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Penster
Guest
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 Posted:
Sun Oct 02, 2005 5:54 pm Post subject:
Improving low bitrate Divx |
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I make Divx programs to watch on a palm handheld. I convert PAL TV programs
from a hard disk recorder. I convert using VirtualdubMPEG2. They are 480x320
250 kbps using 2 pass Divx with mono sound. I use 12.5 framerate.
Generally I am satisfied with the results, but the main annoying artefact
occurs when the picture is of a slab of gently graded colour, such as a blue
sky, where the colour tends to seperate into blocks with a distinct boundary
between colour changes.
Is there any way to lessen the effect, eg by use of a filter? Any advice
gratefully received.
Penster
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Jan Panteltje
Guest
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| Posted:
Sun Oct 02, 2005 8:07 pm Post subject:
Re: Improving low bitrate Divx |
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On a sunny day (Sun, 02 Oct 2005 12:54:40 GMT) it happened "Penster"
<xxx@xxx.com> wrote in <kMQ%e.608$rp1.494@newsfe4-win.ntli.net>:
| Quote: | I make Divx programs to watch on a palm handheld. I convert PAL TV programs
from a hard disk recorder. I convert using VirtualdubMPEG2. They are 480x320
250 kbps using 2 pass Divx with mono sound. I use 12.5 framerate.
Generally I am satisfied with the results, but the main annoying artefact
occurs when the picture is of a slab of gently graded colour, such as a blue
sky, where the colour tends to seperate into blocks with a distinct boundary
between colour changes.
Is there any way to lessen the effect, eg by use of a filter? Any advice
gratefully received.
Penster
This is likely a color depth problem, perhaps the Palm does not have true color |
video, but only 16 or more colors.
Are thse movies OK on the PC?
If so it is the palm colordepth likely.
Nothing you can do about that. |
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Penster
Guest
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| Posted:
Sun Oct 02, 2005 10:13 pm Post subject:
Re: Improving low bitrate Divx |
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| Quote: | This is likely a color depth problem, perhaps the Palm does not have true
color
video, but only 16 or more colors.
Are thse movies OK on the PC?
If so it is the palm colordepth likely.
Nothing you can do about that.
The effect also occurs on the PC. My guess is that it is blocking due to the |
low bitrate, which is most noticable when looking at slabs of colour.
Penster |
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Jan Panteltje
Guest
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| Posted:
Sun Oct 02, 2005 10:57 pm Post subject:
Re: Improving low bitrate Divx |
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On a sunny day (Sun, 02 Oct 2005 17:13:56 GMT) it happened "Penster"
<xxx@xxx.com> wrote in <ozU%e.7353$0f3.2994@newsfe1-win.ntli.net>:
| Quote: | This is likely a color depth problem, perhaps the Palm does not have true
color
video, but only 16 or more colors.
Are thse movies OK on the PC?
If so it is the palm colordepth likely.
Nothing you can do about that.
The effect also occurs on the PC. My guess is that it is blocking due to the
low bitrate, which is most noticable when looking at slabs of colour.
Penster
Ah yes, those are square blocks? |
If so it is indeed a bitrate problem.
On the other hand 240kbps on 480x320@15fps should be OK on DivX.
(lemme see I use full PAL at 1500kbps 720x576@25 = 10368000 pixels / second
You use 240kbps 460x320@15 = 2304000 pixels / second
1500 / 240 = 6.25
10368000 / 2304000 = 4.5
Try 1500 / 4.5 = 333kbps.....
But really, 240 should be OK, I have used lower then 1500 too.
Other things to look for is noise in the source material, maybe use a noise
filer (low pass)?
Lots of noise will make compression more difficult.
All I know :-) |
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Penster
Guest
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| Posted:
Mon Oct 03, 2005 12:53 am Post subject:
Re: Improving low bitrate Divx |
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Jan
Thanks for the advice. I am really trying to squeeze the maximum quality out
of the minimum bitrate. I get 1 hour of viewing on 120 MB stored on an SD
card. As the bitrate goes up it also challenges the Palm 400MHz processor.
While I am picking your brains, can I ask about Divx 2 pass. I use 250 for
the second pass, but I read somewhere that I should use a higher bitrate for
the first pass so I use 2000. Is there a setting for the first pass bitrate
which will give the best results?
