pixelation?

[megalith6]

hi,

from the eternal newb

why do my MPEG's sometimes contain big pixels - is this also known 'pixelation'?

can you take an MPEG or AVI file created within a commercial software programme, and 'tweak' it / customise it yourself, with something like AviSynth?

mucky edges - :eek: - is there a software which will allow you to crop out blury edges?

:thanks:

Ric

[Adub]

It's actually called blocking, and the reason it occurs is due to high compression. It runs out of bits to fill that "block" and so it ends up just kind of flattening out. Other people should be able to tell you more as to why it happens.

[megalith6]

It's actually called blocking, and the reason it occurs is due to high compression. It runs out of bits to fill that "block" and so it ends up just kind of flattening out. Other people should be able to tell you more as to why it happens.

thanks Merlin

that gets me further on down the line of enquiry :)

wondered if swopping between MPEG formats or alternative encoders (codices?) might help - which probably shows how little i know about the subject :scared:

can also never understand why some web videos look 'smooth' whilst others tend to 'blocking' ~ there has to be a simple straightforward explanation for this, but i have never seen it aired

thanks again

Ric

[poisondeathray]

A common cause is not enough bitrate. Even MPEG2 will be less likely to exhibit blocking if you throw enough bitrate at it

AVC/h.264 features inloop deblocking, so you rarely get pixellation even at very low bitrates. Early implementations caused "oversmoothing" and loss of detail. If you use one of the newer x264 builds with new features, there is a trend towards recovering the lost detail

You can crop edges only by re-encoding the video. When you re-encode video using a lossy codec it only makes the quality worse.

If your source material already has pixellation (i.e. poor quality), you can rarely improve upon it.

You should always start with the highest quality source (e.g. blu-ray, or DVD)

EDIT: if it's just for playback purposes, you can use an avisynth script in playback to crop the edges without altering the original video

[megalith6]

A common cause is not enough bitrate. Even MPEG2 will be less likely to exhibit blocking if you throw enough bitrate at it

AVC/h.264 features inloop deblocking, so you rarely get pixellation even at very low bitrates. Early implementations caused "oversmoothing" and loss of detail. If you use one of the newer x264 builds with new features, there is a trend towards recovering the lost detail

would this fit the bill?

http://www.coreavc.com/

You can crop edges only by re-encoding the video. When you re-encode video using a lossy codec it only makes the quality worse.

If your source material already has pixellation (i.e. poor quality), you can rarely improve upon it.

You should always start with the highest quality source (e.g. blu-ray, or DVD)

usually Firewire a capture direct to edit software and convert to mpeg (mpeg2?) or avi when i want to share a clip, or dvd quality when i want to burn a disc; the mpeg and avi files suffer most from pixel blocking and i wonder if my old encoders might also not be helping matters (Pinnacle 9 AV/DV)?

EDIT: if it's just for playback purposes, you can use an avisynth script in playback to crop the edges without altering the original video

this is something i must experiment with

thanks

R

[poisondeathray]

would this fit the bill?

http://www.coreavc.com/




That is an AVC decoder, not an encoder. There are free alternatives like ffdshow to decode AVC content

(it's only $15 for the pro version but well worth it IMO)




usually Firewire a capture direct to edit software and convert to mpeg (mpeg2?) or avi when i want to share a clip, or dvd quality when i want to burn a disc; the mpeg and avi files suffer most from pixel blocking and i wonder if my old encoders might also not be helping matters (Pinnacle 9 AV/DV)?



.avi is just a container. It might contain XviD video or wmv9, for example. If you use enough bitrate, it should reduce the pixellation, so try and tinker with your settings

(although h264 is more efficient - i.e. higher compression but takes more CPU power. You get same or better quality at lower bitrates than XviD or MPEG2)

[megalith6]

That is an AVC decoder, not an encoder. There are free alternatives like ffdshow to decode AVC content

(it's only $15 for the pro version but well worth it IMO)

coreavc looks good enough to eat


.avi is just a container. It might contain XviD video or wmv9, for example. If you use enough bitrate, it should reduce the pixellation, so try and tinker with your settings

[thinks] i need some sort of interface to 'read' files - so i can see what they actually are

(although h264 is more efficient - i.e. higher compression but takes more CPU power. You get same or better quality at lower bitrates than XviD or MPEG2)

how do you author lower bitrate files please?

thanks

Ric

[poisondeathray]

[thinks] i need some sort of interface to 'read' files - so i can see what they actually are



You can use mediainfo (view=>text)




how do you author lower bitrate files please?



You can choose whatever settings you want. I'm unclear on what your question is?

[megalith6]

You can use mediainfo (view=>text)

oh my goodness you mean this?

http://mediainfo.sourceforge.net/en

which looks amazing :eek:


You can choose whatever settings you want. I'm unclear on what your question is?

say i have an avi-type file and i want to reduce its biterate, what would be a basic way to achieve this - in order to reduce pixel 'blocking', for example?

many thanks

R