To compare approaches to resize video, focus on whether you want the original aspect ratio preserved inside a bounding box or an exact width and height regardless of distortion. The two practical approaches available in most browser-based resizers are Fit, which preserves the source aspect ratio and scales the picture down to fit inside a width and height you enter, and Stretch, which uses the exact width and height you enter and can intentionally distort the picture. A third, less common approach is cropping, but cropping removes pixels rather than resizing them, so it changes the framing instead of the pixel dimensions. Choosing between Fit and Stretch is the core decision, and the right choice depends on where the video will play, how strict the destination is about aspect ratio, and whether letterboxing or stretching is acceptable. Both approaches in browser-based tools re-encode the video into a WebM file at up to 1920 pixels on a side, and both keep the source on your device rather than sending it to a server.
What Resizing a Video Actually Means
Resizing a video means changing the pixel dimensions of each frame. When the picture becomes smaller, the encoder is asked to draw fewer pixels per frame. When the picture becomes larger, the encoder has to invent pixels, which usually softens the picture instead of adding real detail. Because of that, resizing is typically used to make a video smaller rather than larger, and the source needs to already be at or above the target size for the resize to add any value.
Two terms come up constantly when comparing approaches: aspect ratio and bounding box. The aspect ratio is the proportional relationship between width and height, expressed as something like 16:9 or 9:16. A bounding box is the maximum width and height you allow the output to occupy. The Fit approach uses the width and height you enter as a bounding box and keeps the source ratio inside it. The Stretch approach ignores the source ratio and forces the output to match the exact width and height you enter.
The Two Resize Approaches Side by Side
The clearest way to compare the two main approaches is to put them in a table and look at the same properties side by side. Both approaches are available in the Video Resizer, and the same source file can be processed twice to show the difference in the output.
| Property | Fit (aspect-preserving) | Stretch (exact dimensions) |
|---|---|---|
| Aspect ratio | Preserved from the source | Forced to the requested width and height |
| Treats width and height as | A bounding box | Exact output dimensions |
| Scale factor used | The smaller of width scale and height scale | Independent scales for width and height |
| Cropping | Never crops | Never crops |
| Distortion | No distortion | Can distort the picture |
| Best for | Strict aspect-ratio destinations and social feeds | Fixed canvases, thumbnails, banners, and grids |
| Output dimensions | Rounded down to even numbers inside the box | Rounded down to even numbers at the exact size |
Reading down the table, the most important contrast is the third row. Fit applies one scale factor to both axes, while Stretch applies a different scale factor to each axis. That single difference is what causes Stretch to distort and Fit not to, and it is the cleanest way to keep the two approaches straight when you are comparing them for a specific job.
When Fit Wins and When Stretch Wins
Fit wins whenever the destination will not tolerate distortion or wrong proportions. Most social platforms fall into this category. Vertical 9:16 reels, square 1:1 feed posts, and 16:9 landscape players all assume the source already matches their ratio. When it does not, the player either letterboxes the picture with black bars or rejects the upload. Fit solves this by scaling the picture down until it fits inside a 1080×1920 box without changing the ratio.
Stretch wins when the destination has a fixed canvas and you want the picture to fill it edge to edge, distortion and all. A horizontal banner that must be exactly 1920×600, a thumbnail strip where every cell is exactly 320×180, or a collage grid where each slot is the same size are all common cases. Stretch is also a deliberate creative choice in stylized video where the look depends on the distortion rather than fights against it.
A quick numeric example makes the difference concrete. Take a 1920×1080 source and ask for a 1280×800 box in Fit mode. The width scale is 1280 ÷ 1920 = 0.6667. The height scale is 800 ÷ 1080 = 0.7407. Fit picks the smaller scale, so it uses 0.6667. The output is 1920 × 0.6667 = 1280 wide and 1080 × 0.6667 = 720 tall. The output fits inside the 1280×800 box with empty space above and below, and the aspect ratio matches the source. If the same 1920×1080 source goes through Stretch with 1280×800 entered, the output is exactly 1280×800 and the picture is visibly squashed vertically.
