Re: mpeg storage requirements


Subject: Re: mpeg storage requirements
From: Christopher E. Brown (cbrown@woods.net)
Date: Thu Aug 08 2002 - 03:04:44 AKDT


On Wed, 7 Aug 2002, Greg Jetter wrote:

> On Wednesday 07 August 2002 11:32 am, you wrote:
> > On Tue, 6 Aug 2002, Greg Jetter wrote:
> > > Dose any one know the formula to compute file size of mpegs ? that is to
> > > say if I had 1hr of mpegs how much storage space would it take ?
> > >
> > > Greg
> >
> > You need to know the actual bitrate used, there is not one bitrate
> > (think about mp3s (mpeg2 layer 3 audio), you set the bitrate when
> > recording, bitrate and codec determine quality.
> >
> >
> > Sooo, it will be video bit rate + audio bit rate. As to what those
> > are...
>
> thanks chris
>
> what about compression , does that figure in ?

Yes, but the stated bit rate for mpeg audio, mpeg video or mpeg
audio+video is *after* compression.

Sooo, take a mpeg4 video + mpeg2 layer3 stereo audio stream for
example. Say a 2.5Mbit/sec video stream + a 128Kbit audio stream (as
found in a fairly standard SVCD stream.

Since bit rates are in line rates they use base 10 notation (Megabit
is 1,000,000 bits, not 1,048,576 bits as used in computer storage).

So, 2,500,000 bits/sec + 128,000 bits/sec = 2,628,000 bits/sec, or a
2.628Mbit/sec stream. Converting to storage notation (1024*1024 mega
instead of 1000*1000) it is 320.8 KBytes of file per second of stream,
or 19,248 KBytes per minuet. 19,248KBytes/min is of course 18.79
MegaBytes per minuet.

To give a real world example from a real DVD stream.

1:41 of DVD video (mpeg4 720x480) and audio (ac52 encoding) is 4,813
MegaBytes for 101 minuets, or 47.65 MegaBytes/min, . So, we have a
stream of 6,662,437 bits/sec, or 6.66 Mbits/sec in line notation.

Just remember, bit rate is *after* compression.

Combine the video and audio bit rates for multiplexed streams (if not
already displayed this way) before figuring.

Convert from line rate to storage notation

So, 1hr of DVD video with 5 channel audio, is about 2,859MB or 2.8GB.

And 1hr of 128kbit mpeg2 layer3 (.mp3 audio) is 55MB.
128,000 / (1,024 * 1,024) * (60 * 60) / 8 = 54.93 MegaBytes/hr

-- 
I route, therefore you are.

--------- To unsubscribe, send email to <aklug-request@aklug.org> with 'unsubscribe' in the message body.



This archive was generated by hypermail 2a23 : Thu Aug 08 2002 - 03:22:36 AKDT