Edit ID3 tag interactively (uses curses/ncurses functions)
Delete ID3 tag (if one exists)
Force Mode: Treat all files as MP3s even if MP3 frames can't be found
Do a Full scan for technical information (see the section Speed Considerations below for more information)
Print MP3 attributes according to FORMAT_STRING. FORMAT_STRING is
similar to a printf(3) format string in that it is printed verbatim except
for the following conversions and escape sequences. Any conversion specifier may
optionally include the various alignment, precision, and field width modifiers
accepted by printf(3). See
the EXAMPLES section below for examples of how format strings are used
Filename without the path [string]
Filename with the path [string]
File size in KB [integer]
Musical genre [string]
Musical genre number [integer]
Album name [string]
Track Title [string]
Copyright flag [string]
CRC Error protection [string]
MPEG Layer [string]
Original material flag [string]
Stereo/mono mode [string]
MPEG Version [float]
Number of good audio frames [integer]
Number of corrupt audio frames [integer]
Sampling frequency in Hz [integer]
Sampling frequency in KHz [integer]
Bit Rate in KB/s (type and meaning affected by -r option)
Playing time: minutes only [integer]
Playing time: seconds only [integer] (usually used in conjunction with %m)
Total playing time in seconds [integer]
A single percent sign
Audible Alert (terminal bell)
Any arbitrary character specified by the hexidecimal number hh
Any arbitrary character specified by the octal number ooo
A single backslash character
Specifying MP3 files without any other options displays the existing ID3 tag (if any).
Specifying a track number of 0 reverts an ID3 tag to 1.0 format
Non-specified ID3 fields, if existant, will remain unchanged.
Genres can be specified as numbers or names: -g 17 same as -g Rock
Multiple word fields must be enclosed in quotes (eg: -t "A title")
- Speed Considerations
In order to determine certain technical attributes (playing time, number of
frames, number of bad frames, and in a few cases the bit rate) with absolute
certainty, it would be necessary to read the entire MP3 file. Mp3info normally
tries to speed things up by reading a handful of frames from various points in
the file and estimating the statistics for the rest of the file based on those
samples. Usually, this results in very accurate estimates. Audio playing times
are usually off by no more than a second, and the number of frames is off by
less than 0.1%. Often the estimates agree exactly with the full scans.
Nevertheless, the user may wish to ensure that she is getting exact information.
One should specify the -F switch if one wants mp3info to read the entire
MP3 file when determining this information. Note that a full scan will only
affect mp3info's output if the -x switch is used or the -p switch is
used with a FORMAT_SPECIFIER containing %m, %s, %S, %u
or (rarely) %r. Using the -F switch under other conditions will
only slow down mp3info. Also note that a FORMAT_SPECIFIER containing %b
or a VBR MP3 file will automatically trigger a full scan even if the -F
switch is not used.
Several users have noted that the %u specifier used alone:
mp3info -p "%u" song.mp3
sometimes gives a different number of good frames than when used with the %b specifier:
mp3info -p "%u %b" song.mp3
This is because when you use %u by itself, mp3info only estimates the
number of frames based on the bitrate and the size of the file. When you use
the %b specifier, you force mp3info to do a full scan of the file which
guarantees an accurate count of both the good and bad frames. If you want to
guarantee an accurate count of the number of good frames when using %u
by itself, you should use the -F option.
- Bit Rates
MP3 files are made up of many (usally several thousand) audio blocks called 'frames'.
Each of these frames is encoded at a specific 'bit rate' which
determines both the quality of the sound and the size of the frame itself. Bit
rates can range from 8 Kb/s (kilobits per second) to 320 Kb/s. Note that the
MP3 specification only allows 14 discreet bit rates for an MP3 file, so, for
instance, a stereo MP3 could have frames with bit rates of 128 Kb/s and 160
Kb/s, but nowhere in between.
Audio frames with high bit rates sound much better than those with lower bit
rates, but take up more space. Obviously, one would like to use a bit rate that
is only high enough to maintain a comfortable level of audio quality. Normally,
all the frames in an MP3 file are encoded at the same bit rate. A few MP3
files, however, are encoded such that the bit rate may vary from one frame to
the next. These MP3 files are called Variable Bit Rate (or VBR) files. Since
VBR files do not have one single bit rate, attempting to report the bit rate of
the file as a whole can be problematic. Consequently,
mp3info allows you to specify how you want this value reported.
The default is to simply print the word 'Variable' where the bit rate would
normally appear. Another option is to print the mathematical average of all
the frames. This has the advantage of being completely accurate, but the number
printed may not correspond to one of the 14 discreet bit rates that would be
allowed for that file. The third alternative solves that problem by allowing
the bit rate to be reported as the median bit rate which is what you would get
if you lined up all the frames in the file by bit rate from lowest to highest
and picked the
frame closest to the middle of the line.
