11.5+ rendering question

[GrandMasterPixel]

When I render a MPEG video twice using the same settings, each of the rendered video files differ in size. Why is this?

[Trevor Andrew]

Hi

If you use the same settings the file size should be the same.

What are the Project Properties?
What settings/template are you using for the render (Share Create Video File)?

Can you describe your workflow in more detail.?

[GrandMasterPixel]

I load a movie onto the time line, then create a video with custom settings.

I use:

MPEG files
24 bits, 720 x 576, 25 fps
Upper Field First
(MPEG-2), 16:9
Video data rate: Variable (Max. 9600 kbps)
Audio data rate: 384 kbps
MPEG audio layer 2, 44.1 KHz, Stereo

I save 1.mpg, it renders, complete.
I save 2.mpg, it renders, complete.

1.mpg & 2.mpg differ in file size, despite using the same settings. Why is this happening?

[sjj1805]

Every time you re-render an MPEG2 file its size WILL get smaller.
That is normal and that is why I published this post.

[GrandMasterPixel]

1.mpg & 2.mpg are both renders of 0.mpg.

1.mpg & 2.mpg were rendered with the same settings.

1.mpg & 2.mpg differ in file size.

Logic states 1.mpg & 2.mpg should be identical, yet they are not.

[Ken Berry]

So you don't render 0.mpg to 1.mpg, and then render 1.mpg to 2.mpg?

Can you tell us the size of the three files, please?

[GrandMasterPixel]

A. I place 0.mpg onto the time line.

B. I create a video file with the following custom settings and save it as 1.mpg:

MPEG files
24 bits, 720 x 576, 25 fps
Upper Field First
(MPEG-2), 16:9
Video data rate: Variable (Max. 9600 kbps)
Audio data rate: 384 kbps
MPEG audio layer 2, 44.1 KHz, Stereo

C. I now repeat B., only I save the file as 2.mpg.

0.mpg = 260 876 KB
1.mpg = 265 498 KB
2.mpg = 262 138 KB

Why are 1.mpg & 2.mpg different in size when they were rendered with exactly the same settings and from the same source (0.mpg)?

[Trevor Andrew]

Hi

I think this may be related to Smart Render.
Did you notice how much faster the 2.mpeg rendered.?

Repeat the process but continue to create a further 3.Mpeg
You may find this is the same as 2.mpeg

Otherwise disable smart render for each ender.
or

close open the project before creating 2.mpeg.

[GrandMasterPixel]

1.mpg & 2.mpg were rendered without SmartRender.

[Trevor Andrew]

Hi
First using a video file to your settings I allowed VS to match the project properties.
The file was only 52Mb a little smaller than yours, but seemed to produce these strange file sizes.

I then rendered the video to Same as Project Settings.

Using Smart Render gave me consistent file sizes, I repeated the render 4 times and each case gave me the exact same file sizes.

However rendering the video with Smart Render disabled was a different story.
Each video file was a different size.
Some smaller and some a little larger, nothing consistent.
I repeated the render 6 times, each case produced a different size.

I don’t have an explanation………..

I generally leave Smart Render enabled so haven’t noticed this before.

[GrandMasterPixel]

Hmmm. It seems I've found a bug then. With thanks to your work around however, the bug shouldn't effect me.

Does SmartRender produce better quality video's or less quality?

[Ken Berry]

With standard definition videos, SmartRender will usually produce better videos overall since in effect only those parts of the original video which you have edited are rendered. Since mpeg-2 -- the format required for DVDs -- and just about all other video formats are lossy in one way or another, this means that each time you render, you lose a little bit of quality. So by *not* rendering the parts of your video which have not been edited (which is what SmartRender does), you are preserving the original, higher quality in most of the video. Since a lot of the original video is not being rendered, it also means the time taken to produce your final product can be significantly reduced.

Note, however, that the the degree of loss of quality is fairly minute, and only becomes evident to the naked eye if you re-render several times or the quality of the original video was pretty poor to begin with. Note also that that SmartRender, with high definition video, appears to introduce various unwelcome artifacts into the finished product. I recommend that people not use it with either HDV or AVCHD as a result -- though I confess I am usually ignored!!