54 guides on files. Showing the 48 most recent.
Merging, splitting, converting and shrinking documents. These guides say what a conversion actually preserves and what it silently drops, and where a file's limit stops being technical and becomes a legal question about the document itself.
Ranked by how many pages of this site link to them, not by traffic.
Splitting a workbook writes one .xlsx per sheet, named after the tab. It carries the values across and not the formulas — which is the right default when the point is to send one department its own tab.
Daniel Okonkwo · 4 min read
A cell can hold a formula and no cached result. A reader that skips empty cells throws the formula away with them — and says the file has none. One parsing option separates the two cases.
Daniel Okonkwo · 4 min read
OpenDocument makes styles.xml optional. Several readers demand it and reject the whole document without it — "Cannot find file styles.xml in zip" on a file that is not broken.
Daniel Okonkwo · 4 min read
JSON takes your header text as a key exactly as written. XML cannot — its names may not hold spaces, parentheses or a leading digit — so they are normalised, and knowing how prevents a surprise downstream.
Daniel Okonkwo · 4 min read
Whitespace is the whole reason these tools exist. A row of blanks looks empty, is not empty to a strict test, and quietly survives every filter you apply after it.
Daniel Okonkwo · 4 min read
Twelve monthly reports can become twelve tabs or one table of twelve months. Only the second can be sorted and summed in one go — and it is the one where the header rows need handling.
Daniel Okonkwo · 4 min read
Course timetables, match fixtures, shift rotas and conference programmes all start life as a table. Four columns are enough to turn one into a file every calendar application can import.
Daniel Okonkwo · 4 min read
2.1 marks types without an equals sign, 3.0 is what everything reads, 4.0 writes some values as URIs — so a phone can arrive as tel:+33612345678, prefix included. Knowing which you have explains most import surprises.
Daniel Okonkwo · 3 min read
A contact can have several phone numbers and several addresses. The CSV joins them with a middle dot into one cell; the JSON keeps them as a list, which is the difference between a script that works and one that splits on a guess.
Daniel Okonkwo · 3 min read
Same file, same parser, two outputs. The spreadsheet gets eight columns; the JSON gets the named time zone, the all-day flag and the recurrence rule as well.
Daniel Okonkwo · 3 min read
No stylesheet, no script, layout built from nested tables and styles written on every single tag. Knowing why explains what an exported HTML file will and will not look like.
Daniel Okonkwo · 3 min read
The header row is matched in six languages, so prénom, apellidos, Vorname and cognome are all understood. One header is genuinely ambiguous — nom — and it is settled by the column next to it.
Daniel Okonkwo · 4 min read
Names, addresses and organisations are structured fields in a vCard. Flatten them into a spreadsheet and they read identically while losing the seams — which matters the moment you build a vCard back out of that spreadsheet.
Daniel Okonkwo · 4 min read
The merge tools put every record from every file into one output, in the order you gave them. That is the right default and the one thing to know before you feed in two exports of the same account.
Daniel Okonkwo · 4 min read
An .mbox is one enormous file your operating system cannot search. Turn it into .eml files and every message becomes something your machine indexes, your mail client opens and you can delete one at a time.
Daniel Okonkwo · 3 min read
Mail headers are allowed to carry ASCII only, so an accented subject is encoded before it travels. Two encodings are in use, both start with =?, and decoding them is the whole difference between a readable message and a wall of symbols.
Daniel Okonkwo · 3 min read
iCalendar writes a start time in one of three ways, and only one of them is unambiguous. A meeting written with a named zone, converted on machines in Paris, New York and Honolulu, spanned nineteen hours and changed day.
Daniel Okonkwo · 4 min read
An .ics file stores a weekly meeting once, with a rule attached. Export it to CSV and you get a single row for the whole series — which is the file being honest, not the converter losing rows.
Daniel Okonkwo · 5 min read
One file, thousands of messages, separated by a line beginning From. The format has one famous weakness, and it is the reason a message can lose its ending without anything reporting an error.
Daniel Okonkwo · 4 min read
Mail carries files as text, three bytes written as four characters. A 10 MiB attachment occupies 13.68 MiB of the message, which is why a 25 MB limit really means about 18 MiB of files.
Daniel Okonkwo · 4 min read
A saved message is a text file you can read anywhere. The catch is that opening it in something that loads remote images announces the moment you did — which is what a tracking pixel is for.
Daniel Okonkwo · 5 min read
Deduplication compares whole rows exactly, cell type included. Five identical-looking rows came out as three, because one held a number, one a string and one a string with a leading space.
Daniel Okonkwo · 4 min read
A spreadsheet file stores both the formula and the last answer Excel computed. Stripping the formula leaves the stored answer — and leaves a blank wherever the file never carried one.
Daniel Okonkwo · 4 min read
One structural difference explains everything else: TAR does not compress, it only stacks; ZIP compresses each file on its own. Measured on 60 small source files, that is the difference between 1,809 bytes and 14,686.
Daniel Okonkwo · 12 min read
Four extensions, three of them the same box with different lids. Rename an XLSX to .zip and it opens — that single fact explains the whole family, and explains why XLS, which does not, is the one still causing trouble.
Daniel Okonkwo · 12 min read
A PDF carries its metadata twice, in two stores that can tell different stories, and neither of them is the whole story. Here is what is actually in the file, what clearing it removes, and the two things that survive every wipe.
