Forgot to ask... how is it that you are getting the length of these
audio files?
Erick
On Mar 31, 2006, at 4:51 PM, Jeffrey Mattox wrote:
Summary:
The RB MoviePlayer appears to be using a sample rate of 43,892 kHz
for mp3 files, instead of 44,100 kHz.
Details:
I am processing 53-minute mp3 files (podcasts) and, among other
things, visualizing the waveform. To get the audio samples, I am
using Dave Addey's code posted on the RB forums and here:
http://tinyurl.com/pzlnt
I discovered a problem when trying to match the player position
with the corresponding audio sample in the waveform.
Observations:
If I use Sound Studio to convert the file to AIFF, then everything
is fine, and I get consistent readings from these various sources:
iTunes, Finder, QuickTime Player, Sound Studio, and my RB
application:
Length: 53:00 (mm:ss)
Sample rate: 44,100 kHz
Samples: 140,234,105
Mysteries:
1. If I use the original mp3 file, then the RB MoviePlayer reports
the length as 53:15 (and it actually takes that long to play). QT
Player and iTunes still report 53:00 when using the mp3.
2. The code referenced above thinks the sample rate is 44,100, but
it generates 140,899,941 samples (at 44,100 that is 53:15) of which
the last 665,836 samples are zero (a "tail"). Prior to the tail,
there are 140,234,105 useful samples (same as the AIFF). Somehow,
this code thinks the length is 53:15, too, even though it still
uses 44,100 kHz for the valid samples.
So, it appears that the RB player is using a sample rate of 43,892
kHz. That accounts for the extra 15 seconds. I can correlate the
RB position to the samples as follows:
sample_index = MyMoviePlayer.Position * 43892
Can you offer any insights into these mysteries? And is there a
way to fetch the sample rate being used by the MoviePlayer?
Jeff
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