Database Exports

Unless otherwise stated, all multibyte numbers in the file are stored in little-endian byte order. Field names used in the byte field diagrams match the IDs assigned to them in the Kaitai Struct specification,^[1] unless that is too long to fit, in which case a subscripted abbreviation is used, and the text will mention the actual struct field name.

The first page begins with the file header, shown below. The header starts with four zero bytes, followed by a four-byte integer, len_page at byte 04, that establishes the size of each page (including this first one), in bytes. This is followed by another four-byte integer, num_tables at byte 08, which reports the number of different tables that are present in the file. Each table will have a table pointer entry in the “Table pointers” section of the file header, described below, that identifies and locates the table.

The four-byte integer next_u at byte 0c has an unknown purpose, but Mr. Lesniak named it next_unused_page and said “Not used as any empty_candidate, points past the end of the file.” The four-byte integer sequence, at byte 14, was described “Always incremented by at least one, sometimes by two or three.” and I assume this means it reflects a version number that rekordbox updates when synchronizing to the exported media.

Finally, there is another series of four zero bytes, and then the header ends with the list of table pointers which begins at byte 1c. There are as many of these as specified by num_tables, and each has the following structure:

Each Table Pointer is a series of four four-byte integers. The first, type, identifies the type of table being defined. The known table types are shown in below. The second value, at byte 04 of the table pointer, was called empty_candidate by Mr. Lesniak. It may link to a chain of empty pages if the database is ever garbage collected, but this is speculation on my part.

Other than the type, the two important values are first_page at byte 08 and last_page at byte 0c. These tell us how to find the table. They are page indices, where the page containing the file header has index 0, the page with index 1 begins at byte len_page, and so on. In other words, the first page of the table identified by the current table pointer can be found within the file starting at the byte len_page × first_page.

The table is a linked list of pages: each page contains the index of the next page after it. However, you need to keep track of the last_page value for the table, because it tells you not to try to follow the next page link once you reach the page with that index. (If you do keep going, you will start reading pages of some different table.) The structure of the table pages themselves are described in the next section.

As far as we know, the remainder of the first page after the table pointers is unused.

The table header is followed by the table pages themselves. These each have the size specified by len_page in the above diagram, and the following structure:

Data pages all seem to have the header structure described here, but not all of them actually store data. Some of them are “strange” and we have not yet figured out why. The discussion below describes how to recognize a strange page, and avoid trying to read it as a data page.

The first four bytes of a table page always seem to be zero. This is followed by a four-byte value page_index which identifies the index of this page within the list of table pages (the header has index 0, the first actual data page the index 1, and so on). This value seems to be redundant, because it can be calculated by dividing the offset of the start of the page by len_page, but perhaps it serves as a sanity check.

This is followed by another four-byte value, type, which identifies the type of the page, using the values shown in the preceding table. This again seems redundant because the table header which was followed to reach this page also identified the table type, but perhaps it is another sanity check, or an alternate way to tell, when following page links, that you have reached the end of the table you are interested in. Speaking of which, the next four-byte value, next_page, is that link: it identifies the index at which the next page of this table can be found, as long as we have not already reached the final page of the table, as described in File Header.

The exact meaning of unknown₁ is unclear. Mr. Flesinak said “sequence number (0→1: 8→13, 1→2: 22, 2→3: 27)” but I don’t know how to interpret that. Even less is known about unknown₂ . But num_rows_small at byte 18 within the page (abbreviated n_rs in the byte field diagram above) holds the number of rows that are present in the page, unless num_rows_large (below) holds a value that is larger than it (but not equal to 1fff). This seems like a strange mechanism for dealing with the fact that some tables (like playlist entries) have a lot of very small rows, too many to count with a single byte. But then why not just always use num_rows_large?

The purpose of the next two bytes are is also unclear. Of u₃ Mr. Flesniak said “a bitmask (first track: 32)”, and he described u₄ as “often 0, sometimes larger, especially for pages with a high number of rows (e.g. 12 for 101 rows)”.

Byte 1b is called page_flags (abbreviated p_f in the diagram). According to Mr. Flesniak, “strange” (non-data) pages will have the value 44 or 64, and other pages have had the values 24 or 34. Crate Digger considers a page to be a data page if page_flags&40 = `0`.

Bytes 1c-1d are called free_size (abbreviated free_s in the diagram), and store the amount of unused space in the page heap (excluding the row index which is built backwards from the end of the page); used_size at bytes 1c-1d (abbreviated used_s) stores the number of bytes that are in use in the page heap.

Bytes 20-21, u₅ , are of unclear purpose. Mr. Flesniak labeled them “(0→1: 2).”

