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Posted by reply on 12/17/06 22:47
On Sun, 17 Dec 2006 16:16:45 -0500, "JJ" <up@yours.spammers> wrote:
|I'm trying to convert the bit rate on some MP3 files from 160/192 to 128
|using LAME 3.97. (Why down? Well, because the lower bit rate is required by
|the hardware I'm using the files on; more in a moment.)
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|The issue I'm experiencing is that no matter what software I use, I get a
|tiny amount of extra space (silence) at the beginning of the converted file.
|For example, when using the Windows Audio Converter (part of the Windows
|Digital Media Enhancements package) I get .037 seconds of blank space. When
|using LAME under GoldWave, Audacity, or winLAME, I get either .051 or .025
|seconds of space (.025 if I select NoGap in winLAME).
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|Now you may be thinking "That's an imperceptible amount of silence" and I'd
|agree with you if this were for listening purposes, but these files are for
|use with a dance game (kind of like DDR) and this gap has an absolutely
|obvious effect on step timing. Is there anything I can do to get the
|converted file to begin at exactly the same point in time? At first I simply
|tried deleting that time from the beginning of the file and re-exporting
|from Audacity but the time reappears!
|
Are you sure this silence is in the file itself and not a gap in playback
through your player when going from one mp3 to another? Here's a quote from
the Design Limitations listed on http://en.wikipedia.org/wiki/MP3
"Encoder/decoder overall delay is not defined, which means lack of official
provision for gapless playback. However, some encoders such as LAME can attach
additional metadata that will allow players that are aware of it to deliver
gapless playback."
The player must read the first frame in full before it can play it, so unless
the player is reading ahead, there will always be a one frame length gap in
the playback. A rough check on a sample encoded at 128 kbs, 44.1 khz, stereo
showed a frame length of about .026 seconds (fixed bit rate was used). That
would tell me that any player I used would require 0.026 seconds before it
could start spitting out any sound.
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