file_data
Ruby library that reads file metadata.
The api provides a basic usage and an advanced usage. The basic usage will reopen and reparse the file every time it is called which is no problem when reading a single value but can be a performance drain for multiple values. The advanced usage allows the user to grab more than one value without having to read the file more than once.
Basic Usage
filepath = '...' # Path to a jpeg or mpeg4 file
# Get the date when the file content originated. When a photo was taken, when a movie was recorded, etc
FileData::FileInfo.origin_date(filepath)
# Get the date when the file was considered to be created. This is usually tied in some way to when the file itself was created on a disk somewhere (not usually as useful as origin date)
FileData::FileInfo.creation_date(filepath)
Advanced Usage
Varies by file format type. Currently there are low level classes for parsing exif and mpeg4 metadata
Exif documentation
Exif data is hierarchical and consists of tag/value pairs. The first level is whether or not the tag applies to the image or the image's thumbnail. Next a tag may be one of several sections and within the section it will have a unique numeric value. So given this terminology a unique key for an exif tag would be something like image/section1/123 for a tag that applies to the image in section 1 with a tag id of 123.
To read exif data a stream of the jpeg data should be used as input. For performance reasons all of the data that is desired should be extracted in a single method from FileData::Exif. All methods will manipulate the stream position after they are called and the user should not count on the stream position being at a specific location after a FileData::Exif method call.
Examples:
## Get Exif data from a file path or stream
# The file path or stream is passed as a parameter to class methods on FileData::Exif
# rather than having the file path or stream set in the constructor and the methods
# be instance methods to ensure that the user falls into a "pit of success" by only
# opening the file once to get tag values rather than potentially multiple times
# Get image exif data from a file path...
hash = FileData::Exif.image_data_only('/path/to/file.jpg')
# Get thumbnail exif data from a file stream...
File.open('/path/to/file.jpg', 'rb') do |f|
hash = FileData::Exif.thumbnail_data_only(f)
end
## Extract values depending on how much data is returned
# Image and thumbnail data are returned as a hash with keys
# being the full tag name if it exists in FileData::ExifTags (see below listing)
# or "#{ifd_id}-#{tag_id}" if there is no existing name for the tag in FileData::ExifTags
image_hash = FileData::Exif.image_data_only(file_path_or_stream)
image_description_value = image_hash[:Other_ImageDescription]
unknown_gps_tag_value = image_hash["34853-99999"]
thumbnail_hash = FileData::Exif.thumbnail_data_only(file_path_or_stream)
image_width_tag_value = thumbnail_hash[:Image_Structure_Width]
unknown_gps_tag_value = thumbnail_hash["Tiff-99999"]
all_data = FileData::Exif.all_data(file_path_or_stream)
image_hash = all_data.image
thumbnail_hash = all_data.thumbnail
# For extracting only a specific tag the value is returned and the search key must be
# an array matching the keys needed to get traverse FileData:ExifTags (see below listing)
image_description_value = FileData::Exif.only_image_tag(file_path_or_stream, [:Tiff, 270])
