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Home > Archive > Macromedia Flash Server > July 2005 > Flash Com Server- Data Rate Calculation Ambiguity
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Flash Com Server- Data Rate Calculation Ambiguity
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| Megha Vishwanath 2005-07-27, 2:45 am |
| Hi All,
I desperately need help on this,
I read Kevin's article on Encoding practices here-
------------------------------------------------------------------------
-----------------------------------------------------------
I have a sample application to work on Modem bandwidth with an
AVPresence Component -
http://www.macromedia.com/devnet/mx...s/flv_live.html
<http://www.macromedia.com/devnet/mx...v_encoding.html>
According to the calculations for data rate in this article,
My data rate ought to be 120(h) X 160(w) X 6(fps) =115.2 kbps
------------------------------------------------------------------------
-----------------------------------------------------------
There's another article- here
http://www.macromedia.com/devnet/mx...ncoding_02.html
[ Quoting author, I divided by 1000 to convert bps to Kbps, and I've
divided that result by 2.5 because the Sorenson Spark codec has a 2.5:1
compression ratio as you apply it. ]
Accordingly 120 (h) X 160 (w) X 6 (fps) / 2.5 = 46kbps
(Sorenson spark's compression ratio used is 2.5:1 )
With this formula, 160*120*6/2.5 i was actually getting 46.08 kbps data
rates values that are closer to my test video data rate values.
( Cam capturing a rotating fan... so quite a bit of differential data
pushed )
------------------------------------------------------------------------
-----------------------------------------------------------
But both these formulae imply that 1 pixel is encoded as 1 bit, when
there's usually a 24 bit representation 3 (RGB)* 8 bits ?
What we mean by 160*120 = 19200 pixels
and 6 such frames per second is 115200 pixels per second... right?
So the bit - representation still remains a vague.
------------------------------------------------------------------------
-----------------------------------------------------------
Also Sorenson spark's data sheet gives me this formula - W * H * fps /
48000 ( KB/s)
Video data rate calculations aren't making sense to me.
------------------------------------------------------------------------
-----------------------------------------------------------
And audio- I think I found the explanation myself
(Sorenson Spark gives and 8:1 compression ratio for speech)
=> 8k( Sampling Rate) * 16 bit Representation / 8:1
= 16kbps = 2KB/s that concurs with my test audio stream data rates
------------------------------------------------------------------------
-----------------------------------------------------------
I need to work backwards with these values and determine, the bandwidth
we'll need on the server, soon  .
Please, please, help me figure this out,
Thanks and Regards,
Megha Vishwanath,
____________________________
E-Mail: <mailto:meghav-Yr3z5cyCtTJF6kxbq+BtvQ@public.gmane.org> meghav-Yr3z5cyCtTJF6kxbq+BtvQ@public.gmane.org
World2Web Soft Technologies Pvt Ltd.
Bangalore, INDIA 560095
<http://www.world2web.com/> http://www.world2web.com
____________________________
Please visit my Volunteer group at:
<http://www.dsfindia.om/> <http://www.dsfindia.org/>
http://www.dsfindia.org
____________________________
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| |
| Fabio Sonnati 2005-07-27, 7:45 am |
| Indeed, bandwidth formulas are very approximative.
When you set a fixed quality for every frame, as
Flash does, you cannot know the exact amount of
required bandwidth...it may change in a x0.5 - x3 range
depending by the video details (less require bandwidth
for a blurry video, much more for a noise video)
The best approach is to measure the bandwidth with
software like Netpeeker in several camera situation.
Don't use calculations...
