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Rockbox mail archiveSubject: Re: MPEG Audio formatRe: MPEG Audio format
From: Bluechip <csbluechip_at_gmail.com>
Date: Sat, 14 Jan 2006 19:37:48 +0000 I know this (and many similar/identical) documents well. This is my personal fave: http://www.codeproject.com/audio/MPEGAudioInfo.asp And I agree with "sounds like" ...it also sounds like you can change mpeg version, layer and samplerate ...in which case the statistical analysis of the audio data becomes a five (or was it six) dimentional array ...which is a cakewalk to process and a total nightmare to present to the user as something useful. So I need to try and reduce the level of complexity at a more lateral level - that is, the reultant program would whinge about the "probably legal but nobody actually has one" files in favour of being helpful the other 99% of the time. Hope that explains the background behind why I am asking core question: In reality, what do I atually have to deal with. BC At 06:52 14/01/2006, you wrote: >Okay, I was a little confused by the semantics. I think of "joint stereo" as >being MS (which stands for Mid/Side which means that instead of encoding >left and right you encode sum and difference). > >It looks like they have "stereo" mode which is simply pure stereo, and >"joint stereo" which means that you can add the additional features of >"Mid/Side" and "Intensity Stereo", but if you don't add either one then you >really have exactly the same thing as just "stereo". > >So, in the samples lame generates it switches on and off Mid/Side (and >probably would use "Intensity Stereo" at lower bitrates), but leaves the >high-level mode as "Joint Stereo" for all frames. However, in reading the >frame specification on this site it sounds like the high-level joint stereo >setting *can* be changed from frame to frame also: > >http://www.mp3-tech.org/programmer/frame_header.html > >Hope this makes some sense... :) > >David > >----- Original Message ----- >From: "Bluechip" <csbluechip_at_gmail.com> >To: <rockbox-dev_at_cool.haxx.se> >Sent: Friday, January 13, 2006 10:12 PM >Subject: Re: MPEG Audio format > > > > Whoops ...hit send a bit quick > > > > Nice of LAME to not update the frame counter when it completes. > > > > Meant to append this: > > > > D:\x>c:lame themic~1.wav > > LAME version 3.96.1 (http://lame.sourceforge.net/) > > CPU features: MMX (ASM used), 3DNow! (ASM used) > > Using polyphase lowpass filter, transition band: 10758 Hz - 11025 Hz > > Encoding The Microsoft Sound.wav to The Microsoft Sound.wav.mp3 > > Encoding as 22.05 kHz 64 kbps j-stereo MPEG-2 Layer III (11x) qval=3 > > Frame | CPU time/estim | REAL time/estim | play/CPU | >ETA > > 300/302 (99%)| 0:01/ 0:01| 0:02/ 0:02| 4.0816x| >0:00 > > average: 64.0 kbps LR: 83 (27.30%) MS: 221 (72.70%) > > > > Writing LAME Tag...done > > ReplayGain: -2.6dB > > > > > > _at_0x000000D0+0.0, 63529 - 304 MPEG audio frames > > | ,-- > > | | MPEG Version : MPEG Version 2 (ISO/IEC 13818-3) > > | | MPEG Layer : Layer III > > | | Samplerate : 22050 Hz > > | | Bitrate : CBR _at_ 64 KbpS > > | | Samples/Frame : 576 > > | | Frame Time : 26.122449 mS > > | | > > | | Frame Count : 304 -> 100.0% (of ALL frames) > > | | Frame Time : 0:00:07.941 > > | `-v > > | | (%'s below are for this block only) > > | | > > | +-- Channels : 304 -> 100.0% _at_ Joint Stereo [Xing index: 0] > > | | 83 -> 27.3% _at_ JS (only) > > | | 221 -> 72.7% _at_ JS +M/S > > | | > > | +-- Emphasis : 304 -> 100.0% _at_ No Emphasis > > | | > > | | --- Enabled ---- -+- --- Disabled --- > > | +-- Original : 304 -> 100.0% | 0 -> 0.0% > > | +-- Copyright : 0 -> 0.0% | 304 -> 100.0% > > | +-- Private : 0 -> 0.0% | 304 -> 100.0% > > | | | > > | +-- Protected : 0 -> 0.0% | 304 -> 100.0% > > | +-- Padding : 297 -> 97.7% | 7 -> 2.3% > > | | ^ > > | `-- Bitrate : CBR _at_ 64 KbpS > > `--------------------------------------------------------------------- > > > > > > >>I just ran lame with no options on the first file I found and got the > > >>following output: > > >>--------------- > > >>LAME version 3.96.1 (http://lame.sourceforge.net/) > > >>CPU features: MMX (ASM used), SSE, SSE2 > > >>Using polyphase lowpass filter, transition band: 17249 Hz - 17782 Hz > > >>Encoding concat.wav to concat.mp3 > > >>Encoding as 44.1 kHz 128 kbps j-stereo MPEG-1 Layer III (11x) qval=3 > > >> Frame | CPU time/estim | REAL time/estim | play/CPU | >ETA > > >> 2379/2381 (100%)| 0:09/ 0:09| 0:10/ 0:10| 6.2245x| >0:00 > > >>average: 128.0 kbps LR: 849 (35.64%) MS: 1533 (64.36%) > > >> > > >>Writing LAME Tag...done > > >>ReplayGain: -0.8dB > > >>----------------- > > >>As you can see on the line starting with "average" this particular >sample > > >>used joint-stereo on 64% of the frames. > > >> > > >>If you don't have lame installed or can't find a track that produces >both > > >>kind of frames, I can easily put this file somewhere. > > > > > >LR: 849 (35.64%) MS: 1533 (64.36%) > > > > > >Means that 64.36% of the Joint Stereo frames utilise the "+MS" thing ...I > > >have no idea what it is, but I do know it is a Joint Stereo enhancement > > >held in the MODE bits of the header - which are only relevant if the > > >CHANNEL bits are set to Joint Stereo. There is also a "+IS" (intentsity > > >stereo) and the combo "+M/S +IS" > > > > > >BC > > > > > > > > >>David > > >> > > >> > > > >> > >When it comes to sample rate, layer and version switching, I think >you're > > >> > >reasonably safe, though it is probably legal. Stereo mode I think >you > > >>will > > >> > >find encoders may switch from frame to frame. > > >> > > > >> > Is anyone in a position to send me an example file please? Or >seond-best, > > >> > name an encoder with a required set of options. > > >> > > > >> > Difficult to test my app without test data - and quite a chore to > > >> > manufacture such a file by hand. (...and that bit of the app is not >yet > > >> > written) > > >> > > > >> > BC > > >> > > > >> > > > > > Received on 2006-01-14 Page template was last modified "Tue Sep 7 00:00:02 2021" The Rockbox Crew -- Privacy Policy |