How to Reduce Video
File Size

Why Video Files Are So Large

Before diving into compression methods, it helps to understand what makes video files large in the first place. Three main factors determine file size:

• Resolution — a 4K frame (3840×2160) contains 4× more pixels than 1080p (1920×1080). More pixels means more data per frame, and at 30 frames per second that adds up fast.
• Bitrate — the amount of data used per second of video. A typical iPhone 4K video records at 50–60 Mbps (megabits per second), which translates to roughly 375–450 MB per minute. A compressed 1080p YouTube video uses only 4–8 Mbps.
• Codec — the compression algorithm used to encode the video. Raw video is enormous (1.5 GB per minute at 1080p). Codecs like H.264 and H.265 compress this by 100–300x, but some codecs are more efficient than others.

Other factors include frame rate (60 fps produces roughly 2x the data of 30 fps), audio tracks (especially multi-channel surround sound), and container format overhead. The good news: you can address each of these factors to dramatically shrink your video.

Method 1: Use an Online Compressor (Easiest)

The fastest way to reduce video file size is to use an online tool like Convertio's video compressor. No software installation needed — upload your video, wait for processing, and download the compressed result.

How it works: Convertio re-encodes your video using H.264 at an optimized quality level. It automatically adjusts the bitrate based on resolution and content complexity, stripping unnecessary metadata and using efficient encoding presets.

Method 2: Reduce Resolution

Lowering the resolution is one of the most effective ways to shrink a video. Resolution determines how many pixels are in each frame, and the relationship between resolution and file size is roughly proportional to the pixel count.

Downscaling from 4K to 1080p reduces the pixel count by 75%, resulting in a file that is typically 60–75% smaller. Going from 1080p to 720p cuts another 40–55%. For most viewing scenarios — watching on a phone, sharing on social media, or embedding on a website — 720p is perfectly adequate.

Method 3: Lower Bitrate / CRF

Bitrate is the single biggest factor in video file size. There are two ways to control it:

• Constant bitrate (CBR) — every second of video uses the same amount of data, regardless of scene complexity. Simple to predict file size, but wastes data on simple scenes and starves complex ones.
• Constant Rate Factor (CRF) — a quality-based approach where the encoder allocates more data to complex scenes and less to simple ones. This produces better visual quality at a given file size. CRF is the recommended method for file-size reduction.

For H.264, the CRF scale goes from 0 (lossless) to 51 (worst quality). The default is 23. Practical range:

Each +6 CRF roughly halves the file size. So moving from CRF 18 to CRF 28 reduces the file to approximately 25% of the original — a 4x reduction with quality that is still perfectly watchable on phones and laptops. CRF 32 pushes further into visible artifact territory but can be useful for previews or when file size is the top priority.

Method 4: Trim / Shorten Duration

This is the most overlooked method: cut out the parts you don't need. Video file size is directly proportional to duration — a 2-minute clip is half the size of a 4-minute one at the same settings.

Common scenarios where trimming helps:

• Recording started early or ended late — trim the dead time at the beginning and end
• Long meeting or lecture recording — extract only the relevant segment
• Screen recording with setup/cleanup time — remove the preparation footage
• Social media posts — Instagram Reels (90s max), TikTok (10 min max), Twitter/X (2:20 max)

You can use Convertio's video trimmer to cut your video online before or after compression. Trimming does not require re-encoding when done correctly (lossless cut), so there is zero quality loss.

Method 5: Convert to Efficient Format (MP4 H.264)

If your video is in an older or less efficient format, converting to MP4 with H.264 codec can dramatically reduce file size without any settings tweaks:

H.264 is the gold standard for compatibility and compression efficiency. It plays on every device, browser, and platform without codec issues. For even smaller files, H.265 (HEVC) offers 25–50% better compression but is not universally supported yet.

Method 6: FFmpeg Command Line (Full Control)

For maximum control over compression, FFmpeg is the industry-standard command-line tool. It is free, open-source, and runs on Windows, macOS, and Linux.

