From: Steve McMillen <[EMAIL PROTECTED]>
Subject: Re: single bit-rate vs multi bit-rate audio
I beleive the benefits of surestream in terms of the consumer experience far
outweight the costs associated with the additional filesize of a surestream
file. There is a whitepaper if you wish to learn more about SureStream at
http://www.realnetworks.com/devzone/library/whitepapers/index.html.
The primary reason you would want to make use of surestream technology verus
singlerate is to avoid rebuffering in the presentation that can happen as a
result of varying network conditions.
When using singlerate technology, a media file is only capble of streaming at
1 bitrate. That is, if you encode for a target audience of 28k (20kbps
thruput) then the user's modem must maintain a constant 20kbps. If it does
not, then the player will be forced to stop and rebuffer on occasion.
With surestream, you are not limited to only one bandwidth level but rather,
you have a set of bitrates that the server can deliver to the player. Thus,
instead of stopping and rubuffering the server can reduce the thruput from
20kbps down to some lower datarate.
A user is far more likely to loose interest if the stream rebuffers often as
in versus if the stream simply looses some audio or video quality.
In a surestream file the encoder will generally include three levels of video
at 100%, 75% and 50% and up to 3 levels of audio for each target audience.
For example, with a singlerate file a 20kbps stream will have 15 kbps video
and 5kbps of audio, while in a surestream file you would have 15, 11, and 7.5
kbps for levels of video and 5kbps for audio to choose from. So in this
example, if a viewer was streaming a singlerate file their modem would have to
maintain 20kbps or greater thruput or they would experience rebuffering
regularly but if they viewed a surestream they would only need to support
20kbps (15+5), 16 kbps (11+5), OR 12.5kbps (7.5+5). This is great news for
users on _real_ life dial-up connections.
For multiple target audience, such as your example of 28k and 56k, the same is
true of the difference between singlerate and surestream except that now you
have 3 video streams and up to 3 audio streams for each target audience. The
end result of surestream is a filesize of 2x but a user experience many times
better.
Cheers!
[EMAIL PROTECTED]
RealForum wrote:
>
> From: Jaak Simm <[EMAIL PROTECTED]>
> Subject: single bit-rate vs multi bit-rate audio
>
> I using RealServer 7.0 to stream audio with bit-rates 28.8k modem(20kbs) and
> 56k modem (32kbs). I have compered two possibilities for doing that:
> -use two single bit-rate streams (28.8k,56k) to serve audio, the client
> chooses the right connection speed.
> -use one multi bit-rate stream of 28k and 56k to serve audio, the client is
> automatically assigned the right connection speed.
>
> Creating the rm files (with RealProducer 7.0) shows that the multi bit-rate
> file are twice as big as two single bit-rate files together. This fact makes
> me wonder the usefulness of multi bit-rate files as they take up too much
> space.
>
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