Re: [Audacity-devel] mp3 export P2
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From: Gale A. <ga...@au...> - 2008-12-28 17:56:07
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| From "Michael Chinen" <mc...@gm...> | Wed, 24 Dec 2008 16:37:13 -0500 | Subject: [Audacity-devel] mp3 export P2 > P2 MP3 Export: (normal and export multiple): Bit Rate > Mode and Quality choices in Options dialogue are non-functional, > almost always producing a 128 kbps CBR file. Additionally, > the reported length is often incorrect although the actual length > is correct. > > [MC] Looking into as of 16 Dec 08. Initial investigation (on Mac) > shows that only VBR files have the wrong time info, and that all > of the options are used for the export (all the file lengths are different > and show different bitrates according to quicktime and iTunes.) > No solutions yet, but as quicktime and other software plays it correctly, > and itunes doesn't, it appears that the wrong duration is a bug in itunes, > which ignores the vbr header in the mp3 encoding. > Update (24 Dec 08) tried exporting with a number of flag/checksum options > that were rumored to be a possible fix, but nothing seems to work as far as > VBR and iTunes. > > It looks like half of this bug is fixed - CBR and ABR seem to work fine. > I've found forums claiming that there is no way to get lame to work with > itunes when using VBR besides using another tool to edit the header. > I'm no expert on VBR or mp3, but it looks like there are several types of > VBR headers and iTunes doesn't read the one that is made by lame, so for > VBR it estimates the duration by the first bitrate. Strangely enough, > quicktime does just fine. > > Any ideas how to proceed? is this still a bug given that it works in quicktime? Many apps. seem to have problems with the reported length of our VBR MP3s on Windows too (Winamp, Foobar, iTunes), but Explorer and QuickTime see it right. I hope Leland has a fix for reported length, but on Windows using lame_enc.dll 3.98.2, VBR remains broken (files same bit rate and size), just as with past versions of lame_enc.dll (as confirmed by David Bailes). * I exported a mono track with all ten variable bit rate settings and all ten produced Constant Bit Rate (as reported by dBPowerAmp) 128 kbps files. They are all the same size. * I repeated all ten variable bit rate settings with a stereo track and all but one produced a CBR 128 kbps file. The other one was correct. * All the presets (except of course Insane) produce likewise a CBR 128 kbps file. * ABR does seem OK here, and according to Winamp the Stereo/ Joint Stereo export option seems to be working as well. I note there is no issue exporting with LAME v3.98.2 via (external program) - VBR files are always the requested bit rate, and reported length correct. The bug can't be cleared until VBR works properly with lame_enc.dll on Windows. Gale |