From: Ian Hoffenberg <[EMAIL PROTECTED]>
Subject: RE: Optimizing video quality with unique RealProducer settings
I don't think that changing the motion settings alters the frame rate that
the file is encoded at. I tried encoding 2 different streams, one with
"Smoothest Motion Video" and one with "Normal Motion Video" with all other
settings set to default and they both encoded at 15fps. The file set to
"Smoothest Motion Video" seemed to be better quality. I think it has
something to do with a change in the compression algorithm, but then again,
i'm not an engineer.
My question is this: Can you encode different streams at different window
sizes using Surestream technology, or must you encode them differently? It
would make my life much simpler to be able to encode just once using
different windows sizes for difference targeted audiences...
Thanks for the info...
Ian
-----Original Message-----
From: realforum [mailto:[EMAIL PROTECTED]]
Sent: Monday, December 06, 1999 1:37 PM
To: [EMAIL PROTECTED]
Subject: RE: Optimizing video quality with unique RealProducer settings
From: Helmut Hlavacs <[EMAIL PROTECTED]>
Subject: Re: Optimizing video quality with unique RealProducer settings
Hi Yvan!
RealForum wrote:
> From: "Yvan Gagnon" <[EMAIL PROTECTED]>
> Subject: Optimizing video quality with unique RealProducer settings
>
> I was wondering if anyone here might be willing to share their
> recommendations on what the ideal settings are for the encoding of
different
> bitrate realvideos. I've done quite a bit of research and experimenting,
> and I'm somewhat curious about certain things.
>
> Typically, I encode my realvideo files for 4 different bitrates: 28k,
56k,
> dual isdn, & DSL/Cable Modem. While analyzing the statistics of the some
of
> the videos created by encoding.com (who I've found get some pretty
> outstanding results) I noticed that they generally use the following
> settings:
>
> 28k - video : 160x120 - 6 fps | audio 6.5 kbps
> 56k - video : 176x132 - 6 fps | audio 8.5 kbps
> Dual ISDN - video : 240x180 - 12 fps | audio 8.5 kbps
> DSL/Cable Modem - video : 320x240 - 15 fps | audio 16 kbps
>
> Question #1 :
>
> If a Dual ISDN line can, in theory, handle something like 112 or 128
kbps,
> .. why use a bitrate of only 80 kbps? I'm noticing that this is also the
> default setting assigned in RealProducer, and I'm just wondering if this
> bitrate, -- and if all of these specific bitrates, -- were chosen for a
> specific reason, .. like to allow for overhead (web surfing, email, etc,
> ... ) or if there's a performance consideration of some sort. Why not
> encode at 100kbps?? Or higher even? I mean, . isn't an ISDN line
> dedicated?
According to information from the realsystem G2 production guide, section
"Choosing a target bandwidth", you only count on 75% of the total bandwidth
(2x56kbps*0.75 = 84 kbps).
The reason for this is that each packet carries significant overhead like
UDP packet header and SureStream Packet header. The 80kbps account
on the actual video and audio information data that is sent.
Also, other information is likely to be sent over the same connection,
though
not visible to you. Choosing 100% of the bitrate that can be sent over your
connection would not make much sense, as this cannot be kept constant
for all of the time. Also, after network congestions, the RealPlayer buffer
should be refilled once more, so you might temporarily need a higher bw.
>
>
> Question #2 :
>
> Obviously, the above settings can't always apply. For example, I had to
> encode a clip this afternoon that had lots of fast motion in it, and I
> couldn't help but notice that it looked like total shit at the lower
> bitrates (28k and 56k) . In these cases, meaning where there is lots of
> motion in the video to be encoded, what changes can I make to my settngs
to
> optimize clarity and at least get some half-decent looking results ??
The
> only thing that I've noticed makes a difference is when I change the
"Video
> Quality" setting to "Sharpest Image Video", .. though the change is
barely
> even noticeable.
I would try to set the fps to 1.5. This makes RealVideo to put more
picture information (-> better quality) into each frame.
>
>
> Question #3 :
>
> What are the actual differences between "Normal Motion Video", "Sharpest
> Image Video" and "Smoothest Motion Video" and when is it best to use each
??
I would suppose that
Sharpest Image Video chooses a better image quality and reduces the fps.
Smoothest Motion Video chooses a higher fps over image quality.
Normal Motion Video is somewhere in between.
Remember that the bits per second are kept constant, so RealVideo must
save bandwidth either in image quality or fps.
>
>
> Question #4 :
>
> I don't know if I'm just having some kind of technical problem or if
there's
> a bug in the new realplayer, .. but when I encode a video at 15 fps, and
> then monitor the statistics while playing the resulting realvideo file
> locally using realplayer, for some reason, the frame rate that it plays
back
> with is nowhere near what I encoded it at. For example, If I've
endcoded a
> realvideo file at 15fps, .. why is realplayer telling me that it's
playing
> back at only 6-7 fps --- locally ?? This is a PIII 500 w/ 256 mb ram
we're
> talking about here. Might this have anything to do with the fact that
the
> AVIs I'm encoding were originally captured at 15fps? Or should this not
> make any difference?
>
No idea, sorry.
Cheers
Helmut
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