mplayer scales some videos incorrectly

[Dave Macfarlane]

Videos with frames 720x576, pixel aspect ratio 64:45, should display with aspect 16:9.
Instead, this version of mplayer displays a window of size 1024x576, as expected, but content displayed in it appears to have been scaled in size by 64:45 in BOTH x and y dimensions, so shape is wrong, and is too big vertically for the window.

After some experimentation - different container formats, different encoders, different frame sizes, different pixel aspects, I only see problem with pixel aspect 64:45.

Videos like this display OK in VLC, and in mplayer v.1.2.1 (Lubuntu 18.04).

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: mplayer 2:1.3.0-8build5
ProcVersionSignature: Ubuntu 5.4.0-25.29-generic 5.4.30
Uname: Linux 5.4.0-25-generic x86_64
ApportVersion: 2.20.11-0ubuntu27
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: LXQt
Date: Mon Apr 20 20:46:48 2020
InstallationDate: Installed on 2020-04-14 (6 days ago)
InstallationMedia: Lubuntu 20.04 LTS "Focal Fossa" - Beta amd64 (20200413)
SourcePackage: mplayer
UpgradeStatus: No upgrade log present (probably fresh install)