[mythtv] Harmonizing mpegts-mythtv.(c|h) with FFmpeg's mpegts.(c|h)

[Scott Theisen]

Peter,

My harmonization of mpegts-mythtv.* is almost complete.  (This is on top 
of my rebase/4.4m3 branch, but should have no issues being applied on 
top of mythtv/FFmpeg/master.)

See https://github.com/ulmus-scott/FFmpeg/commits/harmonize for the 
original commit order and 
https://github.com/ulmus-scott/FFmpeg/commits/harmonize2 for reordered 
with problematic commits moved to the end.

I have been testing with some of my local stations and the samples from 
https://code.mythtv.org/trac/ticket/13557 / 
https://github.com/MythTV/mythtv/issues/351 and everything is fine 
through mpegts-mythtv.c: harmonize ff_parse_mpeg2_descriptor() part 1 
<https://github.com/ulmus-scott/FFmpeg/commit/c22901ac83f9955f3846d33f79f4ddb8a07aeb8d>.

I have been banging my head against the brick wall that is pat_cb() and 
pmt_cb().  (It started out fairly straightforward, but dealing with 
those two functions and the 17 year old changes buried under updates has 
been increasingly frustrating.)

mpegts-mythtv.c: pmt_cb(): harmonize part 6 
<https://github.com/ulmus-scott/FFmpeg/commit/58cc290d552169f2388e83384e1a28a22a710ae7> 
appears to actually work fine; however, the logic for calling the 
streams_changed() callback is wrong, so it isn't called when it was 
previously. Correcting it 
<https://github.com/ulmus-scott/FFmpeg/commit/8a8dc3d5599bd61368c26ed410248cad20f7fa25>, 
sort of (it updates on every different PMT, instead of if the streams 
actually changed), causes a segmentation fault in 
https://github.com/MythTV/mythtv/blob/709d05c0d6928e927ea1b0cc2b2c46bc80d40055/mythtv/libs/libmythtv/decoders/avformatdecoder.cpp#L2652 
.

I suspect that is because the PSIPTable does not create a copy of its 
input data, which is then freed while the PMT table is being accessed.

mpegts-mythtv.c: pat_cb() harmonization part 3 
<https://github.com/ulmus-scott/FFmpeg/commit/6887b3127bcc2b8211e0fd7ab9828965ffe847f0> 
causes a different segmentation fault in FFmpeg (dump.c trying to read 
the st->metadata AVDictionary for the "language").  I wouldn't worry 
about this one right now since I feel pmt_cb() has a higher priority, so 
ff_parse_mpeg2_descriptor() can be minimally modified.


Let me know if you want me to open another set of pull requests with the 
"good" commits for easier testing.

Any thoughts on how to complete the harmonization would also be appreciated.

Regards,

Scott
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