Bytes 22-23, num_rows_large (abbreviated num_rl in the diagram) hold the number of entries in the row index at the end of the page when that value is too large to fit into num_rows_small (as mentioned above), and that situation seems to be indicated when this value is larger than num_rows_small, but not equal to 1fff.

u₆ at bytes 24-25 seems to have the value 1004 for strange pages, and 0000 for data pages. And Mr. Flesniak describes u₇ at bytes 26-27 as “always 0 except 1 for history pages, num entries for strange pages?”

After these header fields comes the page heap. Rows are allocated within this heap starting at byte 28. Since rows can be different sizes, there needs to be a way to locate them. This takes the form of a row index, which is built from the end of the page backwards, in groups of up to sixteen row pointers along with a bitmask saying which of those rows are still part of the table (they might have been deleted). The number of row index entries is determined, as described above, by the value of either num_rows_small or num_rows_large.

The bit mask for the first group of up to sixteen rows, labeled row_pf0 in the diagram (meaning “row presence flags group 0”), is found near the end of the page. The last two bytes after each row bitmask (for example pad₀ after row_pf0) have an unknown purpose and may always be zero, and the row_pf0 bitmask takes up the two bytes that precede them. The low-order bit of this value will be set if row 0 is really present, the next bit if row 1 is really present, and so on. The two bytes before these flags, labeled ofs₀, store the offset of the first row in the page. This offset is the number of bytes past the end of the page header at which the row itself can be found. So if row 0 begins at the very beginning of the heap, at byte 28 in the page, ofs₀ would have the value 0000.

As more rows are added to the page, space is allocated for them in the heap, and additional index entries are added at the end of the heap, growing backwards. Once there have been sixteen rows added, all the bits in row_pf0 are accounted for, and when another row is added, before its offset entry ofs₁₆ can be added, another row bit-mask entry row_pf1 needs to be allocated, followed by its corresponding pad₁. And so the row index grows backwards towards the rows that are being added forwards, and once they are too close for a new row to fit, the page is full, and another page gets allocated to the table.

Album rows hold an album name and ID along with an artist association, with the structure shown below. The unknown value at bytes 00-01 seems to usually have the values 80 00. It is followed by a two-byte value Mr. Flesniak called index_shift, although I don’t know what that means, and another four bytes of unknown purpose. But at bytes 08-0b we finally find a value we have a use for: artist_id holds the ID of an artist row associated with this track row. This is followed by id, the ID of this track row itself, at bytes 0c-0f. We assume that there are index tables somewhere that would let us locate the page and row index of a record given its table type and ID, but we have not yet found and figured them out.

This is followed by five more bytes with unknown meaning, and the final byte in the row, ofs_name is a pointer to the track name (labeled o_n in the byte field diagram). To find the location of the name, add ofs_name bytes to the address of the start of the track row itself. The name itself is encoded in a surprisingly baroque way, explained in DeviceSQL Strings.

Artist rows hold an Artist name and ID, with the structure shown in Artist row with nearby name or Artist row with far name. The subtype value at bytes 00-01 determines which variant is used. If the artist name was allocated close enough to the row to be reached by a single byte offset, offset, subtype has the value 0060, and the row has the structure in Artist row with nearby name. If the name is too far away for that, subtype has the value 0064 and the row has the structure in Artist row with far name.

In either case, subtype is followed by the unexplained two-byte value found in many row types that Mr. Flesniak called index_shift, and then by id, the ID of this artist row itself, at bytes 04-07, an unknown value at byte 08, and ofs_name_near at byte 09 (labeled o_n), the one-byte name offset used only in the first variant.

If subtype is 0064, the value of ofs_name_near is ignored, and instead the two-byte value ofs_name_far (labeled o_far) is used.

Whichever name offset is used, it is a pointer to the artist name. To find the location of the name, add the value of the offset to the address of the start of the artist row itself. This gives the address of a DeviceSQL string holding the name, with the structure explained in DeviceSQL Strings.

Artwork rows hold an id (which tracks refer to) and the path at which the corresponding album art image file can be found, with the structure shown below. Note that in this case, the DeviceSQL string path is embedded directly into the row itself, rather than being located elsewhere in the heap through an offset. The structure of the string itself is still as described in DeviceSQL Strings.

Color rows hold a numeric color id (which controls the actual color displayed on the player interface) at bytes 05-06 and a text label or name starting at byte 08 which is a DeviceSQL string shown in the information panel for tracks that are assigned the color. The rows have the structure shown below. There are several bytes in the row that are not yet known to have any meaning.

