Adjusting filesizes of highly compressable movies

[seoulsteve]

I'm sure that more that a few people here have problems with undersized files using the 5.02Pro codec. I encoded Enemy atthe Gates over the weekend and was consistently getting undersized files. Hate that!

I tried various combinations of resolution, bitrate, audio sizes and finally, after four encodes, got my 700MB. Totally frustrating!

What I'd like to know is....

How does resolution affect file size? Obviously bigger resolutions elicit bigger file sizes, but is there a way to mathematically figure out the final file size based on a given bitrate and resolution?

Usually I just fiddle with bitrate if the file size is an issue, but with the 5.02Pro codec sometimes it doesn't need as many bits as you give it to encode at a certain resolution. Thus smaller than desired file sizes.

I've read the sticky notes and used search to find answers, but still am unclear. Is there an easy formula to follow?

[Mac Sidewinder]

How does resolution affect file size? Obviously bigger resolutions elicit bigger file sizes, but is there a way to mathematically figure out the final file size based on a given bitrate and resolution?

Resolution doesn't affect filesize. Your bitrate determines this. Basically when you set bitrate, that many bits are distributed into whatever resolution size you set. So the higher the res, the lower number of bits are distributed for each frame. Unless you use a very high bitrate, you will notice lower quality the higher res you go.

If you are getting undersized files because of a highly compressable movie - try the following:

turn off b-frame usage
encode 1 pass 100% quality
turn off all divx 5 mpeg extras

if you still get undersized files don't sweat it - your movie is at max quality. Use the extra space to beef up the audio instead.

See the sticky in this forum for more info on undersized files

Mac

[DJ Bobo]

Just a small correction: resolution DOES have influence on size, IF you encode in quality based mode. The bigger the resolution, the bigger the bitrate, the bigger the size.

When you get undersized files, it's like you were encoding in quality based 100% mode: "perfect" quality! ;)

[EDIT]
You may define it that way: when you reach the desired size, the quality isn't optimal. When you get an undersized file, your rip is perfect!

[seoulsteve]

Just a small correction: resolution DOES have influence on size

I thought so.:)

Am I wrong in thinking that a 500MB "100% perfect quality" encode has less quality than a 700MB "perfect" encode? I think not, but I've been wrong before.:rolleyes:

My theory in all this is to mathematically figure out the "perfect 100% quality" encode at 700MB. It stands to reason that if a bitrate of .250 and a resolution of 672X288 ellicit a file size of 500MB, even though file size is set at 700MB, then a combination of a higher bitrate and larger resolution would give you a more detailed "perfect quality" picture.

I want to use the 5.02Pro codec to its fullest and don't want to omit any/all of the codec's extras. Quality is my concern, not filesize.

Is there a way to find this elusive perfect combination of bitrate and resolution?

[hakko504]

Originally posted by seoulsteve

Am I wrong in thinking that a 500MB "100% perfect quality" encode has less quality than a 700MB "perfect" encode? I think not, but I've been wrong before.:rolleyes:
That depends on what movies you are comparing. At the same resolution, I'd say that most of the time the 500MB perfect encode is the one that is most eye pleasing, but this may also depend on what filtering you have done.
It stands to reason that if a bitrate of .250 and a resolution of 672X288 ellicit a file size of 500MB, even though file size is set at 700MB, then a combination of a higher bitrate and larger resolution would give you a more detailed "perfect quality" picture.
Yes, but you can't do magic. That is, you only gain details when you compare resolutions LOWER than your original DVD resolution (720x480/576).
I want to use the 5.02Pro codec to its fullest and don't want to omit any/all of the codec's extras. Quality is my concern, not filesize.
Remember that all extras do not make a better picture in all cases. You might need to turn GMC and psychovisuals on and off and re-encode several times to get the optimal choise for a give film.
Is there a way to find this elusive perfect combination of bitrate and resolution?
Yes, it's called re-encoding. Compression tests will help, but they are unreliable if you use B-frames. Normally wou will get undersized files when the compression test (in GKnot) shows about 75-85%. So if you make a series of compression test, then you can easily skip resolution/filter combos with lower value than 75%, and the start encoding your way up in the compression test results until you get perfection.

[Mac Sidewinder]

I want to use the 5.02Pro codec to its fullest and don't want to omit any/all of the codec's extras. Quality is my concern, not filesize.

Is there a way to find this elusive perfect combination of bitrate and resolution?

My response above was in reference to doing a 2 pass encode and trying to reach a specified filesize.

If size doesn't matter then would a single pass 100% WITHOUT any divx 5 extras turned on be the best you can get?

Mac

[Acaila]

If size doesn't matter then would a single pass 100% WITHOUT any divx 5 extras turned on be the best you can get?
Yes.

Provided the resolution is high enough ofcourse.

[Mac Sidewinder]

@Acaila - thats what I thought - of course if you was trying to get the "best" possible encode quality without worrying about filesize - you'd use the highest resolution without going above the original size (740x). correct?

Mac

[hakko504]

Originally posted by Mac Sidewinder
@Acaila - thats what I thought - of course if you was trying to get the "best" possible encode quality without worrying about filesize - you'd use the highest resolution without going above the original size (740x). correct?Yes! :)