----- Original Message -----
From: "Megha Vishwanath" <meghav-Yr3z5cyCtTJF6kxbq+BtvQ@public.gmane.org>
To: <flashcomm-1Ss2GqJETD3yZ38Mhd3e/9ZfFG6BLHNm@public.gmane.org>
Sent: Wednesday, July 27, 2005 7:09 AM
Subject: [FlashComm] Flash Com Server- Data Rate Calculation Ambiguity
> Hi All,
>
> I desperately need help on this,
>
> I read Kevin's article on Encoding practices here-
>
> ------------------------------------------------------------------------
> -----------------------------------------------------------
> I have a sample application to work on Modem bandwidth with an
> AVPresence Component -
>
> http://www.macromedia.com/devnet/mx...s/flv_live.html
> <http://www.macromedia.com/devnet/mx...v_encoding.html>
>
> According to the calculations for data rate in this article,
>
> My data rate ought to be 120(h) X 160(w) X 6(fps) =115.2 kbps
>
> ------------------------------------------------------------------------
> -----------------------------------------------------------
> There's another article- here
>
> http://www.macromedia.com/devnet/mx...ncoding_02.html
>
> [ Quoting author, I divided by 1000 to convert bps to Kbps, and I've
> divided that result by 2.5 because the Sorenson Spark codec has a 2.5:1
> compression ratio as you apply it. ]
>
> Accordingly 120 (h) X 160 (w) X 6 (fps) / 2.5 = 46kbps
> (Sorenson spark's compression ratio used is 2.5:1 )
>
> With this formula, 160*120*6/2.5 i was actually getting 46.08 kbps data
> rates values that are closer to my test video data rate values.
> ( Cam capturing a rotating fan... so quite a bit of differential data
> pushed )
>
> ------------------------------------------------------------------------
> -----------------------------------------------------------
> But both these formulae imply that 1 pixel is encoded as 1 bit, when
> there's usually a 24 bit representation 3 (RGB)* 8 bits ?
> What we mean by 160*120 = 19200 pixels
> and 6 such frames per second is 115200 pixels per second... right?
> So the bit - representation still remains a vague.
>
> ------------------------------------------------------------------------
> -----------------------------------------------------------
> Also Sorenson spark's data sheet gives me this formula - W * H * fps /
> 48000 ( KB/s)
>
> Video data rate calculations aren't making sense to me.
>
> ------------------------------------------------------------------------
> -----------------------------------------------------------
>
> And audio- I think I found the explanation myself
> (Sorenson Spark gives and 8:1 compression ratio for speech)
> => 8k( Sampling Rate) * 16 bit Representation / 8:1
> = 16kbps = 2KB/s that concurs with my test audio stream data rates
>
>
> ------------------------------------------------------------------------
> -----------------------------------------------------------
> I need to work backwards with these values and determine, the bandwidth
> we'll need on the server, soon .
>
> Please, please, help me figure this out,
>
>
> Thanks and Regards,
> Megha Vishwanath,
> ____________________________
> E-Mail: <mailto:meghav-Yr3z5cyCtTJF6kxbq+BtvQ@public.gmane.org> meghav-Yr3z5cyCtTJF6kxbq+BtvQ@public.gmane.org
>
> World2Web Soft Technologies Pvt Ltd.
> Bangalore, INDIA 560095
> <http://www.world2web.com/> http://www.world2web.com
> ____________________________
> Please visit my Volunteer group at:
> <http://www.dsfindia.om/> <http://www.dsfindia.org/>
> http://www.dsfindia.org
> ____________________________
>
>
> =-----------------------------------------------------------
> Supported by Fig Leaf Software - http://www.figleaf.com
> =-----------------------------------------------------------
>
> To change your subscription options or search the archive:
> http://chattyfig.figleaf.com/mailman/listinfo/flashcomm
>
=-----------------------------------------------------------
Supported by Fig Leaf Software - http://www.figleaf.com
=-----------------------------------------------------------
To change your subscription options or search the archive:
http://chattyfig.figleaf.com/mailman/listinfo/flashcomm
| |
| Dario De Agostini 2005-07-28, 7:45 am |
| Hi Megha,
> The best approach is to measure the bandwidth with
> software like Netpeeker in several camera situation.
> Don't use calculations...
i agree... but be warned about this:
different video hardware gives different bw usages
in some situations this difference can be not small at all!
goodluck 
Dario De Agostini
=-----------------------------------------------------------
Supported by Fig Leaf Software - http://www.figleaf.com
=-----------------------------------------------------------
To change your subscription options or search the archive:
http://chattyfig.figleaf.com/mailman/listinfo/flashcomm
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