[opendtv] Re: Lip sync problem resurfaces
- From: jeroen.stessen@xxxxxxxxxxx
- To: opendtv@xxxxxxxxxxxxx
- Date: Tue, 20 Apr 2004 11:38:13 +0200
Hello,
Frank Eory replied:
> So the audio should be deliberately delayed at the STB outputs,
> thus skewing A/V sync for CRTs?
Yes, if it is true that the viewer tolerates audio delay better than
video delay. We have always accepted that the thunder comes after
the lightning, so we can get away with such a deliberate mismatch.
> I think that's a recipe for trouble. Everyone knows what to do
> if audio & video are delay-matched at every component interface.
True, but overall it is not the easiest solution for all of us.
>>> If that system is embedded in the display and there is an A/V
>>> sync issue, I call that a major design flaw.
>> It is a flaw, but you tell me how to avoid it ?!
> Require audio loop-through, so you can delay audio appropriately.
But the point is: the majority of popular "home theater" type
of DVD players, what most people buy, do not have a loop-through
output ! They amplify their own audio directly. This fact
prohibits us from designing better video processing algorithms
if better implies a longer latency.
> An HDTV or EDTV set-top box should include a good deinterlacer,
> frame-rate conversion, any-format-in-any-format-out decoding &
> scaling, and again, should have audio & video delay-matched at
> its outputs.
We believe that the video enhancement processing power should be
in or near the display, not in every settop box or player.
But the fact is that the audio processing power has moved to the
DVD player (annex CD player, radio tuner, digital sound decoder,
audio amplifier, comes with small speakers and a subwoofer),
and this is why there we are now faced with lip sync problems.
Alan Roberts wrote:
> Lip sync loss is apparent to an experienced video man outside
> +30, -20mS, and to an experienced audio man outside +15, -5mS.
That may be, but I am more interested in what the relaxed and
untrained consumer will find acceptable (which is not the same
as noticeable). That range is NOT symmetrical around zero.
I see only one easy solution: the nominal delay difference
between video and audio should have been set in the middle of
the tolerance range (which may be -30 to +80 ms delay for
the audio, so set the audio to approx. +30 ms delay) instead
of zero. Zero is just an arbitrary number too...
Regards,
-- Jeroen.
|------------------------------+-----------------------------------------|
| From: Jeroen H. Stessen | E-mail: Jeroen.Stessen@xxxxxxxxxxx |
|------------------------------+-----------------------------------------|
| Building: SFJ-6.22 Eindhoven | Philips Digital Systems Laboratories |
|------------------------------+-----------------------------------------|
| Phone: ++31.40.27.32739 | P.O. Box 80002, (Street: Glaslaan 2) |
|------------------------------+-----------------------------------------|
| Fax: ++31.40.27.32572 | NL 5600 JB Eindhoven, the Netherlands |
|------------------------------+-----------------------------------------|
| Pager: ++31.6.6513.3818 | Visit us: http://www.pdsl.philips.com/ |
|------------------------------+-----------------------------------------|
----------------------------------------------------------------------
You can UNSUBSCRIBE from the OpenDTV list in two ways:
- Using the UNSUBSCRIBE command in your user configuration settings at
FreeLists.org
- By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word
unsubscribe in the subject line.
Other related posts:
