Proposed fix for the Linux (maybe other OSs) issue, because of depre…

[ebachard]

…cated CONSTANTS

Hello,

I had to fix some issues on Linux (x86_64, Mint 18.3) to make it compile.

Just in case you fond it usefull, take the license you need, and thanks a lot for sharing your code :-)

[powderluv]

Verified this patch works to build Pangolin on 10.13.5 and ffmpeg 4 from homebrew

[NikolausDemmel]

I can also confirm that this patch fixes compilation also for Pangolin master with ffmpeg 4 on macOS Sierra.

[TaylorDixonHD]

Confirmed that this fix works for macOS HighSierra 10.13.5

[stevenlovegrove]

Finally got around to testing this on my machine and cherry-picked as d9daba6
Thanks!

[ra0e]

I still can't build it. Still getting same errors on Ubuntu 20.04 even though this patch is in master.

 error: ‘CODEC_FLAG_GLOBAL_HEADER’ was not declared in this scope; did you mean ‘AV_CODEC_FLAG_GLOBAL_HEADER’?
  519 |         stream->codec->flags |= CODEC_FLAG_GLOBAL_HEADER;

[marcojob]

I still can't build it. Still getting same errors on Ubuntu 20.04 even though this patch is in master.

 error: ‘CODEC_FLAG_GLOBAL_HEADER’ was not declared in this scope; did you mean ‘AV_CODEC_FLAG_GLOBAL_HEADER’?
  519 |         stream->codec->flags |= CODEC_FLAG_GLOBAL_HEADER;

Same here, also on Ubuntu 20.04