Shrink a video for email, messaging, and social posts

Getting a video under an attachment or upload limit is one of the most common reasons people reach for a compressor. The limits themselves are usually fixed: most webmail providers cap attachments somewhere around 25 MB, messaging apps often want clips well under that, and social platforms each have their own ceiling. The good news is that hitting a target size is mostly a matter of applying the same few steps in the right order.

Why the order matters

You can shrink a file four ways: trim footage, lower the resolution, raise the CRF (lower the quality), and shrink the audio. Each one costs you something different. Trimming costs you nothing, because you are removing footage you did not want anyway. The other three trade visible or audible quality for size.

So the rule is simple: do the free thing first, then the steps that hurt least. Most people reach for resolution first and end up with a smaller file that also looks soft. Done in the right order, you usually get a smaller file that still looks fine.

Step 1: trim the parts you do not need

Before touching quality, cut anything that is not earning its place. Intros, walk-up footage, long pauses, and “is it recording?” moments all add weight for nothing. Trimming is the only step that improves the result instead of trading quality for it, so it should always go first.

If your clip has a clear start and end, trim first even if you think it is already short. A surprising amount of phone footage has trailing seconds that add up across many clips.

Step 2: cap the resolution

Phone and screen footage often arrives at 1080p or 4K, which is more than most casual sharing needs. Capping the resolution at 720p or 480p cuts a lot of weight, and on a phone screen the difference is often invisible.

The mistake is going straight to 480p for everything. If the clip will ever be watched on a laptop, 720p is the safer cap: small enough to trim serious size, big enough that faces and text stay readable. Reach for 480p only when the destination is genuinely tiny or the limit is very tight.

Step 3: raise the CRF

Once the resolution is capped, the quality slider is the main size dial. In DivXpress that slider maps to the CRF value the encoder uses, with higher values meaning a smaller file and slightly lower quality.

A balanced setting (around CRF 26) is the right starting point. From there, nudge toward “smaller file” until you either hit your target size or notice the quality drop more than you want. For short clips shared for quick viewing, a CRF in the high 20s to low 30s is usually fine. For anything with fine text or faces that people will look at closely, stay closer to the balanced end and find the size elsewhere.

Step 4: shrink the audio

Audio is a smaller share of the file than video, but it is easy money. A 160 kbps AAC track is already lean, and dropping to 128 kbps or 96 kbps is usually inaudible for voice and casual content. For music you care about, leave it alone; for talking, screen recordings, and ambient sound, lowering the audio bitrate costs little and saves a bit more.

Step 5: check and iterate

Read the size of the output. If you are still over your target, raise the CRF one notch or drop the resolution a step and run again. Because the encode happens on your device rather than uploaded to a queue, iterating is fast and free.

A few platform notes

The exact limits change over time, but the broad shape is stable.

• Webmail attachments (Gmail, Outlook, Yahoo) generally top out around 25 MB. For anything bigger, the standard move is to upload the file and send a link, but a quick compress will get many clips under that line.
• Messaging apps (WhatsApp, Signal, Telegram) usually want clips smaller than email allows. They also often re-encode on their end, so giving them an already-small file avoids a second round of quality loss.
• Chat platforms (Slack, Discord free tier) typically cap uploads around 25 MB. Discord in particular is strict about the free limit.
• Social platforms (Instagram, TikTok, X, YouTube) each re-encode uploads, so the goal is to get under their limit and let them do the final encoding. A clean 720p H.264 MP4 with a CRF in the high 20s is a safe starting point for most of them.

When in doubt, target well under the limit rather than right at it. Limits are usually measured in whole-file bytes, and a file that is exactly at the edge sometimes gets rejected for being a few bytes over.

The short version

• Trim first. It is the only step that costs nothing.
• Cap resolution at 720p for casual sharing, 480p only when you must.
• Use the quality slider (CRF) as the main size dial, starting around balanced and nudging smaller.
• Drop the audio to 128 kbps or 96 kbps for voice and casual content.
• Iterate. Run it, check the size, adjust one thing, run again.

You can run the whole sequence in the compress-video tool without uploading anything. For the background on why CRF matters more than resolution, the guide to how video compression works goes deeper.