What
is progressive download? How is video streamed live over the internet? All
these questions and more are answered in this article.
Corporate
websites are now embedding helpful 'how to' and 'introductory' video files in
their website pages, and are becoming increasingly aware that their visitors
are far more likely to watch a 3 minute video than to read pages of text.
With
video streaming over the internet now being taken for granted, we have to ask; how
does it work?
Firstly,
we have to break video streaming down into its 3 most commonly used forms.
1)
On demand video streaming
2)
Progressive downloads
3)
Live video streaming
On
demand video
streaming this is where a video content is streamed over the internet
when a website visitor demands it. An example of this is when you click a play
button for a video you want to watch and the video plays. This is very similar
to the 'Progressive download' that we have mentioned except for one main
difference. When a video is streamed it is using streaming server technology.
Steaming servers are a great way to make sure the video is delivered as it
should be. Streaming video with the various streaming server technologies also
allows us to do more than just stream our video. We can actually have 'user
interaction' with our streaming server allowing us to take a video watcher to a
shop to buy something they have seen and 'clicked on' in the video they are
watching for example.
Progressive download: This is where
your video player downloads the whole video into your computer’s memory while
the video is playing.
Live
video streaming: Live video streaming requires a capture device, like a video camera,
encoding software that transcodes or converts the video signal from the camera
into a web compliant video format and a streaming server.
The
video camera will pass on the video information to the encoder, which will send
the transcoded video up to the streaming server (usually over the internet)
using One of the various streaming protocols. The streaming server will then
broadcast the encoded video over the internet to your viewers who will see your
video live, generally with a short delay, commonly about 7 to 20 seconds of
what is happening in real time.
What
is MPEG4? MPEG4 has been designed to allow video playback on a wide variety of
platforms. It can be used on computers, HD TV, PDA's and mobile phones.
Although
there are many different video formats on the internet, the basis for all
streaming, whether live, on demand or progressive download, all work using
similar coding schemes derived from work done for MPEG2, the prior format to
MPEG4.
MPEG4
is made up of 'data channels' used to send the video stream and the audio
stream. The number of data channels is not explicit. Generally we have a video
transport channel that is used to stream the video data, we have up to 8
channels for audio, usually MP3 or AAC (Advance Audio Codec), we have a channel
for subtitles and we have a data channel that allows information to be passed
to and from the streaming server.
The
reason video can be streamed successfully over the web is the delivery method.
Video, especially in films, is delivered frame by frame. This is carried over
from traditional filming methods where each frame contains the full picture
presented to the viewer. These frames are played back one after the other so
quickly that, to the human eye, creates the effect of continuous movement.
Compressed
MPEG4 video is made up of 'I-Frames' and 'P-Frames. I-Frames are effectively
frames that contain all the information needed to display a frame, where a
P-Frame is an update of an I-Frame. So what the decoder does is show an I-frame
and then show a series of P-Frames that update changes in movement etc. Because
of this, the video size is massively reduced. This explains why, when watching
a video over the internet you sometimes see blank squares in the picture. This
is because the P-Frames were not received in time and the decoder cannot update
those areas in the video.
What
is a Codec A Codec is a way of coding and decoding information. So all the
various video formats on the internet work in a similar way, using an encoder
to reduce video and audio data whilst preserving as much quality as possible.
This video is then transmitted over the internet and when it reaches the
clients player it gets decoded into, or as near to, its original format.
The
Codec for video that is gaining popularity is H264. The reason being it works
equally well for TV or mobiles.
No comments:
Post a Comment