive Cameras: These small cameras use internal memory, memory cards (like SD type), or internal hard drives. Newer models often use hard drives. Connection is via USB or FireWire.

Interactive Multimedia Applications

A multimedia application is considered interactive when the user can change the course of the application by acting upon it.

Peer-to-Peer (P2P) Networks

A peer-to-peer (P2P) network is one that eliminates the need for a central server and directly connects the computers of clients, called nodes.