Re: Length Mismatch in transcoded file(.wav) and source file (.mp3)
Re: Length Mismatch in transcoded file(.wav) and source file (.mp3)
- Subject: Re: Length Mismatch in transcoded file(.wav) and source file (.mp3)
- From: "Stephen F. Booth" <email@hidden>
- Date: Sat, 12 Jun 2010 07:51:45 -0700
I'm not 100% sure this is the problem you're seeing, but I've had similar issues in the past. Do you know which MP3 encoder was used to create the MP3 in question?
Many MP3s contain an empty MPEG frame at the beginning- the Xing header which contains information on the number of samples, the number of bytes, and seek points. LAME encoded MP3s contain additional data as well (encoder delay and padding, essentially the MDCT filterbank delay, which is useful for gapless playback).
Last time I checked (on 10.5 IIRC) the Core Audio MP3 decoder did not handle the Xing/LAME header, so you will never be able to get gapless playback from MP3s using their decoder unless you manually determine if a Xing or LAME header is present and discard an appropriate number of samples.
The symptom of this is extra silence at the beginning of the decoded audio, which is the Xing header plus the filterbank delay.
Stephen
On Sat, Jun 12, 2010 at 7:23 AM, Abhinav Tyagi
<apple.lists.id@gmail.com> wrote:
Hi all,
I was doing audio transcoding using AudioConverterFillcomplexBuffer in
which I found that the length of the transcoded wave file is different
than the source mp3 file.
I amalso providing the screenshots which is taken by using Quicktime
Inspector for these files.
Can anybody tell this. Although the length is approximately same but
can make significant difference if data is received from stream,
transcoded and restreamed from the transcoded data.
Also there are lots of zero bytes in the begining of the data chunk in
the transcoded RIFF-WAVE. I also reported this earlier but no concrete
response on this.
Any guesses???
SCREENSHOTS of mp3 and wavefile for properties shown by quicktime:
mp3->
http://ScrnSht.com/pxebfc
wave->
http://ScrnSht.com/dcglzp
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