Penster
"Jan Panteltje" <pNaonStpealmtje@yahoo.com> wrote in message
news:1128275864.cc0260cb6f77588f7b6a98a66716dac1@teranews...
| Quote: | On a sunny day (Sun, 02 Oct 2005 17:13:56 GMT) it happened "Penster"
xxx@xxx.com> wrote in <ozU%e.7353$0f3.2994@newsfe1-win.ntli.net>:
This is likely a color depth problem, perhaps the Palm does not have
true
color
video, but only 16 or more colors.
Are thse movies OK on the PC?
If so it is the palm colordepth likely.
Nothing you can do about that.
The effect also occurs on the PC. My guess is that it is blocking due to
the
low bitrate, which is most noticable when looking at slabs of colour.
Penster
Ah yes, those are square blocks?
If so it is indeed a bitrate problem.
On the other hand 240kbps on 480x320@15fps should be OK on DivX.
(lemme see I use full PAL at 1500kbps 720x576@25 = 10368000 pixels /
second
You use 240kbps 460x320@15 = 2304000 pixels /
second
1500 / 240 = 6.25
10368000 / 2304000 = 4.5
Try 1500 / 4.5 = 333kbps.....
But really, 240 should be OK, I have used lower then 1500 too.
Other things to look for is noise in the source material, maybe use a
noise
filer (low pass)?
Lots of noise will make compression more difficult.
All I know :-) |
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Jan Panteltje
Guest
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| Posted:
Mon Oct 03, 2005 2:20 am Post subject:
Re: Improving low bitrate Divx |
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On a sunny day (Sun, 02 Oct 2005 19:53:25 GMT) it happened "Penster"
<xxx@xxx.com> wrote in <VUW%e.11840$DO.425@newsfe3-gui.ntli.net>:
| Quote: | Jan
Thanks for the advice. I am really trying to squeeze the maximum quality out
of the minimum bitrate. I get 1 hour of viewing on 120 MB stored on an SD
card. As the bitrate goes up it also challenges the Palm 400MHz processor.
While I am picking your brains, can I ask about Divx 2 pass. I use 250 for
the second pass, but I read somewhere that I should use a higher bitrate for
the first pass so I use 2000. Is there a setting for the first pass bitrate
which will give the best results?
Hi, good question. |
I always use 2 pass, and always simply specify the same bitrate for pass one
as pass two.
The intention of the first pass is to make a list of parameters for each frame
that tells the encoder how best to compress it.
I am not sure if and how the bitrate you specify in the first pass is used
in the calculation, somebody from the Xvid project should really answere this.
But if it is used then I think better use the same bitrate for both passes, if
it is not used then it makes no difference.
I had (it came with very first DivX codec many years ago) a text file that
explained things, but nowadays I use fixed scripts (that I made in those days)
with Linux transcode.
These use the same bitrate and work very well.
So that is what I recommend you do :-) |
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Penster
Guest
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| Posted:
Mon Oct 03, 2005 4:40 am Post subject:
Re: Improving low bitrate Divx |
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Jan
Thanks for the reply.
Penster
"Jan Panteltje" <pNaonStpealmtje@yahoo.com> wrote in message
news:1128288031.bbadc3d0d5474813fe9801422639642c@teranews...
| Quote: | On a sunny day (Sun, 02 Oct 2005 19:53:25 GMT) it happened "Penster"
xxx@xxx.com> wrote in <VUW%e.11840$DO.425@newsfe3-gui.ntli.net>:
Jan
Thanks for the advice. I am really trying to squeeze the maximum quality
out
of the minimum bitrate. I get 1 hour of viewing on 120 MB stored on an SD
card. As the bitrate goes up it also challenges the Palm 400MHz
processor.
While I am picking your brains, can I ask about Divx 2 pass. I use 250
for
the second pass, but I read somewhere that I should use a higher bitrate
for
the first pass so I use 2000. Is there a setting for the first pass
bitrate
which will give the best results?
Hi, good question.
I always use 2 pass, and always simply specify the same bitrate for pass
one
as pass two.
The intention of the first pass is to make a list of parameters for each
frame
that tells the encoder how best to compress it.
I am not sure if and how the bitrate you specify in the first pass is used
in the calculation, somebody from the Xvid project should really answere
this.
But if it is used then I think better use the same bitrate for both
passes, if
it is not used then it makes no difference.
I had (it came with very first DivX codec many years ago) a text file that
explained things, but nowadays I use fixed scripts (that I made in those
days)
with Linux transcode.
These use the same bitrate and work very well.
So that is what I recommend you do :-) |
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