(aac) higher bitrate AND smaller filesize ?!
So, i did at test the other day.
I tried to convert the same song (eminem feat dido - Stan) from wave with varius aac option. I used QT6.4 and nero's encoder.
So with QT i made a 128kbps and a 160kbsp version of the song, and with nero i used the preset option extreme (upto 190kbps i think) and transparent (upto 160kbps). I also did a LAME --aps.
Afterward i checked the size of the files. The funny thing was that the 128kbps (by QT6.4) was bigger then the transparent. I then used the mp4info tool from rareware to check the bitrate. The aac transparent preset hat like 15-20kbps (as far as i remember), but still the filesize was smaller. Now i dont get this.
How can a file with a higher bitrate have a smaller files then a file with lower bitrate !?
[785 byte] By [
pank2002] at [2007-11-9 15:41:58]
# 2 Re: (aac) higher bitrate AND smaller filesize ?!
Im not sure you understand me.
I made two files: 1 CBR (128kbps) with QT6.4 and one VBR (~134kbps) with transparetn preset in nero.
So the VBR file have a higher average bitrate per seconds then the file made with QT, and sill the nero VBR file is smaller.
Now, how can the QT aac file with smaller bitrate, have a bigger file size ?
# 3 Re: (aac) higher bitrate AND smaller filesize ?!
Adam had it right.
First, the difference in file size between a CBR 128 and a CBR 135 is very small to begin with. YES I am comparing CBR to CBR in this sentence.
Using CBR means a constant bit rate is used regardless of the information in the music. That means a file of complete silence and a file of screaming metal will have the same file size if they are the same length.
VBR means that the algorithm constantly checks the db level of the input and if there is nothing or low amounts music it adjusts the bit rate to a lower rate for that period to save file size.
You are comparing two rates (128 to 135) that if both were CBR they would be very similar in size to begin with, make the 135 a VBR and it will be smaller that the CBR.
The reason you would use VBR is to get a higher bitrate quality song for the same size as a smaller constant bitrate song.
128 CBR and 160 VBR should be about the same.
That said, you give up control of the quality of the bitrate to an algorithm, assuming its making the best judgement for you. If your music is filled with peaks and valleys of music then you may have poorer quality due to clipping, but hey you'll save space.
-Rich
# 4 Re: (aac) higher bitrate AND smaller filesize ?!
Thanks rich. Knew it before you told me though.
The file which i created with nero (transparetn preset) have an *average* bitrate at 135kbps (data from mp4info). Now when the average bitrate is higher on the VBR file the file size *should* be bigger to, ey?
However it isnt... Apple gotta have some chucnk of data in
# 5 Re: (aac) higher bitrate AND smaller filesize ?!
Originally posted by pank2002
Thanks rich. Knew it before you told me though.
The file which i created with nero (transparetn preset) have an *average* bitrate at 135kbps (data from mp4info). Now when the average bitrate is higher on the VBR file the file size *should* be bigger to, ey?
However it isnt... Apple gotta have some chucnk of data in
Somewhere something is goofing up. If that tool of yours is right, then multiplying the length of the song (in seconds) times the bitrate it gives and then dividing by 8 should give the file size reported in windows.
Does it?