For more specific usage information, see the -r switch and the %r
conversion specifier under the description of
Display existing ID3 tag information (if any) in song.mp3
Set the title, author and genre of song.mp3. (All other fields unchanged)
mp3info -t "Song Title" -a Author -g "Rock & Roll" song.mp3
Set the album field of all MP3 files in the current directory
to "The White Album"
mp3info -l "The White Album" *.mp3
Delete the entire ID3 tag from song1.mp3 and song2.mp3
mp3info -d song1.mp3 song2.mp3
Delete the comment field from the ID3 tags of all MP3 files
in the current directory. (All other fields unchanged)
mp3info -c "" *.mp3
Display the Title, Artist, Album, and Year of all MP3 files in the current directory.
We include the labels 'File', etc. and insert newlines (\n) to make things
more readable for humans:
mp3info -p "File: %f\nTitle: %t\nArtist: %a\nAlbum: %l\nYear: %y\n\n" *.mp3
Say you want to build a spreadsheet of your MP3 files. Here's a command you might use
to help you accomplish that. Most spreadsheet programs will import an ASCII file and treat
a given character as a field separator. A commonly used field separator is the tab character.
For each MP3 file in the current directory, we want to output the filename, title, artist,
and album on a single line and have the fields separated by a tab (\t) character. Note
that you must include a newline (\n) at the end of the format string in order
to get each file's information on a separate line. Here's the command:
mp3info -p "%f\t%t\t%a\t%l\t%y\n" *.mp3
Some spreadsheets or other software may allow importing data from flat files
where each field is a specific width. Here's where the format modifers come into
play. This next command outputs the same information as the command above, but uses
fixed-width fields instead of tab separators. The filename field is defined as
50 characters wide, the title field is defined as 31 characters wide, and so on.
mp3info -p "%50f%31t%31a%31l%4y\n" *.mp3
The problem with the output of this command is that all strings are normally right-
justified within their fields. This looks a little odd since most western
languages read from left to right. In order to make
the fields left-justified, add a minus sign (-) in front of the field-width:
mp3info -p "%-50f%-31t%-31a%-31l%-4y\n" *.mp3
Now suppose you just want the running time of each MP3 file specified in minutes
and seconds. Simple enough:
mp3info -p "%f: %m:%s\n" *.mp3
You may notice when you do this, however, that leading zeros are not displayed
in the seconds field (%s). So for instance, if you had a
track four minutes and two seconds long its running time would be displayed
as '4:2' instead of '4:02'. In order to tell mp3info to pad an integer field
with zeros, you need to use a field width modifier and place a zero in front of it.
The following command is the same as the previous one, but it specifies that mp3info
is to display the seconds field with a fixed
field-width of two characters and to pad the field with leading zeros if necessary:
mp3info -p "%f: %m:%02s\n" *.mp3
The last trick we have to show you is the precision specifier for floating point
variables. The following command displays the filename and average bit rate for
all MP3 files in the current directory.
mp3info -r a -p "%f %r\n" *.mp3
By default, the floating point value of the average bit rate is displayed with six
digits past the decimal point (ex: 175.654332). If you are like me, this seems like a bit
of overkill. At most you want one or two digits beyond the decimal place displayed. Or you
might not want any. The following command displays the average bit rate with first two, then
zero digits beyond the decimal point:
mp3info -r a -p "%f %.2r %.0r\n" *.mp3
If you wanted to specify a field width for a floating point value, you could do that by
placing the field-width before the decimal point in the field modifier. This command does
just that -- specifying an average bit-rate field six characters wide that will show two
digits of precision beyond the decimal point:
mp3info -r a -p "%f %6.2r\n" *.mp3
There's no "save and quit" in interactive mode. You must fill in all the
fields (even if it is with blanks) and let the program finish by itself.
CTRL+C does leave MP3info, but the data isn't saved.
Using space to erase tags in interactive mode does not work correctly if you
then backspace over the deleted text.
The title, author, album, and comment fields are limited to 30 characters.
This is a limitation of the ID3 1.0 tag format, not MP3Info. If you specify
the track number (with the -n switch), the ID3 1.0 tag becomes a 1.1 tag and the
comment field is limited to 28 characters. This is because the difference
between ID3 1.0 and 1.1 is that the tag number is stored in the last byte of
the comment field. This trick "borrows" two bytes from the fixed-length
comment field effectively reducing the maximum comment by two characters.
Genres cannot be specified arbitrarily. They must be specified from a
pre-determined list (use mp3info -G to see that list). Again, this is a
limitation of the ID3 1.0 tag format.
Only ID3 versions 1.0 and 1.1 are supported. ID3V2 is a much more powerful
standard and is planned for some as-yet-undetermined future version. Unfortunately,
a clean implementation is a heck of a lot of work and I'm unbelievably lazy, so don't
hold your breath. It is probably worth noting at this juncture, however, that I do
accept patches. :-)
Exit codes are somewhat haphazard and not well documented.
Cedric Tefft <firstname.lastname@example.org>
- SEE ALSO
This document was created by man2html on November 6, 2006.