4/7 Multimedia Roll call Video Lecture: –multimedia sound –multimedia video Image courtesy of .

4/7 Multimedia

• Roll call

• Video

• Lecture:– multimedia sound– multimedia video

Image courtesy of http://www.wheeloftime.com

Multimedia: What is it?

• Refers to audio and video capabilities of a computer.

• Animation, movies

• stereo sound

• voice recognition

Image courtesy of http://www.GTgames.com

The sound card

• Converts analog to digital and vice versa.

• A coprocessor for the CPU, specialized for dealing with sound processing and compression.

The sound card: recording

• Analog signals from the microphone (or other source) are sent to the ADC (Analog-to-Digital Converter).

• They are converted to digital data.

The sound card: recording

• The digital data is sent to the DSP (Digital Signal Processor), where a ROM chip has the instructions for what to do with the data.

ADC

The sound card: recording

• The DSP sends the processed data off to the CPU.

• Typically, the DSP has compressed the data.

ADC

The sound card: playing

• The DSP receives the compressed data from the CPU.

• Default file type:– WAV

ADC

The sound card: playing

• The DSP decompresses the .WAV file and sends it to the DAC, which converts it and sends it out to the speakers.

ADC

.WAV versus .MIDI files

• WAV files are simply recordings of sounds.

• MIDI files have instructions on how an instrument sounds, and the notes that it will play.

ADC

.WAV versus .MIDI files: analogy

• WAV files are like a disk jockey playing albums.

• MIDI files are like a live band playing requests.

ADC

Multimedia Video

• Multimedia video works similarly to multimedia sound, but stores images and sound.

• .AVI is the default video format. (Audio/Video Interleave)

Multimedia Video

• Compression is more important in video, because there’s more data to store.

• Other file types:– MPEG, MOV,

GIF89a ...

.AVI Compression

• Compression is more important in video, because there’s more data to store.

• Other file types:– MPEG, MOV,

GIF89a ...

.AVI Compression

• The first frame is recorded.

• Blocks of color are recorded not as individual pixels, but a map with information on what color to put there.

.AVI Compression

• To record the next frame, it is compared with the 1st frame.

• Any differences are recorded. The sections that did not change are ignored.

My hair! Aughh!