Mark, if you are referring to the mpmc repo, I changed it and this is what I got.
deb
http://mirrordirector.raspbian.org/raspbian/ stretch main contrib non-free $
# Uncomment line below then 'apt-get update' to enable 'apt-get source'
#deb-src http://archive.raspbian.org/raspbian/ stretch main contrib non-free rpi
#deb
https://dl.bintray.com/djbenson/deb wheezy stable (for stable branch)
#deb https://dl.bintray.com/djbenson/deb wheezy unstable (for unstable branch)
#deb
https://dl.bintray.com/tvheadend/ubuntu master main
#deb https://dl.bintray.com/tvheadend/ubuntu unstable main
#deb https://dl.bintray.com/tvheadend/deb/dists/ wheezy release
deb
https://dl.bintray.com/mpmc/deb rasbianstretch stable
#deb http://apt.tvheadend.org/stable wheezy main
pi@rasbian-kodi:~ $ sudo apt-get update
Ign:1
https://dl.bintray.com/mpmc/deb rasbianstretch InRelease
Ign:2
https://dl.bintray.com/mpmc/deb rasbianstretch Release
Ign:3
https://dl.bintray.com/mpmc/deb rasbianstretch/stable all Packages
Ign:4
https://dl.bintray.com/mpmc/deb rasbianstretch/stable armhf Packages
Ign:5
https://dl.bintray.com/mpmc/deb rasbianstretch/stable Translation-en
Ign:3
https://dl.bintray.com/mpmc/deb rasbianstretch/stable all Packages
Ign:4
https://dl.bintray.com/mpmc/deb rasbianstretch/stable armhf Packages
Ign:5
https://dl.bintray.com/mpmc/deb rasbianstretch/stable Translation-en
Ign:3
https://dl.bintray.com/mpmc/deb rasbianstretch/stable all Packages
Ign:4
https://dl.bintray.com/mpmc/deb rasbianstretch/stable armhf Packages
Ign:5
https://dl.bintray.com/mpmc/deb rasbianstretch/stable Translation-en
Ign:3
https://dl.bintray.com/mpmc/deb rasbianstretch/stable all Packages
Ign:4
https://dl.bintray.com/mpmc/deb rasbianstretch/stable armhf Packages
Ign:5
https://dl.bintray.com/mpmc/deb rasbianstretch/stable Translation-en
Ign:3
https://dl.bintray.com/mpmc/deb rasbianstretch/stable all Packages
Ign:4
https://dl.bintray.com/mpmc/deb rasbianstretch/stable armhf Packages
Ign:5
https://dl.bintray.com/mpmc/deb rasbianstretch/stable Translation-en
Ign:3
https://dl.bintray.com/mpmc/deb rasbianstretch/stable all Packages
Err:4
https://dl.bintray.com/mpmc/deb rasbianstretch/stable armhf Packages
404 Not Found
Ign:5
https://dl.bintray.com/mpmc/deb rasbianstretch/stable Translation-en
Get:6
http://archive.raspberrypi.org/debian stretch InRelease [25.3 kB]
Get:7
http://mirrordirector.raspbian.org/raspbian stretch InRelease [15.0 kB]
Get:8
http://archive.raspberrypi.org/debian stretch/main armhf Packages [144 kB]
Get:9
http://mirrordirector.raspbian.org/raspbian stretch/main armhf Packages [11.7 MB]
Fetched 11.8 MB in 1min 22s (144 kB/s)
Reading package lists... Done
W: The repository '
https://dl.bintray.com/mpmc/deb rasbianstretch Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: Failed to fetch
https://dl.bintray.com/mpmc/deb/dists/rasbianstretch/stable/binary-armhf/Packages 404 Not Found
E: Some index files failed to download. They have been ignored, or old ones used instead.
pi@rasbian-kodi:~ $ sudo apt-get install tvheadend
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package tvheadend is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package 'tvheadend' has no installation candidate
pi@rasbian-kodi:~ $