unknown_exif_tag_value = FileData::Exif.only_thumbnail_tag(file_path_or_stream, [34665, 2])
Known Tag Keys
Below is the contents of FileData::ExifTags.tag_groups which lists all known tag keys and their uniquely assigned names
# Tiff Tags (0th and 1st IFDs)
FileData::ExifTags.tag_groups[:Tiff] =
{
256 => :Image_Structure_Width,
257 => :Image_Structure_Length,
258 => :Image_Structure_BitsPerSample,
259 => :Image_Structure_Compression,
262 => :Image_Structure_PhotometricInterpretation,
270 => :Other_ImageDescription,
271 => :Other_Make,
272 => :Other_Model,
273 => :Recording_StripOffsets,
274 => :Image_Structure_Orientation,
277 => :Image_Structure_SamplesPerPixel,
278 => :Recording_RowsPerStrip,
279 => :Recording_StripByteCounts,
283 => :Image_Structure_YResolution,
284 => :Image_Structure_PlanarConfiguration,
296 => :Image_Structure_ResolutionUnit,
301 => :Image_Data_TransferFunction,
305 => :Other_Software,
306 => :Other_DateTime,
315 => :Other_Artist,
318 => :Image_Data_WhitePoint,
319 => :Image_Data_PrimaryChromaticities,
513 => :Recording_JPEGInterchangeFormat,
514 => :Recording_JPEGInterchangeFormatLength,
529 => :Image_Data_YCbCrCoefficients,
530 => :Image_Structure_YCbCrSubSampling,
531 => :Image_Structure_YCbCrPositioning,
532 => :Image_Data_ReferenceBlackWhite,
33_432 => :Other_Copyright
}
# Exif IFD Tags
FileData::ExifTags.tag_groups[34_665] =
{
33_434 => :Exif_PictureTakingConditions_ExposureTime,
33_437 => :Exif_PictureTakingConditions_FNumber,
34_850 => :Exif_PictureTakingConditions_ExposureProgram,
34_852 => :Exif_PictureTakingConditions_SpectralSensitivity,
34_855 => :Exif_PictureTakingConditions_PhotographicSensitivity,
34_856 => :Exif_PictureTakingConditions_OECF,
34_864 => :Exif_PictureTakingConditions_SensitivityType,
34_865 => :Exif_PictureTakingConditions_StandardOutputSensitivity,
34_866 => :Exif_PictureTakingConditions_RecommendedExposureIndex,
34_867 => :Exif_PictureTakingConditions_ISOSpeed,
34_868 => :Exif_PictureTakingConditions_ISOSpeedLatitudeyyy,
34_869 => :Exif_PictureTakingConditions_ISOSpeedLatitudezzz,
36_864 => :Exif_Version_ExifVersion,
36_867 => :Exif_DateAndTime_DateTimeOriginal,
36_868 => :Exif_DateAndTime_DateTimeDigitized,
37_121 => :Exif_Configuration_ComponentsConfiguration,
37_122 => :Exif_Configuration_CompressedBitsPerPixel,
37_377 => :Exif_PictureTakingConditions_ShutterSpeedValue,
37_378 => :Exif_PictureTakingConditions_ApertureValue,
37_379 => :Exif_PictureTakingConditions_BrightnessValue,
37_380 => :Exif_PictureTakingConditions_ExposureBiasValue,
37_381 => :Exif_PictureTakingConditions_MaxApertureValue,
37_382 => :Exif_PictureTakingConditions_SubjectDistance,
37_383 => :Exif_PictureTakingConditions_MeteringMode,
37_384 => :Exif_PictureTakingConditions_LightSource,
37_385 => :Exif_PictureTakingConditions_Flash,
37_396 => :Exif_PictureTakingConditions_SubjectArea,
37_386 => :Exif_PictureTakingConditions_FocalLength,
37_500 => :Exif_Configuration_MakerNote,
37_510 => :Exif_Configuration_UserComment,
37_520 => :Exif_DateAndTime_SubsecTime,
37_521 => :Exif_DateAndTime_SubsecTimeOriginal,
37_522 => :Exif_DateAndTime_SubsecTimeDigitized,
37_888 => :Exif_ShootingSituation_Temperature,
37_889 => :Exif_ShootingSituation_Humidity,
