Find out why the video is heavy
Open Video properties with your recording and read the duration, resolution, frame rate and average bitrate. Size depends mostly on duration and bitrate: a minute of 4K footage weighs far more than a minute at 720p. Write down the original size, because you will compare the result against it. Messaging apps and email providers set their own limits, and those limits change, so check the current limit of the service you will use rather than relying on a number you remember. If the video is only slightly above the limit, a light compression may be enough; if it is several times larger, you will probably combine two steps.
Compress with a balanced level first
Compress video offers light, balanced and maximum levels and an optional maximum resolution. Start with balanced, because stronger compression removes detail, creates blocks in moving areas and can blur small text. The final size depends on how much movement the recording contains, so the tool cannot promise a number of megabytes. If the result is not smaller than the original, the tool tells you and offers no download; try a stronger level or lower the resolution. Watch the finished file on the device that will receive it, paying attention to faces, lettering and fast movement before you send it.
Lower the resolution when the screen is small
Change video resolution reduces the shorter side to 1080, 720, 480 or less and calculates the other side to keep the proportions. A video watched on a phone rarely benefits from more than 720p, so this is often the biggest saving with the least visible loss. In the 480 by 270 pixel sample, choosing 240p produces 426 by 240 pixels, because codecs need even dimensions. The tool does not enlarge a video that is already small. Resize first or compress first, but not both blindly: change one thing, check the result, then decide whether another step is necessary.
480 × 270 → 426 × 240 MOV → WebM
Convert MOV to MP4 when an app rejects the file
Phones and cameras often save MOV files. Many applications accept them, but some forms, older players and editing tools prefer MP4. Convert video offers MP4, WebM, MOV and MKV. When the existing tracks are compatible, the tool can keep them; otherwise it re-encodes with what your browser can produce. Changing the container does not by itself make a file smaller or guarantee compatibility everywhere, so test the result in the application that rejected the original. Keep the original recording until the converted copy has been played from beginning to end and the sound is confirmed.
Check the final file before sending
Open Video properties again on the new file and compare duration, resolution and size with your notes. The duration should match; the size should be lower. Play the video completely with sound, because problems often appear only in the last seconds. Rename the file clearly, for example with the destination and the date, so you do not send the wrong version. Processing stayed on your device, but the message you send does not: sending the video shares it with the service and the recipient, so remove anything private from the picture and the sound first.
Make a smaller phone-sized copy
Download sample-video.mp4 and open Video properties to note its size and its 480 by 270 pixel resolution. In Compress video choose balanced, MP4 and a maximum of 240p, process it and save the result. Then open Convert video with the original, select WebM, process and compare sizes. Open Video properties for each result.
480 × 270 → 426 × 240 MOV → WebM
The compressed copy measures 426 by 240 pixels and keeps roughly six seconds with sound. The WebM copy keeps the original dimensions in a different container.
Compare the file sizes in your saved files, not only on screen, and play each copy. This sample is tiny and a real recording will behave differently; the exercise shows the process, not a guaranteed saving. If a format is unavailable in your browser, read the message and choose MP4.