[Beowulf] HDTV video file sizes

[Jim Lux]

At 08:49 AM 5/29/2007, laytonjb at charter.net wrote:
>Good morning,
>
>I was doing some thinking over the weekend (while cooking ribs on 
>the grill :)  ).
>Does anyone know who much data 1 hr. of HDTV produces? Let's try 720 for
>now and perhaps 1080. I'm looking for the file size if you store the 
>whole thing
>in a single file.


Are you asking about "as generated in the studio" or "as recorded" or 
"as broadcast"

the raw data rate is >1 Gbps (142.18 Mb/s for NSTC sampled at 14.318 
Ms/s up to 1.486 Gbps for SMTPE 292M sampled at 74.25 Ms/s)



There's several compression/redundancy removal steps in the chain, 
and different HD broadcast media (over the air in US (ATSC), over the 
air in Europe (DVB-T), direct broadcast satellite (DVB-S, and others) 
, cable) use different bit rates, and different compression 
schemes.  And, of course, the DVD (including the new BluRay and 
HD-DVD) have their own encodings as well.

In the US, HD is broadcast over the air in a 6MHz wide channel at 
between 19-20 Mbps (3 bits/symbol).  However, that 20 Mbps stream can 
be divvied up in lots of ways: 1 really HD channel, 5 SD channels, 2 
SD channels plus a medium rate HD channel.

Wikipedia has a lot of info on this..

The appearance of the decoded output depends a LOT on how good the 
encoding was.  You can cheap out and just do simple frame encoding, 
with no frame-to-frame encoding, in which case you get high 
resolution with lots of artifacts. Or, you can spend a lot more 
effort on the encoding, and make use of the frame to frame 
redundancy, and get a lot less artifacts.  The telling difference is 
if you have something like a panning shot over a complex, but fixed, 
background (e.g. a forest in the distance).  A good encoder will be 
able to make use of the fact that big swaths of the image are 
actually the same from frame to frame, just displaced.  A cheap 
encoder will not.

Cable TV and direct broadcast satellite use somewhat different data 
rates (since they have different heritage), and different encodings, sometimes.

Compressed digital video that is intended for further editing is also 
compressed differently, because the "broadcast" compressions tend to 
have unsuitable artifacts in the editing process. Squeezing a raw 
data rate of >1 Gbps down into 20 Mbps or so always entails some 
compromises, and the broadcast compressions are designed to allow 
inexpensive decoders (and expensive encoders..you'll be making 
millions of decoders and dozens of encoders) and for artifacts that 
are visually unobjectionable to an end user.

As you can imagine, there is much opportuntity for transcoding artifacts.

These days, H.264/AVC is probably the leading candidate for compression


So.. for over the air HD broadcasts, 20 Mbps should do you, which is 
well within the range of a variety of hard disks.   Converting to 
GB/hr, I get 8-9 GB/hr


James Lux, P.E.
Spacecraft Radio Frequency Subsystems Group
Flight Communications Systems Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
tel: (818)354-2075
fax: (818)393-6875