Rendering an Xvid File to MPEG-2 for a DVD

[astrovideo]

I have an Xvid clip that's 232MB. I'd like to render it to a DVD-compatible MPEG-2 file so I can make a DVD out of it. I did an experiment, and it seems to work. The DVD plays in my home DVD player, and it looks fine.

My questions are:
1) Is this okay to do in terms of compatibility with other DVD players?
2) Does it make sense the resulting MPEG-2 file was about 3GB when the original Xvid file is only 232MB - How could the file "grow" if I am compressing it?

Here are the clip properties of the 2 files:

Original Xvid file - 232MB:
NTSC drop frame (29.97 fps)
Microsoft AVI files
24 bits, 640 x 480, 29.97 fps
Frame-based
XviD MPEG-4 Codec
Interleave audio for every 1 frames
MPEG Audio Layer3, 48.000 kHz, Stereo


After MPEG-2 (DVD-Compatible) compression -3GB:
NTSC drop frame (29.97 fps)
MPEG files
24 bits, 720 x 480, 29.97 fps
Lower Field First
(DVD-NTSC), 4:3
Video data rate: Variable (Max. 8000 kbps)
LPCM Audio, 48000 Hz, Stereo

Thank you.

[sjj1805]

Xvid is more highly compressed than MPEG2.
A 1 hour Xvid video occupies about 700MB
A 1 hour MPEG2 with a bit rate of 8000 is about 4GB.

[etech6355]

1) Is this okay to do in terms of compatibility with other DVD players?

The compatibiltiy would be the type of dvd used. Ex: A dvd-r versus a dvd+r. Some dvd players do not play dvd+r dvd's and don't like certain dvd-r dvd's. Best bet is use a dvd-r disk.

2) Does it make sense the resulting MPEG-2 file was about 3GB when the original Xvid file is only 232MB - How could the file "grow" if I am compressing it?

Your not compressing the Xvid file, your uncompressing it, Xvid uses more compression than mpeg2 which is used on dvd-video disks. This is normal.

[DVDDoug]

A couple more comments....

The file size in any format is determined by the combined audio & video bitrate and the playing time. Bitrate is usually expressed in kbps (kilobits per second). Sometimes you will see it expressed in Mbps. You can see how kilobits per second can fairly easily be converted to Gigabytes per hour. But, it's easier to use a Bitrate Calculator.

All of these video compression schemes use lossy compression. Data is thrown-away during compression. With a given format, a lower bitrate (smaller file) means that more data is being thrown-away, which leads to lower quality.

Xvid uses MPEG-4 compression which is more efficient (smarter) than MPEG-2 compression. A 2000kbps Xvid file should look better than a 2000kbps MPEG-2 file.

The quality is degraded wenever you convert from one lossy format to another. This is because the file is first decompressed and then another lossy compression step is performed. (If you use a high bitrate, the quality loss might not be noticeable.) Edits such as transitions or cropping also require the video to be decompressed and re-compressed. (The MPEG formats were not originally designed to be edited or converted.)

You also loose quality when you change the resolution or framerate. (In your case, the framerate was not changed.) When the 640x480 image is converted to 720x480 (as required by the DVD spec) additional pixels have to be generated to fill-in the gaps, and the original pixels have to be moved and adjusted (interpolated).