A file will not play on your television, or it is twice the size you expected, and the answer is one field. The filename is not that field.
Working out whether a video is H.264 or H.265 takes two seconds if you look in the right place, and produces a confident wrong answer if you look at the name.
How to tell if a video is H.264 or H.265
Read the container. Every video file declares the codec of each track in its structure, and that declaration is what a player uses.
Our codec and bitrate checker reads it in the browser without uploading anything, and reports both names because the industry never settled on one. Desktop MediaInfo, VLC's codec information panel and ffprobe all read the same field and will agree with each other.
What none of them read is the filename, which is where most people look first.
Why the filename lies about the codec
A filename is text somebody typed. Renaming a file does not touch a byte of its contents.
In practice, names get written by whoever repackaged a file rather than whoever encoded it, and they get copied between files, edited by hand, and left behind after a conversion. A clip called something.x265.mkv is regularly plain H.264, and the reverse happens just as often.
Reading the codec out of the file is far more reliable, though it is worth knowing that container fields are still written by software rather than measured. Our piece on whether video metadata can be faked covers which fields hold up and which do not.
The same applies to the extension, with an extra wrinkle. MP4 and MKV are containers, not codecs — boxes that can hold almost anything. An MP4 might contain H.264, HEVC, AV1 or several others, which is why the extension tells you about the shape of the box and nothing about the contents. There is more on that distinction in our explainer on video metadata.
The AVC and HEVC naming confusion, resolved
Two standards bodies developed these formats together and each kept its own name, which is why every tool seems to disagree.
H.264 and AVC are the same thing. H.264 is the ITU name, Advanced Video Coding is the MPEG name, and the documents were published jointly. A container storing the codec writes AVC, so that is what a reader reports.
H.265 and HEVC are the same thing, on exactly the same pattern. High Efficiency Video Coding, published jointly, stored as HEVC.
Neither name is more correct. We show both because you searched for one and the file says the other, and picking a side would only move the confusion.
The x264 versus H.264 difference, which is not the same question
This one catches even experienced people, because it looks like another naming quirk and is not.
H.264 is a standard describing what a valid bitstream looks like. x264 is a specific program that produces one. Several encoders produce valid H.264 — x264, hardware encoders in phones and graphics cards, broadcast equipment — and they differ substantially in quality at the same bitrate.
So the encoder field is a separate and genuinely useful reading. It is where names like x264 and x265 live, when the muxer bothered to record them, and our video metadata viewer prints that string beside the codec so you can read both at once. A file encoded by a phone's hardware encoder and a file encoded by x264 are both H.264 and will not look alike at the same size.
An empty encoder field is common and means only that the tool stayed anonymous.
Which devices cannot play HEVC, and why it is not the codec's fault
HEVC compresses better and is fussier about what will play it.
The reason is hardware. Decoding video efficiently needs dedicated silicon, and a device either has an HEVC decoder or it does not. Software decoding technically works and drains a battery in an hour, so most devices simply refuse. Licensing has kept HEVC out of some browsers entirely.
The practical list changes constantly, so we will not publish one that ages badly. The pattern holds: older smart TVs, budget Android handsets, some set-top boxes and a few browsers. Anything from the last few years generally copes.
The profile matters as much as the codec. High 10 means 10-bit colour, and plenty of devices that handle ordinary H.264 refuse High 10 specifically. If a file plays everywhere except one screen, check the profile before you re-encode anything. When you do need to change it, our video format converter handles the job.
Choosing between them for your own work
Two questions decide it, and neither is about quality.
Who has to play this? If the answer includes anyone else's device, H.264 remains the safe choice. Nothing made in the last fifteen years refuses it.
Where is it going to live? Archive footage on a drive you control benefits from HEVC, because the space saving compounds and you control the playback.
One thing not to do is convert an existing H.264 file to HEVC hoping it will look better. Every conversion decodes and recompresses, so the best possible outcome is looking the same while taking less space. Detail lost in the first encode does not come back.
If space is the actual problem, compressing the video directly is usually the better route.
Check the file rather than the name
Two seconds of reading the container beats an hour of re-encoding into a format you already had. Check before you convert, before you send a file to someone with an unknown device, and before you conclude a codec is at fault.
While you are there, the frame rate mode is worth a look — a variable frame rate check catches the timing problem that quietly ruins long edits, and it is a completely separate failure from anything the codec does. And if the concern is what the file reveals rather than how it plays, whether videos store GPS is the place to look next.