100 lines
5.0 KiB
Markdown
100 lines
5.0 KiB
Markdown
# Tag Parser
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C++ library for reading and writing MP4 (iTunes), ID3, Vorbis, Opus, FLAC and Matroska tags.
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## Supported formats
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The tag library can read and write the following tag formats:
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* iTunes-style MP4/M4A tags (MP4-DASH is supported)
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* ID3v1 and ID3v2 tags
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* conversion between ID3v1 and different versions of ID3v2 is possible
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* mainly for use in MP3 files but can be added to any kind of file
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* Vorbis, Opus and FLAC comments in Ogg streams
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* cover art via "METADATA_BLOCK_PICTURE" is supported
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* Vorbis comments and "METADATA_BLOCK_PICTURE" in raw FLAC streams
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* Matroska/WebM tags and attachments
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Further remarks:
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* Unsupported file contents (such as unsupported tag formats) are *generally* preserved as-is.
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* Note that APE tags are *not* supported. APE tags in the beginning of a file are strongly
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unrecommended and thus discarded when applying changes. APE tags at the end of the file
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are preserved as-is when applying changes.
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## File layout options
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### Tag position
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The library allows you to choose whether tags should be placed at the beginning or at
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the end of an MP4/Matroska file.
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### Padding
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Padding allows adding additional tag information without rewriting the entire file
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or appending the tag. Usage of padding can be configured:
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* minimum/maximum padding: The file is rewritten if the padding would fall below/exceed the specified limits.
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* preferred padding: If the file needs to be rewritten the preferred padding is used.
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Default value for minimum and maximum padding is zero. Hence the library will almost always have to rewrite
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the entire file to apply changes. To prevent this, set at least the maximum padding to a higher value.
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It is also possible to force rewriting the entire file always.
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Taking advantage of padding is currently not supported when dealing with Ogg streams (it is supported when dealing with raw FLAC streams).
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## Additional features
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The library can also display technical information such as the ID, format, language, bitrate,
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duration, size, timestamps, sampling frequency, FPS and other information of the tracks.
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It also allows to inspect and validate the element structure of MP4 and Matroska files.
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## Text encoding, Unicode support
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The library is aware of different text encodings and can convert between different encodings using iconv.
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## Usage
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* For building/installing the library, checkout the build instructions below.
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* To use the library with CMake, use its find module (e.g. `find_package(tagparser 10.1.0 REQUIRED)`) which
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provides the imported target `tagparser` you can link against. Otherwise, use the `pkg-config` module
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`tagparser` to query the required compiler/linker flags.
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* For a code example that shows how to read and write tag fields in a format-independent way, have
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a look at [`example.cpp`](doc/example.cpp).
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* The most important class is `TagParser::MediaFileInfo` providing access to everything else.
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* IO errors are propagated via standard `std::ios_base::failure`.
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* Fatal processing errors are propagated by throwing a class derived from `TagParser::Failure`.
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* All operations which might generate warnings, non-fatal errors, ... take a `TagParser::Diagnostics` object to store
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those messages.
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* All operations which might be aborted or might provide progress feedback take a `TagParser::AbortableProgressFeedback`
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object for callbacks and aborting.
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* Field values are stored using `TagParser::TagValue` objects. Those objects erase the actual type similar to `QVariant`
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from the Qt framework. The documentation of `TagParser::TagValue` covers how different types and encodings are
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handled.
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### Further documentation
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For more examples check out the command line interface of [Tag Editor](https://github.com/Martchus/tageditor).
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API documentation can be generated using Doxygen with `cmake --build … --target tagparser_apidoc`.
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## Bugs, stability
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Bugs can be reported on GitHub.
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It is recommend to create backups before editing because I can not test whether the library
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works with all kinds of files. (When forcing rewrite a backup is always created.)
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## Build instructions
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The tagparser library depends on [c++utilities](https://github.com/Martchus/cpp-utilities) and is built
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in the same way.
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It also depends on zlib, [iso-codes](https://salsa.debian.org/iso-codes-team/iso-codes) and requires at
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least CMake 3.19. Tests depend on CppUnit. For checking integrity of testfiles, the OpenSSL crypto library is
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required.
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The location of the JSON file from iso-codes can be specified via the CMake variable `LANGUAGE_FILE_ISO_639_2`.
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For building multiple projects in one go (c++utilities, tagparser and the tag editor), checkout
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the ["Building this straight"](https://github.com/Martchus/tageditor#building-this-straight) instructions.
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## TODOs
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* Support more formats (EXIF, PDF metadata, Theora, ...)
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* Support adding cue-sheet to FLAC files
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More TODOs are tracked in the [issue section at GitHub](https://github.com/Martchus/tagparser/issues).
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## Copyright notice and license
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Copyright © 2015-2024 Marius Kittler
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All code is licensed under [GPL-2-or-later](LICENSE).
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