Does AV1 really produce smaller files than VP9?

That is the general tendency; because AV1 uses newer and more advanced compression techniques it typically produces a smaller file at the same visual quality. But the size of that difference varies with the content, the resolution and the quality setting you choose, so it would not be right to give a fixed ratio. The gap can be more pronounced in plain scenes with little motion, while in complex, noisy footage the distance between them can narrow. If you want to see the real difference on your own file, the most reliable method is to try a short excerpt with each codec separately and compare the sizes.

Why is AV1 encoding so slow?

The small files AV1 produces come from the encoder evaluating far more possibilities for every frame. There is a direct trade-off between compression efficiency and computational load; better compression means more analysis. That is why encoding the same video with AV1 takes markedly longer than with VP9. On long, high-resolution files that difference becomes measurable in minutes.

Which one should I pick so that more people can watch the video?

Because VP9 has been in use longer, its browser and device support is more established. AV1 support is expanding rapidly, but as it is a newer codec it can fall back to a software decoder, particularly on older devices and some hardware; that increases battery drain and processor load. If your audience is varied and includes older devices, VP9 is the safer choice. The most robust approach, though, is to produce the same video with both codecs and let the browser pick the one that suits it.

Does the codec choice change the quality loss?

Because re-encoding takes place in both cases, some loss is unavoidable; the codec choice does not change that fact. What it does change is how much quality you can preserve at a given file size. AV1 can usually preserve more detail at the same size, or hold the same quality in a smaller file. But if you use a sufficiently generous quality setting you can get results that are hard to tell apart by eye with either codec.

VP9 or AV1 for WEBM Conversion? An Honest Comparison

What the decision is actually about

You have decided to convert your MOV file to WEBM. Now a second question comes up: which codec should the video inside be compressed with?

Let us clear something up first, because this is generally where the confusion starts. WEBM is a container — the box the file comes in. VP9 and AV1 are codecs, that is, the algorithms that compress the picture. WEBM can carry either of them. So saying "I picked WEBM" does not mean you have picked the codec inside.

This decision determines how long the conversion takes, how much space the file occupies and how many people can watch the video without trouble. Let us look at three axes one by one.

Axis 1: Compression efficiency

The tendency here is clear: AV1 is generally more efficient. AV1 is a codec developed later than VP9 and it uses more advanced compression techniques. As a result it typically produces a smaller file at the same visual quality target. Or, looked at the other way round: it can preserve more detail at the same file size.

But it would not be honest to give a definite ratio for the size of that difference. The gain varies with the type of content. In footage with little motion, dominated by plain, flat areas, AV1's advantage is more pronounced. In heavily moving, noisy or highly detailed scenes the distance between them can narrow. The resolution and the quality setting you choose also affect the outcome.

If you are curious about the real difference on your own file, the most reliable method is this: take a representative one-minute excerpt of the video, encode it with both codecs, and compare the resulting sizes and pictures. Look at data from your own content rather than at general ratios.

Ahead on this axis: AV1.

Axis 2: Encoding time

Here the picture reverses, and the difference is at least as pronounced as the first one.

AV1 encoding is markedly slower. This is not a defect, it is the direct price of the first axis. The small files AV1 produces come from the encoder evaluating far more possibilities for every frame. There is a direct trade-off between compression efficiency and computational load: a better result means more analysis.

In practice this means the following: a job that finishes in a few minutes with VP9 can take considerably longer with AV1. On long, high-resolution files that difference turns into a concrete waiting time.

Remember in any case that the move from MOV to WEBM is a re-encode in every situation — because WEBM can carry neither H.264 nor ProRes, the picture necessarily has to be decoded and compressed from scratch. So the time is long to begin with; choosing AV1 lengthens it further.

Ahead on this axis: VP9, by a clear margin.

Axis 3: Breadth of support

VP9 has been in the field longer and that gives it the advantage of maturity. Browser support is established, and hardware decoding support is spread across a wider range of devices.

AV1 support is expanding rapidly and its position on new devices improves with every passing year. Being a newer codec carries a risk, though, particularly on older devices: if there is no hardware support, the decoding work falls to the processor. That can mean the video drains more battery, the device heats up, and playback stutters on low-powered devices.

There is a distinction to watch out for here: a codec being "supported" and being "supported in hardware" are different things. The video may play, but if the battery melts away quickly the viewer's experience is still poor.

Ahead on this axis: VP9.

Decision guide

Pick VP9 if:

You need to finish the conversion in a reasonable time
Your audience is varied and includes older devices
Your share of mobile viewers is high and battery drain matters
You are not sure — VP9 is the safe default choice

Pick AV1 if:

File size is your first priority
The video will be watched a great deal and bandwidth cost is a serious line item
You have time to wait for the encoding
Your audience predominantly uses current devices

Produce both if: You are publishing the video on your own website and can manage it technically — this is the most robust route. The HTML video tag lets you define more than one source; the browser picks the first one it can support. Visitors who support the AV1 version get the small file, those who do not fall back to VP9. The cost of this is encoding twice and hosting two files.

What neither codec can change

Whichever one you pick, two facts stay constant.

There will be re-encoding loss. Because the list of codecs WEBM accepts does not intersect at all with the contents of a MOV, the picture is decoded and compressed from scratch. If the source was already compressed, this is a second round of culling and it cannot be undone. The codec choice does not change that fact, it only changes how much quality you can preserve at a given size. Using a generous quality setting makes more difference than the codec choice.

You should keep the original. If you need another format later, start from the original MOV file rather than from the WEBM output. Otherwise the losses stack up and accumulate. When using our MOV to WEBM converter, let your source always be the original file.

Two decisions that make more difference than the codec choice

There is a fact that gets overlooked while making this comparison: the difference between VP9 and AV1 is often secondary next to two other decisions.

First: resolution. Do you genuinely need 4K in a video you are publishing for the web? Whichever codec you pick, reducing the resolution makes a far bigger difference to file size and encoding time than the codec preference does. Most viewers will not notice they are watching a presentation recording or a product demo at a lower resolution, but they will feel that the page opens quickly.

Second: the quality setting. How generous you are with the encoder is more decisive than which codec you use. AV1 encoded with a stingy setting can look worse than VP9 encoded with a generous one. Especially if you are starting from an already compressed source — and the H.264 inside a MOV is exactly that — you need to leave the encoder room to breathe on the second compression.

The practical recommendation is therefore this: set the resolution and quality correctly first, and think of the codec preference as fine tuning after that. Trying a few settings on a short test excerpt and comparing the result with your own eyes is more reliable than any general advice.

In summary

The choice between VP9 and AV1 is a trade-off between compression efficiency on one side and encoding time and breadth of support on the other. AV1 gives a smaller file at the same quality but encodes markedly more slowly and its support is newer. VP9 finishes faster, works without trouble across a wider range of devices and is efficient enough in most scenarios. For a heavily watched video where you are wrestling with bandwidth costs, AV1's waiting time may pay for itself; for everyday jobs and a mixed audience, VP9 is still the smart default choice.