Regardless of the names assigned to the colors by the user, the row id values map to the following colors in the user interface of rekordbox and on CDJs:

Genre rows hold a numeric genre id (which tracks can be assigned) at bytes 00-03 and a text name starting at byte 04 which is a DeviceSQL string. The rows have the structure shown below:

The History menu automatically records playlists of the tracks performed off a particular USB or SD card in a new, numbered playlist each time the media is mounted in a player. These playlists have names like "HISTORY 001". This table lists all the history playlists which have been created for the current database, tying their name to an ID which is used to match the History Entry Rows that make up the playlist for the corresponding performance.

The rows are much simpler than the general-purpose hierarchical playlists described below. They hold only a numeric id at bytes 00-03 and a text name starting at byte 04 which is a DeviceSQL string.

History entry rows list the tracks that belong to a particular history playlist, and also establish the order in which they were played. They have a very simple structure, shown below, containing only three values. The track_id at bytes 00-03 identifies the track that was played at this position in the playlist, by corresponding to the id of a row in the Track table. The playlist_id at bytes 04-07 identifies the history playlist to which it belongs, by corresponding to the id of a row in the History Playlist list. The entry_index at bytes 08-0b specifies the position within the playlist at which this entry belongs.

Key rows represent musial keys. They hold a numeric id (which tracks can be assigned) at bytes 00-03 and a text name starting at byte 08 which is a DeviceSQL string. (There seems to be a second copy of the ID at bytes 04-07.) The rows have the structure shown below:

Label rows represent record labels. They hold a numeric genre id (which tracks can be assigned) at bytes 00-03 and a text name starting at byte 04 which is a DeviceSQL string. The rows have the structure shown in Genre or Label row, above.

Playlist tree rows are used to organize the hierarchical structure of the playlist menu. There is probably an index somewhere that makes it possible to find the right rows directly when loading a playlist, but we have not yet figured out how indices work in DeviceSQL databases, so Crate Digger simply reads all the rows and builds its own in-memory index of the tree.

Playlist tree rows can either represent a playlist “folder” which contains other folders and playlists, or a regular playlist which holds only tracks. The rows are identified by an id at bytes 0c-0f, and also contain a parent_id at bytes 00-03 which is how the hierarchical structure is represented: the contents of a folder are the other rows in this table whose parent_id folder is equal to the id of the folder.

Similarly, the tracks that make up a regular playlist are the Playlist Entry Rows whose playlist_id is equal to this row’s id.

Each playlist tree row also has a text name starting at byte 14 which is a DeviceSQL string displayed when navigating the hierarchy, a sort_order indicator at bytes 08-0b (this may be the same value used to select sort orders when requesting menus using the dbserver protocol, shown in the packet analysis, but this has not yet been confirmed), and a value that specifies whether the row defines a folder or a playlist. In the Kaitai Struct, this value is called raw_is_folder, is found at bytes 10-13, and has a non-zero value for folders. For convenience, the struct also defines a derived value, is_folder, which is a boolean.

The rows have the following structure:

Playlist entry rows list the tracks that belong to a particular playlist, and also establish the order in which they should be played. They have a very simple structure, shown below, containing only three values. The entry_index at bytes 00--03 specifies the position within the playlist at which this entry belongs. The track_id at bytes 04--07 identifies the track to be played at this position in the playlist, by corresponding to the id of a row in the Track table, and the playlist_id at bytes 08--0b identifies the playlist to which it belongs, by corresponding to the id of a row in the Playlist Tree.

Tags provide a flexible way for DJs to categorize tracks, supported by the “My Tags” tab within rekordbox. Tags have names, and can be assigned to any number of tracks. Tags themselves can be grouped into categories, which are stored in the same table.

The rows have the following structure:

The first two bytes serve an unknown purpose but their values always seem to be the same. They are followed by tag_index at bytes 02--03 which seems to increment by 20 for each row. This is followed by another eight bytes of unknown purpose that always seem to be zero.

The category at bytes 0c–0f holds the ID of the category to which the tag belongs; if this row is itself a category, this field has the value 0. The category_pos at bytes 10–13 specifies zero-based position at which this tag should be displayed within its category. If the row represents a category rather than a tag, then this is the zero-based position of the category itself within the category list.

The id at bytes 14–17 is how the tag or category is referenced in Tag Track Rows or the category field. Tags seem to have very large id values, while the four categories have fixed id values in the range 1—​4.

The value of raw_is_category at bytes 18–1b is non-zero when this row stores a tag category instead of a tag. It is followed by two bytes of unknown purpose that always seem to have the same values, and a byte that may hold some sort of flags that have not yet been understood.

A variable number of bytes starting at byte 1f is a DeviceSQL string holding the name of the tag or category. Finally, this is followed by a byte with an unknown purpose, whose value always seems to be 3.

These rows establish the relationship between Tags and Tracks.

The rows have the following structure:

The first four bytes have no known purpose and always seem to be zero.

