Audio and Video Bitrate

[thesixuk]

I have a 700MB .AVI movie which I want to convert to DVD. Looking in GSpot for the file info I get the following:

Video Bitrate: 773 kb/s
Audio Bitrate: 116 kb/s

when I use the wizard in TMPGENC to start converting it, it suggests an audio bitrate of 384Kb/s (or something along those lines, I'm at work so I cant check right now)
Is there any point in increasing the bitrate to this level ifthe original .AVI is only 116Kb/s?

If I knocked down the audio bitrate to match the original would it improve the video quality of the final product?

[teegee420]

In my opinion, using an audio bitrate above 224kbps is never necessary but you don't want to go below 160. I would stick with 224, unless your ears can't distinguish a difference between 160 and 224. Even if you go with 160 the saved bitrate won't help the video quality significantly.

You didn't mention your avi's resolution so unless it's near 720x480 you shouldn't encode with that size. Enlarging the original movie's resolution too much often results in severe blockiness/pixelization. Consider using half D1, which is 352x480 and still a valid DVD resoulution.

[thesixuk]

the resolution's at 576x320. What would you do? at the moment i've encoded it to 720x480 and there is a little blockyness evident. however if i encoded it to 352x480 how would that affect the end result in terms of it's size on my screen?

[teegee420]

The size won't be affected. Your DVD player will stretch the frame to fill your TV.

[thesixuk]

So using that logic, if it's smaller than 720x480 wouldn't it always be better to size it down?

Thanks for your help so far teegee420 you've really helped a great deal.

[teegee420]

So using that logic, if it's smaller than 720x480 wouldn't it always be better to size it down?

In my opinion, yes. Anytime you enlarge a movie you are magnifying its flaws. Unless your source is absolutely perfect you're bound to end up with artifacts. Mpeg-4(divx/xvid) movie rips that fit on one or even two cd's are FAR from being flawless. I don't care how good they look.

Like anything else, there are sometimes exceptions. Take for example a movie like yours with a frame size of 576x320. If it was relatively short and you were able to use a video bitrate between 8000-9500kbps, it might look decent depending on the nature of the movie, i.e. the amount of fast-moving action. The longer the movie is though, the less bitrate you have to play with. Smaller bitrates are more efficiently spread over smaller frame sizes, making for a nicer looking movie.

Choosing to size down is a good rule of thumb, but nothing is absolute. Particularly with this hobby. If you are ever in doubt, run some short test clips to experiment and draw your own conclusions rather than listening to blow-hards like myself. Anyhow, good luck with your encoding and have fun.

[VCDHunter]

So using that logic, if it's smaller than 720x480 wouldn't it always be better to size it down?

Pretty much, enlarging say 352 x 288 to 720 x 480 will most likely produce some terrible results. Try it with small video clip.