(59) Multimedia - CS50's Understanding Technology 2017

Understanding Multimedia

• Multimedia refers to the integration of various forms of media, including audio, graphics, and video.

• It plays a significant role in everyday technology use, from computers to mobile devices.

Audio Formats

Overview of Audio in Computers

• Computers excel at recording, playing back, and generating audio through various file formats.

• A file format is a specific way of storing data, allowing software to interpret audio data.

Musical Instrument Digital Interface (MIDI)

• MIDI is a common file format for storing musical notes that represent songs.

• MIDI allows musicians to share music and synthesize instruments on a computer.

• Example: Programs like GarageBand can play MIDI files, synthesizing music based on notes but lacking the quality of a real orchestra performance.

Audio File Formats

• Wave File Format (WAV)

  • One of the earliest formats for high-quality uncompressed audio.

• MP3 (MPEG Layer Audio 3)

  • Uses compression to reduce file size significantly (by more than 10 times).

  • Employs lossy compression, which sacrifices some audio quality to save storage space.

• AAC (Advanced Audio Codec)

  • Commonly used in audio and video files and often employed in platforms like iTunes.

Streaming Services

• Services like Spotify and Apple Music stream audio in real-time, relying on consistent internet bandwidth.

Audio Quality Parameters

• Two primary parameters to consider:

  • Sampling Frequency: Number of samples taken per second.

  • Bit Depth: Number of bits used for each sample to represent audio information.

• A higher bit depth and sampling rate yield better audio quality but require more storage space.

Graphics Formats

Definition of Graphics and Image Representation

• Graphics consists of pixels (dots) arranged in a rectangular grid.

• Each pixel can be represented in binary form (0s and 1s).

Color Representation Using RGB

• RGB (Red, Green, Blue) is the method of color representation in digital images.

• Each color channel (red, green, blue) is represented by 8 bits, allowing for over 16 million possible colors.

Image File Formats

• Bitmap (BMP): Maps pixels as individual bits; less common today.

• GIF (Graphics Interchange Format): Supports animated images but limited to 256 colors due to 8-bit color depth.

• JPEG: Common photo format supporting 24-bit color and utilizes lossy compression. Ideal for photographs.

• PNG: Supports 24-bit color and is used for high-quality graphics, offering lossless compression.

Compression Techniques

• Lossy Compression: Reduces file size by discarding data that may be inaudible or unnoticeable to most users.

• Lossless Compression: Reduces file size without losing any quality, allowing for the original data to be fully recovered.

Video Formats

Overview of Video and Formats

• Videos are a sequence of images played rapidly, creating the illusion of motion (generally 24-30 frames per second).

• Videos can be stored in containers, which can hold video, audio, and additional data (like subtitles).

  • Examples: AVI, MP4, DIVX, QuickTime, Otrosca.

Compression Techniques in Videos

• Intraframe Compression: Similar to GIF; stores the same bits for unchanged pixel colors in frames.

• Interframe Compression: Stores only the differences between consecutive frames, saving storage on redundant data.

Video File Formats

• Encoded video/audio formats might include H.264 for video and AAC for audio within a container.

Emerging Technologies

• Advances in technology now include 3D formats for virtual reality experiences, offering immersive digital environments.

• Metadata in images can enhance how they are presented in VR settings, providing an interactive experience.

Conclusion

• The essence of multimedia and its file formats lies in how bits are organized and utilized. Different file formats provide varying balances of quality, compression, and usability for audio, graphics, and video.