For platform-specific targets where the ratio matters and you want to keep the full picture without cropping, the Fit approach is the same one used in the Instagram no-crop resizing workflow.
Limits Shared by Both Resize Approaches
Both Fit and Stretch in browser-based resizers share the same input limits, output format, and processing model. These limits apply no matter which approach you pick, so they belong on the comparison table alongside the per-approach differences.
| Property | Value or behavior |
|---|---|
| Maximum width or height in output | 1920 pixels |
| Minimum width or height in output | 2 pixels |
| Odd dimension handling | Rounded down by one pixel to land on an even value |
| Source size cap | 500 MiB |
| Source length cap | 5 minutes |
| Source maximum per side | 4096 pixels |
| Source maximum area | 3840 × 2160 pixels |
| Output container | WebM |
| Output codecs | VP9 or VP8 video, plus browser-exposed audio |
| Encoding speed | Real-time re-encode in the browser tab |
| Processing location | Local browser tab using canvas captureStream and MediaRecorder; the file does not upload |
| What can change vs the source | Quality, bitrate, frame timing, audio layout, color metadata, and file size |
Two consequences follow from this table. Real-time encoding means the resize takes about as long as the video plays, so a 3-minute clip needs around 3 minutes to finish. The output is a freshly re-encoded WebM, not a metadata rewrite, so the bitrate and quality are set by the browser encoder rather than copied from the source.
How to Compare Approaches to Resize Video in Your Browser
Comparing the two approaches side by side means running the same source through both modes and looking at the resulting files. The Video Resizer accepts MP4, WebM, MOV, M4V, and Ogg sources up to 500 MiB and five minutes long, and exposes both Fit and Stretch modes against the same width and height inputs.
- Open the Video Resizer in a fresh browser tab and pick a local source file from MP4, WebM, MOV, M4V, or Ogg. Wait for the browser to finish reading the file metadata before continuing.
- Enter the same maximum width and height you want to test, for example 1280 and 800. These numbers act as the bounding box for Fit and the exact output for Stretch.
- Select Fit first, choose Resize video, and keep the tab open during the real-time encode. Download the resulting WebM and label it as the Fit version.
- Reopen or reset the tool with the same source file and the same width and height, then switch the mode to Stretch. Choose Resize video again and download the second WebM.
- Open both files side by side. The Fit file will keep the original ratio and may sit inside the requested box with empty space on one axis. The Stretch file will match the box exactly and may look wider or taller than the source.
If the comparison is for a specific platform, repeat the test with the exact dimensions that platform recommends rather than a generic box. The Fit approach produces a file the platform will not distort, while the Stretch approach produces a file that fills the canvas exactly.
What a Local Resize Does Not Do
Comparing approaches is also a chance to recognize what neither Fit nor Stretch will do in a browser-based tool. Resizing does not add detail that is not already in the source, so upscaling a small clip will not turn it into a sharp large clip. Resizing does not remove black bars from a letterboxed source, because the black bars are part of the picture and survive the resize. Resizing does not crop a subject to fill a different ratio, since cropping is a separate operation handled by a tool like the Video Cropper. Resizing does not preserve subtitles, multiple language tracks, or chapter markers, because the WebM output is captured from a canvas rather than remuxed from the source. Resizing does not bypass DRM, and it cannot recover from codecs the browser cannot decode. For frame-accurate delivery, MP4 output, color-managed workflows, or exact bitrate control, a dedicated desktop encoder remains the right choice.
With those limits clear, the comparison question usually reduces to one decision: do you want the source ratio preserved in a bounding box, or do you want the exact dimensions with possible distortion. Fit handles the first case, Stretch handles the second, and the local tool makes it possible to try both on the same source without uploading anything.
For a deeper look, see How Do I Compare Approaches to Extract a Video Frame.