Question about generational quality loss in digital editing.

[Guest]

Archived from groups: rec.video.desktop (More info?)

Greetings, I have a question or three, that i hope might find an
answer.

What is the rule of thumb regarding quality loss when changing codecs
from say a DIVX to SVCD ?

I was under the impression that whenever you change codecs you
introduce artifacts and lower your quality regardless of the bitrates.

Now I have someone telling me that if you have say an AVI with an
extremely high bit rate, and then convert to say an MPEG at a lower
bit rate, you wont lose any additional quality.

Is this true? Like I said, i thought you always introduced problems
going from one codec to another.


Rob

 

[Guest]

Archived from groups: rec.video.desktop (More info?)

Rob Findlay wrote:

> Greetings, I have a question or three, that i hope might find an
> answer.
>
> What is the rule of thumb regarding quality loss when changing codecs
> from say a DIVX to SVCD ?
>
> I was under the impression that whenever you change codecs you
> introduce artifacts and lower your quality regardless of the bitrates.
>
> Now I have someone telling me that if you have say an AVI with an
> extremely high bit rate, and then convert to say an MPEG at a lower
> bit rate, you wont lose any additional quality.
>
> Is this true? Like I said, i thought you always introduced problems
> going from one codec to another.
>
> Rob

It's true that you'll lose quality - the question is whether or not you'll
notice it.

If you're going from "extremely high bit rate" AVI to say, high bit rate
mpeg-2, and play it back on a DVD player, you might or might not notice a
quality loss.

 

[Brian]

Archived from groups: rec.video.desktop (More info?)

spamfree@robfindlay.org (Rob Findlay) wrote:

>Greetings, I have a question or three, that i hope might find an
>answer.
>
>What is the rule of thumb regarding quality loss when changing codecs
>from say a DIVX to SVCD ?
>
>I was under the impression that whenever you change codecs you
>introduce artifacts and lower your quality regardless of the bitrates.
>
>Now I have someone telling me that if you have say an AVI with an
>extremely high bit rate, and then convert to say an MPEG at a lower
>bit rate, you wont lose any additional quality.
>
>Is this true? Like I said, i thought you always introduced problems
>going from one codec to another.
>
>
>Rob

You will always lose video quality when lowing the video bit rate. It
can depend of the type of video. If there is a lot of movement or
camera panning then lowering the bit rate can result in some picture
interference.
If the video source is of high quality and has a high bit rate then
lowing the bitrate to about 8000 kps mpg will still give you a good
picture.

Regards Brian

 

[Rio]

Archived from groups: rec.video.desktop (More info?)

> You will always lose video quality when lowing the video bit rate. It
> can depend of the type of video. If there is a lot of movement or
> camera panning then lowering the bit rate can result in some picture
> interference.
> If the video source is of high quality and has a high bit rate then
> lowing the bitrate to about 8000 kps mpg will still give you a good
> picture.


Most video codecs are LOSSY, this means you loose quality (some
informations) during the conversion... even a still image looses quality if
you encode it lot of times....
Try to use always an uncompressed/lossless format to keep the original
quality and convert to the final lossy format at the very last step...

--
rIO.sK