Digital Sound and Video: Formats, Properties, and Tools

Digital Sound Features

Sample Rate: The number of samples per second taken from a continuous analog signal to make a discrete digital signal. For example, CD-quality digital audio uses 44,100 Hz.

Channels: The number of audio channels in a sound recording. Mono = 1, Stereo = 2, 5.1 = 5 channels.

Sample Size: Indicates the number of bits of information in each sample. CD-quality audio uses 16 bits.

Formula: Size = Frequency x Sample Size x Number of Channels x Time (in seconds).

Audio Formats

WAV: A digital audio format without compression. It supports mono and stereo files, and its extension is .wav. It is seldom used on the internet. Microsoft and all programs recognize it.

MIDI: A protocol for communication between digital musical instruments and PCs. Its extension is .midi.

CD-A: A standard of quality for a WAV file that gives digital CD quality. It is a 16-bit WAV file at 44,100 Hz.

MP3: A compressed format with loss. It eliminates the sound that the human ear is unable to differentiate.

Audacity

To save your audio file on your computer or convert it to another format, go to the menu: File, Export as WAV. It also gives you the ability to save only the selected portion of the wave. To do this, select a part of the wave and go to the menu: File, Export Selection as WAV, MP3, or OGG Vorbis.

Video Properties

Proportionality: The ratio between the width and height of the image. It is also known as "aspect ratio." The storage of a DVD movie is done using the anamorphic ratio. The DVD allows the output to fit 16:9 or 4:3 without distortion.

Resolution: The number of pixels of width and height of the capture.

Bitrate: Indicates how many bits of information are transmitted in the video. It is measured in bits per second (bit/s). There are different types of bitrate: constant bitrate and variable bitrate. The unit used to measure bitrate is kbit/s. 1 kbit = 1000 bits.

Frames Per Second (FPS)

This parameter indicates the number of still images or frames that a digital video shows per second.

Standard FPS Values:

• Cartoons: 15 fps
• Film: 24 fps
• PAL Video Format: 25 fps
• NTSC Video Format: 29.97 fps

Video Formats

AVI: Extended by Microsoft and can be used without compression.

MOV: Native format of Macintosh systems. It requires QuickTime Player and is cross-platform.

WMV: Developed by Microsoft as support for its player, Windows Media Player. It is compressed.

RV: A format specializing in streaming. It requires RealOne Player.

MPEG: Compression with loss. There are three quality levels:

• MPEG-1: Used in Video CDs, with resolutions of 352x240.
• MPEG-2: Used in Super Video CDs, DVDs, and High Definition.
• MPEG-4: Used to convert DIVX compressed files in AVI format.

FLV: The format of films made with Flash software. It requires Flash Player to play back compressed files.

Devices

Analog: To digitize a VHS video, a digital video camera, or even from the television antenna, your computer must have a video capture card.

Digital Video Cameras

There are three types:

• MiniDV Cameras: Use a miniDV magnetic tape and have a FireWire connection.
• DVD Cameras: Store information on a rewritable miniDVD. They can directly play back what is recorded. They use USB.
• Memory Cameras: Small cameras that use internal memory or SD-type memory cards. They have a USB or FireWire port.

Multimedia Applications

They are interactive when the user can change the course of the application by acting on it (text, images, videos, etc.).

Peer-to-Peer (P2P) Networks

A peer-to-peer network eliminates the figure of the server and directly connects client computers, called nodes.

Possibilities of Using P2P Networks

• Exchange and search for files.
• Internet telephony.
• Distribution of TV and video on demand.

Intellectual Property Law

Law 23/2006 on private copying states that a person can make a copy for private use of a work already on sale.

Video Editing Software

• Licensed: Adobe Premiere, Pinnacle
• Free: Jahshaka, Cinelerra

Difference Between FLA and SWF Files

Both are made with Flash, but the first one requires Flash to view the video, while the second one does not.