htaglib
Bindings to TagLib, audio meta-data library
https://github.com/mrkkrp/htaglib
Version on this page: | 1.1.1 |
LTS Haskell 22.39: | 1.2.1@rev:1 |
Stackage Nightly 2024-10-31: | 1.2.1@rev:1 |
Latest on Hackage: | 1.2.1@rev:1 |
htaglib-1.1.1@sha256:a0ccbab0103dd71e7a35666c7508f82f4282435e97b960818e7f7448d5517c09,2264
Module documentation for 1.1.1
HTagLib
This is Haskell bindings to TagLib, library for reading and editing meta-data of several popular audio formats.
It works with the following formats:
- MP3
- FLAC
- MPC
- Speex
- WavPack TrueAudio
- WAV
- AIFF
- MP4
- ASF
This happens in an abstract, uniform way, so you don’t need to handle any low-level details. As a consequence, it’s currently not possible to work with format-specific functionality.
Alternatives
There is at least two Haskell bindings doing “the same” thing:
Both are very low level, without any protection or higher-level abstractions, not really type-safe. I personally don’t want to use them, so I wrote this.
A note for FLAC users
If you want to work with FLAC, there is
a complete Haskell binding to
libFLAC
—reference FLAC implementation. It allows to work with all FLAC
metadata (read and write) and also provides Haskell API to stream encoder
and stream decoder. Please prefer that package if you don’t need to work
with other audio formats.
Quick start
First, since this is bindings to C-interface of the library, you’ll need to install the library itself. If you’re on a Unix-like system, chances are you’ll have it in the official repositories of your distro.
After installation of the library, install htaglib
package using Cabal or
Stack (recommended):
$ stack install htaglib
Reading meta data
Now to the hacking. It’s recommended that you define a record representing meta-data of audio track in your program, like this:
module Main (main) where
import Data.Monoid
import Sound.HTagLib
import System.Environment (getArgs)
data AudioTrack = AudioTrack
{ atTitle :: Title
, atArtist :: Artist
, atAlbum :: Album
, atComment :: Comment
, atGenre :: Genre
, atYear :: Maybe Year
, atTrack :: Maybe TrackNumber }
deriving Show
A couple of notes here. We use unique types for every component of meta
data, so it’s more difficult to use track title in lieu of track artist, for
example. Meta data that is represented by strings also has smart
constructors, they replace zero bytes with spaces, this is necessary to
avoid troubles when your Haskell strings go to the C-level (well, zero-bytes
in strings is rather edge case, but it should be mentioned). Of course,
Title
, Artist
, Album
, Comment
, and Genre
all are instances of
IsString
, so just turn on OverloadedStrings
and you can use normal
string literals to create data of these types.
Year
and TrackNumber
may be not set or missing, in this case you get
Nothing
. This is possible with string-based fields too, but in that case
you just get empty strings. Year
and TrackNumber
have smart constructors
that make sure that the values are positive (i.e. zero is not allowed).
OK, it’s time to read some info. There is TagGetter
type which is an
applicative functor. You first construct TagGetter
which will retrieve
entire AudioTrack
for you using applicative style:
audioTrackGetter :: TagGetter AudioTrack
audioTrackGetter = AudioTrack
<$> titleGetter
<*> artistGetter
<*> albumGetter
<*> commentGetter
<*> genreGetter
<*> yearGetter
<*> trackNumberGetter
Perfect, now use getTags
to read entire record:
main :: IO ()
main = do
path <- head <$> getArgs
track <- getTags path audioTrackGetter
print track
For example (alignment is added):
$ ./example "/home/mark/music/David Bowie/1977, Low/01 Speed of Life.flac"
AudioTrack
{ atTitle = Title "Speed of Life"
, atArtist = Artist "David Bowie"
, atAlbum = Album "Low"
, atComment = Comment ""
, atGenre = Genre ""
, atYear = Just (Year 1977)
, atTrack = Just (TrackNumber 1)
}
Success! It’s also possible to extract audio properties like sample rate, etc. but it’s not shown here for simplicity, consult Haddocks for more information.
N.B. If you need to extract duration of tracks, TagLib only returns number
of seconds as an integer. This means that if you want to calculate total
duration, you’ll have slightly incorrect result. Proper solution is to
extract duration as floating-point number, for that we recommend bindings to
libsndfile
—hsndfile
(or
the above-mentioned flac
package for Haskell if you work with FLAC).
Writing meta data
We cannot use applicative interface to set tags. There are several reasons:
-
Applicative interface in general is better for extracting or parsing (or rather assembling complex parsers from more basic ones).
-
Some fields like sample rate or length can only be read, not set.
-
We may wish to set one or two fields selectively, not everything.
Solution: use monoids. TagSetter
is an instance of Monoid
. This means
that we can set title and artist of audio track like this:
main :: IO ()
main = do
(path : title : artist : _) <- getArgs
setTags path Nothing $
titleSetter (mkTitle title) <>
artistSetter (mkArtist artist)
track <- getTags path audioTrackGetter
print track
This code loads file and changes “title” and “artist” meta data fields.
Conclusion
With the interface provided by getTags
and setTags
it’s not possible to
forget to close file or free some resource. You can read all meta data at
once directly into your data structure in type-safe manner. Writing meta
data should be trivial too. Have fun!
License
Copyright © 2015–2017 Mark Karpov
Distributed under BSD 3 clause license.
Changes
HTagLib 1.1.1
- Improved/updated documentation and metadata.
HTagLib 1.1.0
- Made
getTags
,getTags'
,setTags
, andsetTags'
callable from any instance ofMonadIO
, not onlyIO
.
HTagLib 1.0.4
-
Re-wrote the test suite with Hspec.
-
Drop support for GHC 7.6.
HTagLib 1.0.3
- Export functions instead of record selectors for tag newtype wrappers. This is to prevent changes (using record syntax) to values created with smart constructors.
HTagLib 1.0.2
- Modify test suite so it passes with newer versions of TagLib as well.
HTagLib 1.0.1
- Rewritten setters (without changing the API), so at most one writing
operation is performed for every settable value. When combining setters
that happen to set the same tags to different values, value on the left
side of
mappend
wins.
HTagLib 1.0.0
-
Make the module
Sound.HTagLib.Internal
hidden for end users. -
Make
Text
underlying type for wrappers around textual data (breaking change, previously it wasString
). -
Rename functions like
getTitle
tounTitle
(breaking change). -
Fix bug when wrong data is read from files when current locale specifies encoding other than UTF-8.
HTagLib 0.1.1
- Missing audio samples used for testing are included in distribution.
HTagLib 0.1.0
- Initial release.