Daniel Okonkwo · 15 min read
Numbering a tidy document is trivial. The cases that bite are a page turned sideways, a Letter sheet among A4 ones, a print file with bleed, and a document that already prints its own number. All four were tested: on the first three the number lands exactly where you asked, and the fourth is not detected at all.
Daniel Okonkwo · 14 min read
A PDF stores glyphs at coordinates — not lines, not paragraphs, not a reading order. Extraction rebuilds the text from those positions, which is why two columns come out interleaved, a table loses its cells, and a scan gives you nothing at all. Measured by running the tool.
Daniel Okonkwo · 15 min read
Scaling until the loudest sample hits a ceiling barely changes how loud something sounds. Measuring in LUFS does. This tool measures — in two passes, correctly — and then prints a result it never verified, which on ordinary material can be well over a decibel adrift.
Daniel Okonkwo · 14 min read
One ffmpeg command, no encoder, and a result whose video stream is byte-for-byte the one you started with — verified by checksum. Plus why the file barely shrinks, and the difference between a silent track and no track at all.
Daniel Okonkwo · 11 min read
There are two completely different ways to turn a video, and only one of them touches the picture. This tool takes the slow, lossy, universal road — and there is a good chance your sideways phone clip does not need it at all.
Daniel Okonkwo · 11 min read
Three commands hide behind three buttons: one frame at a timestamp, a fixed number spread across the clip, or one every N seconds. Here are the exact arguments, the 60-frame ceiling and the reason a frame from the middle of a compressed clip can never be as sharp as a keyframe.
Daniel Okonkwo · 12 min read
Whether a drawn signature is valid is settled elsewhere. What decides whether your document actually gets signed is the order you ask people in, what the audit trail records, and six failure modes that have nothing to do with the law.
Daniel Okonkwo · 18 min read
The last resort when nothing can be compressed further. It works, and it has three sharp edges: the parts are useless on their own, the order is absolute, and the megabyte you set is not the megabyte the limit means.
Daniel Okonkwo · 7 min read
Plain text has no layout, so any converter has to invent one for you. Here is exactly which decisions this one makes — page, margins, font, line breaks — what it does with a tab and a long line, and what you have to add yourself before a note is worth keeping.
Daniel Okonkwo · 19 min read
Three completely different faults hide behind the same sentence. One is the encoding, one is the separator, one is Excel guessing at types while it opens the file — and the fix for each is different. Here is how to tell them apart in five seconds.
Daniel Okonkwo · 19 min read
That tick at the edit point is not a flaw in the software. It is a step in the waveform, and a step is broadband energy — which is the definition of a click. Here is the arithmetic, measured, and the two places you can put a cut so it never happens.
Daniel Okonkwo · 18 min read
One of these formats stores the samples, one stores the same samples packed smaller, and one stores a guess about what you would have heard. Which conversions between them are free, which are merely expensive, and which are one-way doors — with the arithmetic for each.
Daniel Okonkwo · 15 min read
The soundtrack inside your video has already been through a lossy encoder once. Whether extracting it costs you a second pass depends entirely on which of the three buttons you press — and "extract to MP3", the one everybody reaches for, is the one that costs.
Daniel Okonkwo · 15 min read
A GIF has no real video compression: every frame is a whole picture, capped at 256 colours. That gives you an arithmetic you can do in your head — width times height times frames — and three levers to pull when the upload box says the file is too big.
Daniel Okonkwo · 14 min read
Going from 1080p to 720p does not halve the picture: it removes 56 % of the pixels, and it removes rather less than that of the file. Here is the ladder with real pixel counts, honest bitrates and what three minutes weighs at each rung — plus the reason a low-bitrate source barely shrinks at all.
Daniel Okonkwo · 11 min read
The extension is almost never the real problem. A .mov and a .mp4 are cousins from the same family of file formats, and what actually stops the video is the codec sealed inside it — usually HEVC. Here is how to tell the two failures apart, and when changing the box is enough.
Daniel Okonkwo · 14 min read
The quality slider cannot aim at a file size — that is not what it is for. But the limit and the length of your clip already fix the bitrate you are allowed to spend, and one division tells you whether the resolution you are using can possibly fit.
Daniel Okonkwo · 14 min read
You asked for 1:23 and got 1:21. Nothing is broken: a cut that does not re-encode can only land on a keyframe, and how far away the nearest one is depends entirely on what recorded the video. Here is how to know which you have and when to accept the drift.
Daniel Okonkwo · 7 min read
A duplex scanner that took one side at a time, a stack fed upside down, a page that came out twice. Reordering is not the same operation as extracting pages, and knowing which one you are doing tells you what happens to everything that is not a page.
Daniel Okonkwo · 8 min read
You rotated the scan, saved it, and the recipient still opened it sideways. Nothing is broken — rotation in a PDF is an instruction rather than a change to the page, and instructions can be ignored. Here is when that happens and how to produce a file that cannot be misread.
Daniel Okonkwo · 8 min read
A landlord wants page 3. An accountant wants January. You need to send those pages and not the eleven others, and there is a trap: the obvious way leaves the removed pages inside the file you send.
Daniel Okonkwo · 11 min read
Drawing your name onto a PDF produces a simple electronic signature. European law says that cannot be dismissed just for being electronic — and also that it carries none of the presumptions a qualified signature does. Knowing which tier you have is the difference between a document that holds and one you have to defend.
Camille Laurent · 9 min read