computer science lecturenovember 29, 2010
- Spatial Compression:
- Compress each frame individually
- Uses the same techniques as JPG compression
- Codecs that do spatial compression are: Animation, PlanarRGB
- Temporal Compression:
- Just saves info on selected frames (called keyframes)
- All other frames just save the difference between current frame and
keyframe is small
- Codecs using temporal compression are: Sorenson Video, H.264
- Container File Format: A file format that stores both the data (frames)
and how to play the data (which codec use)
- Some common containers:
- avi: sometimes has uncompressed videeo, just depends
- flv (swf is not a container file format.)
- mkv (newest and open source. Allows you to store unlimited number
of audio and video tracks. (english/spanish/french all in one avi file.)
- Newer container formats support subtitles, chapters. Why can your
computer sometimes play one avi file but not another one?
- One was built for the codec your computer does have, the other is
built for a codec your computer doesn’t have.
- Digital Media Player: a piece of software that will play multimedia files
(audio or video).
- Most players will play a variety of file formats: ◦
- Windows Media Player (bundled with Windows 7). Some Features (e.g.
- Windows Media Player Question:What is the Apple version of
Windows Media Player for playing video files?
- Question:What is the Apple software developed for playing audio
- Question: Can anyone name another player?
- RealPlayer, VLC
Three Ways of Getting Video to Computer
- Need to know what streaming is for exam*
- Three ways of getting video to computer: download, progressive download,
streaming computer science lecture november 29, 2010
- Streaming: constantly sending to you, downloaded onto your computer
just enough to play it, and then it’s erased from your computer later. It is
never permanently on your computer
- Media is either streamed or not streamed.
- Television is streamed, radio is streamed, a book is not.
- When you visit a website containing video, the entire video must be
downloaded to your computer before you can play it.
- Disadvantages: it takes up space from your hard drive, if you disconnect
from internet you’ll lose the video, you could get a virus, it takes a long time
(hours), it’s not permanent.
- On Demand Streaming and Live Streaming: Live or not live basically.
- You have to have a convert that will convert to a streamed video and a web
server that will let you do streaming
- Video is huge and you want people to watch it immediately so you have to
do lots of compression. RTSP is a special server that lets you do this.
- Progressive Download
- A click begins the download, but after some portion of the file has
been downloaded, the video will start to play and stores it on your
- Advantages: you can watch it while you’re downloading it, you can go
back and play it over again because it’s stored on your computer
- Disadvantage: Your internet could stop working, if your internet slows
down you have to sit and wait for it to download still
- You have to end up with a video that has an RM extension (real medium) for
- STUDY THAT DIAGRAM SHE SHOWED US AT THIS POINT
- Unicast - each user gets own stream, several users get it at once
- Which streaming website has revolutionized video?
- YouTube: Anyone can watch, if you want to post videos you have to
register, some videos only people over 18 can watch, there is