IPB

Welcome Guest ( Log In | Register )

Can audio encoders target quality w/o caring about bit rate/file size?, [OP = softrunner / split from “IETF Opus codec now ready for testing”]
softrunner
post Feb 14 2013, 02:33
Post #1





Group: Members
Posts: 48
Joined: 19-July 12
Member No.: 101579



QUOTE (Martel @ Jan 1 2013, 14:46) *
QUOTE (softrunner @ Dec 29 2012, 04:50) *
I don't know weather it is possible for encoder to do such an analysis of a source audio, but it would be great it yes.
It's only a matter of finding the right formula/algorithm.

x264 video encoder has encoding mode called Constant Rate Factor. In this mode number (16, 17, etc) is used to define desired quality (lower - better quality and higher bitrate), and encoder does not care about bitrate, only about keeping rate factor constant. It is a question, why nobody has invented something similar for audio encoding (except lossyWAV, which needs too much bitrate for acceptable quality)?
----------------
Opus 1.1 Alpha has some bugs, which can be found using samples from thread High Frequency Listening Test Samples. For example, at 16-24 kbps Opus gives this:

and for 32-40 kbps it gives this:

For samples 1_12kHz, 1_20kHz, 2_8kHz, 2_12kHz and 2_20kHz Opus sounds wrongly even at 512 kbps.
Full set of files is here (problematic sampes are marked with exclamation mark). Hope, developers will use this samples in their work.

This post has been edited by softrunner: Feb 14 2013, 02:34
Go to the top of the page
+Quote Post
 
Start new topic
Replies
Big_Berny
post Feb 14 2013, 12:11
Post #2





Group: Members
Posts: 242
Joined: 9-February 03
Member No.: 4921



QUOTE (softrunner @ Feb 14 2013, 02:33) *
x264 video encoder has encoding mode called Constant Rate Factor. In this mode number (16, 17, etc) is used to define desired quality (lower - better quality and higher bitrate), and encoder does not care about bitrate, only about keeping rate factor constant. It is a question, why nobody has invented something similar for audio encoding (except lossyWAV, which needs too much bitrate for acceptable quality)?

I think every encoder with real vbr (not abr) does that? Lame has V(0-9), QT AAC has --tvbr (0-127), Vorbis has -q((-2)-10). The bitrate may vary a lot with these settings between different songs/genres.
Go to the top of the page
+Quote Post
IgorC
post Feb 17 2013, 02:22
Post #3





Group: Members
Posts: 1533
Joined: 3-January 05
From: ARG/RUS
Member No.: 18803



Speech isn't that easy to code. http://research.nokia.com/files/public/%5B..._Opus_Codec.pdf

Opus uses hybrid mode only at very low bitrates. Speech requires comparable bitrate as for music for (near) transparent or high quality . There is no such thing as smart encoder that does"64 kbps for speech and 128 kbps for music".
That's enough to say that Opus 1.1 alpha (--bitrate 64) produces bitrates considerably >64 kbps on speech. It doesn't go anyhow lower.
Go to the top of the page
+Quote Post
db1989
post Feb 17 2013, 03:15
Post #4





Group: Super Moderator
Posts: 5275
Joined: 23-June 06
Member No.: 32180



QUOTE (IgorC @ Feb 17 2013, 01:22) *
Speech isn't that easy to code. http://research.nokia.com/files/public/%5B..._Opus_Codec.pdf […] Speech requires comparable bitrate as for music for (near) transparent or high quality .
Thanks for this! It supports earlier suppositions that bitrates for speech that are similar to music point to speech being more complex than we estimate, not to any failing in VBR modes.

I guess we’re conditioned to think of speech as requiring low bitrates, when in fact it’s often just a case of people forcing low bitrates due to constraints upon bandwidth or capacity, or even just habit. I can appreciate that actually encoding speech at a level that matches music may be more of a challenge than is assumed. That was the case for me, anyway. smile.gif
Go to the top of the page
+Quote Post

Posts in this topic


Reply to this topicStart new topic
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:

 



RSS Lo-Fi Version Time is now: 25th July 2014 - 20:12