37_890 => :Exif_ShootingSituation_Pressure,
37_891 => :Exif_ShootingSituation_WaterDepth,
37_892 => :Exif_ShootingSituation_Acceleration,
37_893 => :Exif_ShootingSituation_CameraElevationAngle,
40_960 => :Exif_Version_FlashpixVersion,
40_961 => :Exif_ColorSpace_ColorSpace,
40_962 => :Exif_Configuration_PixelXDimension,
40_963 => :Exif_Configuration_PixelYDimension,
40_964 => :Exif_RelatedFile_RelatedSoundFile,
41_483 => :Exif_PictureTakingConditions_FlashEnergy,
41_484 => :Exif_PictureTakingConditions_SpatialFrequencyResponse,
41_486 => :Exif_PictureTakingConditions_FocalPlaneXResolution,
41_487 => :Exif_PictureTakingConditions_FocalPlaneYResolution,
41_488 => :Exif_PictureTakingConditions_FocalPlanResolutionUnit,
41_492 => :Exif_PictureTakingConditions_SubjectLocation,
41_493 => :Exif_PictureTakingConditions_ExposureIndex,
41_495 => :Exif_PictureTakingConditions_SensingMode,
41_728 => :Exif_PictureTakingConditions_FileSource,
41_729 => :Exif_PictureTakingConditions_SceneType,
41_730 => :Exif_PictureTakingConditions_CFAPattern,
41_985 => :Exif_PictureTakingConditions_CustomRendered,
41_986 => :Exif_PictureTakingConditions_ExposureMode,
41_987 => :Exif_PictureTakingConditions_WhiteBalance,
41_988 => :Exif_PictureTakingConditions_DigitalZoomRatio,
41_989 => :Exif_PictureTakingConditions_FocalLengthIn35mmFilm,
41_990 => :Exif_PictureTakingConditions_SceneCaptureType,
41_991 => :Exif_PictureTakingConditions_GainControl,
41_992 => :Exif_PictureTakingConditions_Contrast,
41_993 => :Exif_PictureTakingConditions_Saturation,
41_994 => :Exif_PictureTakingConditions_Sharpness,
41_995 => :Exif_PictureTakingConditions_DeviceSettingDescription,
41_996 => :Exif_PictureTakingConditions_SubjectDistanceRange,
42_016 => :Exif_Other_ImageUniqueID,
42_032 => :Exif_Other_CameraOwnerName,
42_033 => :Exif_Other_BodySerialNumber,
42_034 => :Exif_Other_LensSpecification,
42_035 => :Exif_Other_LensMake,
42_036 => :Exif_Other_LensModel,
42_037 => :Exif_Other_LensSerialNumber,
42_240 => :Exif_ColorSpace_Gamma
}
# GPS IFD Tags
FileData::ExifTags.tag_groups[34_853] =
{
0 => :GPS_Version,
1 => :GPS_LatitudeRef,
2 => :GPS_Latitude,
3 => :GPS_LongitudeRef,
4 => :GPS_Longitude,
5 => :GPS_AltitudeRef,
6 => :GPS_Altitude,
7 => :GPS_TimeStamp,
8 => :GPS_Satellites,
9 => :GPS_Status,
10 => :GPS_MeasureMode,
11 => :GPS_DOP,
12 => :GPS_SpeedRef,
13 => :GPS_Speed,
14 => :GPS_TrackRef,
15 => :GPS_Track,
16 => :GPS_ImgDirectionRef,
17 => :GPS_ImgDirection,
18 => :GPS_MapDatum,
19 => :GPS_DestLatitudeRef,
20 => :GPS_DestLatitude,
21 => :GPS_DestLongitudeRef,
22 => :GPS_DestLongitude,
23 => :GPS_DestBearingRef,
24 => :GPS_DestBearing,
25 => :GPS_DestDistanceRef,
26 => :GPS_DestDistance,
27 => :GPS_ProcessingMethod,
28 => :GPS_AreaInformation,
29 => :GPS_DateStamp,
30 => :GPS_Differential,
31 => :GPS_HPositioningError
}
# Interoperability IFD Tags
FileData::ExifTags.tag_groups[40_965] =
{
1 => :Interoperability_Index
}
Mpeg4 documentation
filepath = '...' # path to an mpeg4 file
File.open(filepath, 'rb') do |stream|
parser = FileData::MvhdBoxParser # class that parses the box you want
method = :creation_time # attribute to get from the parse result
box_path = ['moov', 'mvhd'] # path to get to the box that you want
# final result that you are looking for
result = FileData::Mpeg4.get_value(stream, parser, method, *box_path)
end