[opendtv] Re: (S) DTV adaptors available for less than 50 euros in France
- From: Gary Hughes <ghughesml@xxxxxxxxxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Fri, 16 Sep 2005 09:53:27 -0400
At 12:45 AM 9/16/2005 +0200, Donald Koeleman wrote:
>Gary,
>
>In what you have seen sofar, what is the bandwidth-saving provided by AVC
>over state-of-the-art mpeg2 compression? At IBC some-one at one of the major
>hardware encoder manufacturers told me that in real-live applications it was
>around 25% for HD, and a third to 35% on SD, with a new codec being released
>to operators about once a month. Considering the reference is to operational
>systems, these figures include savings by increased goplength and other such
>tricks (good sense of the word). So how far/long are we removed from
>reaching the promise of cutting bandwidth in half for a given image quality?
I was testing encoding for on-demand applications, comparing to
existing encoding practices which are MPEG-2, 528x480, 3.1mbit/sec CBR
video. We found that encoding AVC at 2mbit/sec, 528x480 and GOP length
of 30 gave comparable quality. In some respects the AVC had a better
looking image, thanks to the deblocking filters in the decoder I suspect.
Dropping the GOP length to 15 decreased the quality somewhat. Dropping
the bitrate had a more dramatic impact. I didn't do much testing with
longer GOP lengths as that begins to impact trick mode performance.
This was with fairly conservative use of AVC features with each GOP starting
with an IDR, one slice per picture, in other words an "MPEG-2 like" structure.
So, I'd say 30-35% reduction in bitrate for SD is realistic with current
products. I expect we will see 50% reduction as people learn how to use
AVC effectively, but my experience suggests that we are in for 12-18 months
of interoperability issues before that becomes real.
gary
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