The track_id at bytes 04--07 identifies the Track to which a tag has been assigned. The tag_id at bytes 08--0c identifies a Tag the DJ has assigned to this track.

The final four bytes in the row seem to always have the values shown, and have no known purpose.

Track rows describe audio tracks that can be played from the media export, and provide many details about the music including links to other tables like artists, albums, keys, and others. They have the structure shown below:

The first two bytes, labeled u₁, have an unknown purpose; they usually are 24 followed by 00. They are followed by the unexplained two-byte value found in many row types that Mr. Flesniak called index_shift, and a four-byte value he called bitmask, although we do not know what the bits mean. The value at bytes 08-0b, sample_rate, is the first one we have a solid understanding of: it holds the playback sample rate of the audio file, in samples per second (this will be 0 if it is unknown or variable).

Bytes 0c-0f hold the value composer_id which identifies the composer of the track, if known, as a non-zero id value of an Artist row. The size of the audio file, in bytes, is found in file_size at bytes 10-13. This is followed by an unknown four-byte value, u₂, which may be another ID, and two unknown two-byte values, u₃ (about which Mr. Flesniak says “always 19048?”) and u₄ (“always 30967?”).

If there is cover art for the track, there will be a non-zero value in artwork_id (bytes 1c-1f), identifying the id of an Artwork row.

If a dominant musical key was identified for the track there will be a non-zero value in key_id (bytes 20-23), which represents the id of a Key row. If the track is known to be a remake, the non-zero Artist row id of the original performer will be found at bytes 24-27 in original_artist_id. If there is a known record label for the track, the non-zero value in label_id (bytes 28-2b) will link to the id of a Label row id. Similarly, if there is a known remixer, there will be a non-zero value in remixer_id (bytes 2c-2f) linking to the id of an Artist row.

The field bitrate at bytes 30-33 stores the playback bit rate of the track, and track_number at bytes 34-37 holds the position of the track within its album. tempo at bytes 38-3b holds the playback tempo of the start of the track in beats per minute, multiplied by 100 (in order to support a precision of BPM). If there is a known genre for the track, there will be a non-zero value in genre_id at bytes 3c-3f, representing the id of a Genre row.

If the track is part of an album, there will be a non-zero value in album_id at bytes 40-43, and this will be the id of an Album row. The Artist row id of the primary performer associated with the track is found in artist_id at bytes 44-47. And the id of the track itself is found in id at bytes 48-4b. If the album is known to consist of multiple discs, the disc number on which this track is found will be in disc_number at bytes 4c-4d. And the number of times the track has been played is found in play_count (bytes 4e-4f).

The year in which the track was recorded, if known, is in year at bytes 50-51. The sample depth of the track audio file (bits per sample) is in sample_depth at bytes 52-53. The playback time of the track (in seconds, at normal speed) is in duration at bytes 54-55. The purpose of the next two bytes, labeled u₅, is unknown; they seem to always hold the value 29.

Byte 58, color_id (labeled c_id in the diagram), holds the color assigned to the track in rekordbox, as the id of a Color row, or zero if no color has been assigned. Byte 59, rating (labeled r in the diagram) holds the rating (0 to 5 stars) assigned the track. The next two bytes, labeled u₆, have an unknown purpose, and seem to always have the value 1. The two bytes after them, labeled u₇, are also unknown; Mr. Flesniak said “alternating 2 and 3”.

The rest of the track row is an array of 21 two-byte offsets that point to DeviceSQL strings. To find the start of the string, add the address of the start of the track row to the offset. The purpose of each string is described in the following table. For convenience, the strings can be accessed as Kaitai Struct instance values with the names shown in the table:

The flag byte described above is labeled l_k (lengthAndKind) below. If S (the low-order bit of l_k) is set, it means the string field holds a short ASCII string. The length of such a field can be extracted by right-shifting l_k once (or, equivalently, dividing it by two). This length is for the entire string field, including l_k itself, so the maximum length of actual string data is 126 bytes.

Again the flag byte described above is labeled l_k (lengthAndKind) below. If S (the low-order bit of l_k) is zero, it means the string field holds a long or wide string, whose format is specified by the other flag bits described above, and whose length is determined by a two-byte length field which follows the flag byte:

As always, length represents the length of the entire field including the header bytes, so the length of the actual string data is . We have only ever seen zero values for the pad byte. The encoding of the string data is determined by the flag bits in l_k_ as described above.

When an International Standard Recording Code is present as the first string pointer in a track row, it is marked with kind 90 but does not actually hold a UTF-16-LE string. Instead, the first byte after the pad value following the length is the value 03 and then there are bytes of ASCII, followed by a null byte. Crate Digger does not yet attempt to cope with this.