Skip to main content ↑ ↓

Notice

Please note that most of the software linked on this forum is likely to be safe to use. If you are unsure, feel free to ask in the relevant topics, or send a private message to an administrator or moderator. To help curb the problems of false positives, or in the event that you do find actual malware, you can contribute through the article linked here.
Topic: How does Quicktime ABR work? (Read 5616 times) previous topic - next topic
0 Members and 1 Guest are viewing this topic.

How does Quicktime ABR work?

When I encode a musicsample with Nero in 128kb/s CBR then the average bitrate is not exactly 128kb/s (which is normal as it uses ABR).

When I encode the same sample with Quicktime 128kb/s CBR then the bitrate is exact 128kb/s although Quicktime 6.5 also uses ABR (as you can see while playing in Foobar2000).

Does quicktime use a 2-pass mode (like WMA)? Or does it just have a very flexible bit reservoir?

How does Quicktime ABR work?

Reply #1 –
I'm pretty sure its just plain CBR which is why you get a predicatable file size.

How does Quicktime ABR work?

Reply #2 –
I don´t think so, when I play the file with Foobar2000, the bitrate can go down to 100kb/s and go up to 180kb/s (VBR bitrate display = 1 frame), when I choose 128kb/s in iTunes.

How does Quicktime ABR work?

Reply #3 –
Quote
When I encode a musicsample with Nero in 128kb/s CBR then the average bitrate is not exactly 128kb/s (which is normal as it uses ABR).

Foobar2000 doesn't show the bitrate very presicely if the music sample is relatively short.
Also IIRC Nero's CBR mode is CBR according to the specs, not ABR -> the bit reservoir is something like 1-1.5 kB (don't remember exactly) which means it's "CBR" according to specs although it can fluctuate few kbps.
Juha Laaksonheimo

How does Quicktime ABR work?

Reply #4 –
I´ve encode the song "Wim Mertens - Struggle for pleasure" with a length of 4:01. Foobar shows that the average bitrate for 128kb/s Nero CBR = 124kb/s

When I encode with quicktime, the bitrate is shown as 128kb/s but looks rather ABR.

How does Quicktime ABR work?

Reply #5 –
Quote
I´ve encode the song "Wim Mertens - Struggle for pleasure" with a length of 4:01. Foobar shows that the average bitrate for 128kb/s Nero CBR = 124kb/s

When I encode with quicktime, the bitrate is shown as 128kb/s but looks rather ABR.

Better look a the file size. foobar2000 shows the bitrate of the aac stream, not the average bitrate of the file (stream and overhead, something like that). Take a look at the following discussion :

http://www.hydrogenaudio.org/forums/index....showtopic=16418

Or extract aac stream for you 128 kbps m4a files, and reconvert it in mp4. The same file is now 124 kbps, and not 128 kbps anymore

How does Quicktime ABR work?

Reply #6 –
Quote
I´ve encode the song "Wim Mertens - Struggle for pleasure" with a length of 4:01. Foobar shows that the average bitrate for 128kb/s Nero CBR = 124kb/s

When I encode with quicktime, the bitrate is shown as 128kb/s but looks rather ABR.

I think this has already been answered CBR+ bit resevoir can look like ABR if the resevoir is reasonabley large.

It's CBR.

Fairy

How does Quicktime ABR work?

Reply #7 –
Is it accurate to say that CBR->ABR->VBR is really just a continuum, and the distinction is the size of the bit resevoir?

How does Quicktime ABR work?

Reply #8 –
You can watch the bitrate changing, while playing your AAC-encoded files (iTunes) with WinAmp 5 (you need the plugin). 

Ciao