What a Codec Actually Is
Codec stands for coder-decoder. It's the software that decides how video data gets compressed when something is recorded or uploaded, and how it gets decompressed during playback. The compression is everything - raw uncompressed 4K video generates roughly 12 gigabytes per minute. Nobody is streaming that. Codecs make video files small enough to be practical.
The container format - MP4, MKV, MOV, WebM - is a separate thing. Think of the container as the box and the codec as what's inside it. An MP4 file can contain H.264, H.265, or AV1 video. When someone says "download as MP4," they're specifying the box. The codec inside varies based on what the platform encoded it as.
Good codecs work by throwing away visual information you won't miss. Human vision is more sensitive to changes over time than to fine spatial detail, more sensitive to brightness than color, more sensitive to the center of the frame than the edges. Every modern codec exploits all of that.
H.264: The One That Works Everywhere
H.264 (also called AVC or Advanced Video Coding) was finalized in 2003 and spent the 2010s becoming the dominant standard for internet video. It's still the most widely used codec in the world by sheer volume of content, and its main advantage hasn't changed since it launched: compatibility.
Almost every device made in the last fifteen years can decode H.264 in hardware. Phones, tablets, laptops, smart TVs, game consoles, cheap streaming sticks - all of them. Hardware decoding means the video plays without the device getting hot, the fan spinning up, or the battery draining at twice its normal rate. That matters.
Where H.264 loses out is compression efficiency. To match the visual quality that H.265 achieves at a given file size, H.264 needs roughly double the data. Against AV1, it needs about three times as much. That gap is the reason the industry has been moving away from it for high-quality streaming - H.264 is expensive in bandwidth terms for what it delivers. But for downloaded files you want to share with anyone on any device, it's still the safe, sensible choice.
H.265: Better Compression, Complicated Story
H.265 (HEVC, or High Efficiency Video Coding) was supposed to replace H.264 cleanly. It delivers roughly twice the compression efficiency - same visual quality at half the file size, which is a genuinely significant improvement. The problem was licensing.
Unlike H.264, which had relatively straightforward patent licensing, H.265 had multiple overlapping patent pools making conflicting demands on anyone who wanted to implement it. This made it expensive, slowed adoption, and eventually pushed major tech companies including Google, Apple, Amazon, Microsoft, Netflix, and Mozilla to collectively fund a patent-free alternative. That alternative became AV1.
H.265 is broadly supported now, but hardware decoding varies more than H.264. Older devices may fall back to software decoding, which works but consumes significantly more CPU, drains the battery faster, and can cause choppy playback on less powerful hardware. If you download a video that plays fine on your laptop but stutters on an older phone or TV, the codec is often why.
AV1: Where Things Are Heading
AV1 is royalty-free and open. No licensing fees, no patent pools, no legal complications. Any company can implement it without paying anyone. That's why it was funded by basically every major tech company simultaneously - they all had strong financial reasons to want an alternative to H.265.
The compression efficiency gains are real. AV1 achieves the same visual quality as H.265 at roughly 20-30% smaller file sizes, and beats H.264 by around 50%. At equivalent sizes, AV1 video looks noticeably better. For streaming across constrained connections this is a big deal.
YouTube moved to AV1 for high-traffic content starting in 2018 and has expanded significantly since. Netflix encodes its catalog in AV1. TikTok and Facebook both use it for portions of their delivery, particularly in regions where bandwidth is limited and smaller files load faster and more reliably.
The current limitation is hardware decoding support. Devices made before 2020-2021 mostly lack AV1 hardware decoding. Software decoding works, but AV1 is computationally heavier than H.265, so the performance hit on older or weaker devices is noticeable. Snapdragon 888 and newer, Apple A14 and newer, recent Intel and AMD integrated graphics all include AV1 hardware decoders. The installed base is growing fast, and within a couple of years the compatibility gap will largely disappear.
VP9: Briefly, Because It Comes Up
Google's own royalty-free alternative developed before AV1 hit the scene. More efficient than H.264, less efficient than AV1, and widely supported because Google baked it into Chrome and YouTube starting around 2013. A lot of YouTube downloads are in VP9.
It's fine. Broadly compatible, decent quality. Just not where the industry's future investment is going. AV1 supersedes it, and VP9 is more of a transitional technology at this point than a long-term standard.
What Different Platforms Actually Deliver
This matters directly for what codec is in a file when you download it from a platform.
TikTok primarily delivers H.264 for standard quality, with H.265 for higher resolutions on supported devices. The exact codec varies by device, network conditions, and account region. Downloads from MyVideoCity give you the best available stream, which may be either.
Instagram uses H.264 for most content. The platform's heavy compression on upload means the codec is somewhat less of a factor - the quality ceiling is set by their encoding before codec choice even enters the picture.
Facebook has moved toward AV1 more aggressively than most social platforms, particularly for videos getting high traffic and in bandwidth-limited regions. Downloads may be H.264 or AV1 depending on the content.
Vimeo defaults to H.264 for compatibility but provides higher quality options in H.265. Vimeo's compression is significantly lighter than social platforms, so the codec matters more there - the source quality is better preserved, meaning the codec efficiency difference is actually visible.
So Which One Should You Care About?
Honestly, it depends on what you're doing with the file.
Archiving content to watch on modern devices? Prefer AV1 or H.265 where available. Better quality at smaller file sizes, and modern devices handle both without issues.
Editing the footage in video software? H.264 is still the path of least resistance. Most editors handle H.265 now, and AV1 editing support is improving but has gaps in older software. H.264 causes the fewest headaches in post-production workflows.
Sharing with someone on older hardware? Convert to H.264. The compatibility argument is real. A video that won't play is worse than a larger file that will.
Re-uploading somewhere after downloading? The codec choice barely matters. Every major platform re-encodes uploaded video in their own way. You're not gaining anything by uploading AV1 to Instagram - it comes out as Instagram's H.264 on the other side.
Related reading: Video Formats and Quality Guide and How AI Is Changing Online Video.