How do I resize video ffmpeg?
Scales to a target width while computing a height that stays even, which H.264 requires.
Resize a video with FFmpeg
Scales to a target width while computing a height that stays even, which H.264 requires.
ffmpeg -i https://cdn.rendobar.com/assets/examples/sample.mp4 -vf scale=640:-2 -c:v libx264 -crf 23 -t 5 out.mp4- Encode
- 481 ms
- Output
- 269.0 KB
- Cost
- $0.0020
- Result
- 640x360
job_ece789351fe7440d
The part everyone gets wrong
Use -2, never -1. Both preserve the aspect ratio, but -2 rounds to an even number and -1 does not. H.264 with yuv420p needs both dimensions even, so -1 produces an encoder failure on roughly half of all source aspect ratios.
What the common version does
An odd width with -1 can compute an odd height, and libx264 refuses to encode odd dimensions.
ffmpeg -i https://cdn.rendobar.com/assets/examples/sample.mp4 -vf scale=641:-1 -c:v libx264 -crf 23 -t 5 out.mp4It errors
This one fails outright, which is the good case. You find out immediately.
job_ec395f0805e245a6
Frequently asked questions
What goes wrong most often?
Use -2, never -1. Both preserve the aspect ratio, but -2 rounds to an even number and -1 does not. H.264 with yuv420p needs both dimensions even, so -1 produces an encoder failure on roughly half of all source aspect ratios.
What happens if I get it wrong?
We ran the naive version too. This one fails outright, which is the good case. You find out immediately.
Do I need FFmpeg installed?
Not with Rendobar. The command on this page ran through the API against a URL, with no local FFmpeg and no server. The job id below it is the job that produced these numbers.
More recipes, all measured
Trim a video without re-encoding Cuts a section out of a video by copying streams, which is effectively instant and lossless. Remove audio from a video Strips the audio track and copies the video untouched, so there is no quality loss and almost no work. Rotate a video with FFmpeg Rotates the picture in 90-degree steps and clears the rotation metadata so players do not rotate it again. Speed up or slow down a video Changes video and audio speed together, which needs two filters because one alone desynchronises the file.
Run this without installing FFmpeg
This exact command ran through the API against a URL.