Basic Compression

Compress a video to H.264 at CRF 28 (good quality, small size):

ffmpeg -i input.mov -c:v libx264 -crf 28 -preset slow \
    -c:a aac -b:a 128k -movflags +faststart output.mp4

Compress + Downscale to 720p

Combine CRF compression with resolution reduction for maximum savings:

ffmpeg -i input.mov -c:v libx264 -crf 28 -preset slow \
    -vf "scale=-2:720" -c:a aac -b:a 128k \
    -movflags +faststart output_720p.mp4

The scale=-2:720 filter resizes to 720p height while keeping the aspect ratio. The -2 ensures the width is divisible by 2 (required by H.264).

Target a Specific File Size

To fit a 5-minute video into 25 MB (for email), calculate the required bitrate:

# Target: 25 MB for 300 seconds
# Video bitrate = (25 * 8 * 1024 / 300) - 128 = ~555 kbps
ffmpeg -y -i input.mov -c:v libx264 -b:v 555k -pass 1 -an -f null /dev/null
ffmpeg -y -i input.mov -c:v libx264 -b:v 555k -pass 2 -c:a aac -b:a 128k output.mp4

Two-pass encoding analyzes the video first, then distributes the bitrate optimally across the entire file. This produces much better quality than single-pass when targeting a specific file size. On Windows, replace /dev/null with NUL. The -y flag skips overwrite prompts during the first pass.

Useful FFmpeg Flags

Compression Results: Real-World Comparison

Here is what to expect when compressing a typical 1-minute 4K video (iPhone 15, 60 fps, HEVC) using each method:

The sweet spot for most people is 1080p at CRF 28: a 93% reduction from 4K source while maintaining quality that looks great on any screen. For email attachments, 720p at CRF 28 fits most videos under 25 MB.

Platform-Specific Instructions

Windows

• Online (easiest): Open convertio.com/compress-video in any browser and upload your file.
• HandBrake (free): Download from handbrake.fr. Open your video, set the Quality slider to RF 28, choose a Preset (Fast 1080p30 or Fast 720p30), and click Start Encode.
• VLC: Media → Convert/Save → select file → choose Video - H.264 + MP3 (MP4) profile. Adjust bitrate in the wrench icon settings.
• FFmpeg: Download from ffmpeg.org/download.html. Use the commands from the FFmpeg section above in Command Prompt or PowerShell.

macOS

• Online: Use Convertio's video compressor in Safari or Chrome.
• HandBrake: Same as Windows — available for macOS with the same UI and settings.
• iMovie: Import your video, then File → Share → File. Choose resolution (720p or 1080p) and quality (Medium or Low) to reduce size.
• FFmpeg: Install with brew install ffmpeg, then use the terminal commands above.

iPhone

• Online: Open convertio.com/compress-video in Safari. Tap Choose Video and select from your Camera Roll. Works without installing any app.
• Prevent large files: Go to Settings → Camera → Record Video and choose 1080p at 30fps instead of 4K. This alone reduces file size by 60–75%.
• Shortcuts app: Create a shortcut with the "Encode Media" action. Set format to H.264, resolution to 1080p. Run it from the Share Sheet on any video.

Android

• Online: Open convertio.com/compress-video in Chrome. Tap Choose Video and select from your gallery.
• Camera settings: Open your Camera app → Settings → Video resolution and select 1080p or 720p instead of 4K.
• Telegram trick: Send the video to yourself in Telegram as a "file" (not a video message). Telegram compresses videos to ~720p before sending, and you can then save the compressed version.

Which Method Should You Use?

Additional Tips for Smaller Videos

• Use the -preset slow flag in FFmpeg. Slower encoding presets produce smaller files at the same visual quality. The slow preset is the best balance — veryslow saves only 2–3% more but takes much longer.
• Remove audio if not needed. Audio can add 10–15% to file size. For silent screen recordings, memes, or decorative backgrounds, use -an in FFmpeg or uncheck audio in HandBrake.
• Reduce frame rate from 60fps to 30fps. Unless your video contains fast motion (gaming, sports), 30fps is visually equivalent and roughly halves the data compared to 60fps.
• Avoid re-compressing already compressed video. Compressing an already-compressed H.264 file again introduces generation loss without significant size reduction. If your source is already well-compressed, focus on resolution and duration changes instead.
• Use H.265 for storage. If you do not need maximum device compatibility (e.g., archiving on your own drives), H.265 produces 25–50% smaller files than H.264 at the same visual quality.