[mythtv] Decision on FFmpeg repository

[Peter Bennett]

I would like to get a decision on what to do about a couple of FFmpeg 
questions:

1. Use FFmpeg master or release branch? My recommendation is to use master.
- the FFmpeg website recommends using master for those who are compiling 
FFmpeg themselves. It states that the release branches are for those who 
rely on downloaded prebuilt packages 
(https://ffmpeg.org/download.html#repositories).
- Only master has the recent mediacodec changes which I need for android.
- If we sync to master, we can use a better approach for the repository 
(question 2 below).

2. What method should we use for storing and syncing with FFmpeg source?
Options are:
a. Reapply patches to the source from FFmpeg, resolve conflicts, and 
copy the source over what we have in MythTV (current process). This can 
be very time-consuming.

b. Use a subtree in the MythTV repository.
- This will not work if we use a release branch (question 1).
- When resyncing, we can do a git merge of the subtree from FFmpeg.
- We can cherry-pick changes needed without resyncing everything.
- We can sync to any required commit, we don't need to go all the way to 
the latest commit.
- git log shows FFmpeg commits intermingled with MythTV. You can use 
"git log -- mythtv" which eliminates those.
- This imports some 90,000 extra commits from FFmpeg.

You can see an example of the subtree in use at 
https://github.com/bennettpeter/mythtv/tree/ffmpeg-subtree or clone that 
repo and look at the ffmpeg-subtree branch.

c. Keep our own customized FFmpeg repository with patches applied.
- This will not work if we use a release branch (question 1).
- When resyncing, do a git pull or merge on the private FFmpeg 
repository. Then copy the entire source over the MythTV FFmpeg source.
- We can cherry-pick changes needed without resyncing everything.
- We can sync to any required commit, we don't need to go all the way to 
the latest commit.
- git log in MythTV does not show all the FFmpeg commits.
- git log in the private FFmpeg repository shows records of our patches 
along with all the FFmpeg commits.
- We can perform periodic pulls into the private FFmpeg repository 
without affecting MythTV. This will make the eventual copying into 
MythTV quicker and easier.
- Any FFmpeg patches that we apply between copying into MythTV must be 
applied in both MythTV and FFmpeg repositories, or apply them in the 
private FFmpeg repository and then wait for the next copy into MythTV.

You can see an example of FFmpeg with patches applied at 
https://github.com/bennettpeter/FFmpeg

Peter