[opendtv] Re: Time to give up on 1080i for football
- From: Tom Barry <trbarry@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Tue, 08 Dec 2009 13:40:36 -0500
John Shutt wrote:
> This is going to come as quite a shock to our four Tandberg encoders that are
> using VBR to statistically multiplex four streams into one ATSC transmission.
>
> I'm not sure how to break the news to them...
>
> John
> ----- Original Message -----
> From: Mike Tsinberg
> To: opendtv@xxxxxxxxxxxxx
>
> The broadcasting such as ATSC can only be done in CBR.
>
They may technically be VBR but I'd wager they still have some fairly
stringent peak bit rate limits that restrict the efficiency of the
encoding for the total program, sort of a compromise between optimizing
the average bit rate over a two hour movie and individually optimizing
each second or so. That is, you can't save up bits displaying a still
scene or talking heads and then apply the bits to a explosion scene 10
minutes later like you could on a BD.
Basically, low latency = reduced encoding efficiency. Even Internet
streaming has an advantage if you allow a bit of tricky buffering.
Though I'll grant averaging over four different streams does help. It
would help a lot more if ATSC had been designed to allow a low latency
low resolution quick channel change stream stat muxed with a high delay
high rez enhancement layer that would appear some extra seconds after
channel change.
- Tom
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