ffmpeg does not create valid mp4 file

[John Rose]

Running in Terminal:
ffmpeg -r 25 -video_size 1920x1080 -f x11grab -draw_mouse 0 -show_region 1 -i :0.0 -f pulse -ac 2 -i default -vcodec libx265 -y /home/john/Temporary/v.mp4 >/home/john/Temporary/l.txt 2>&1

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ffmpeg 7:3.4.8-0ubuntu0.2
ProcVersionSignature: Ubuntu 4.15.0-112.113-generic 4.15.18
Uname: Linux 4.15.0-112-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.15
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Mon Jul 27 11:32:30 2020
InstallationDate: Installed on 2019-02-12 (530 days ago)
InstallationMedia: Ubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
SourcePackage: ffmpeg
UpgradeStatus: No upgrade log present (probably fresh install)

[John Rose (johnaaronrose)]

Standard Output & Standard Error attached.

[Sebastian Ramacher (s-ramacher)]

Works fine with 4.2.x.