bytedeco/javacv

Scalling down with FFmpegFrameGrabber produces low quality results

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#1,279 opened on Aug 22, 2019

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Description

This is something I noticed. I'm not actually sure if this is something you can fix on your end, I just want to make sure my setup is OK.

So, I decode frames from a video. Video resolution is 1920x1080, I need 1280x720.

Now, I can scale it down with FFmpegFrameGrabber, like so:

            grabber.setImageWidth(1280);
            grabber.setImageHeight(720);
            grabber.setPixelFormat(PIXEL_FORMAT);
            grabber.setImageScalingFlags(SWS_BICUBIC);

or I can decode at video's resolution and scale it down with OpenCV.

The thing is get better results with the OpenCV method, so I wanted to make sure if there's anything I could do to up the quality when using FFmpegFrameGrabber alone? I tried different image scaling flags, they don't seem to make much of a difference (if any at all).

Contributor guide

Research direction
Investigate the scaling algorithm used by FFmpegFrameGrabber and compare with OpenCV's scaling. Look into the sws flags and possible color conversion issues.
Tech stack
java
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Java
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
75