You know what... I'm apparently lying to you... I swear that you used to be able to download .deb files from Builds, but I can't find a link now. My apologies.
In which case you're back togit checkout <specific-version-hash>, and then you can useAutobuild.sh to build the .deb file, and then usesudo dpkg -i <file> to install it. The instructions for building are in the link below, you'd just use that <specific-version-hash> to get an historical version from master instead of the latest code.
https://tvheadend.org/projects/tvheadend/wiki/Building
So, aftergit clone, you can thencd tvheadend andgit checkout <specific-version-hash>.
Of course, if you want to use a
much earlier version, or a version from a different branch, then things are different. 3.4 is available in the stable repository, so just follow those instructions - otherwise, you're going to have to read up on git branches to check out something other than master.