mkv: DATE_RELEASED should behave as TDRL tag in ID3

[malaterre]

Summary of the bug:
How to reproduce:

$ wget 'https://github.com/Matroska-Org/matroska-test-files/raw/8adb681ec6bac497f69757e6ae4935dbf21945b2/test_files/test1.mkv'
$ ffmpeg -i test1.mkv test1.mp4

The output file test1.mp4 should contains an ID3 TDRL tag with value 2010.

Matroska documentation:

• ​https://www.matroska.org/technical/tagging.html#temporal-information

ref:

$ ffmpeg -version
ffmpeg version N-100132-g53b4550bdd Copyright (c) 2000-2020 the FFmpeg developers
built with gcc 8 (Debian 8.3.0-6)
configuration: --prefix=/home/mathieu/ffmpeg_build --pkg-config-flags=--static --extra-cflags=-I/home/mathieu/ffmpeg_build/include --extra-ldflags=-L/home/mathieu/ffmpeg_build/lib --extra-libs='-lpthread -lm' --bindir=/home/mathieu/bin --enable-gpl --enable-gnutls --enable-libaom --enable-libass --enable-libfdk-aac --enable-libfreetype --enable-libmp3lame --enable-libopus --disable-libsvtav1 --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-nonfree
libavutil      56. 61.100 / 56. 61.100
libavcodec     58.114.100 / 58.114.100
libavformat    58. 64.100 / 58. 64.100
libavdevice    58. 11.103 / 58. 11.103
libavfilter     7. 91.100 /  7. 91.100
libswscale      5.  8.100 /  5.  8.100
libswresample   3.  8.100 /  3.  8.100
libpostproc    55.  8.100 / 55.  8.100

[malaterre]

For reference, DATE_RELEASED is the expected tag by kodi/xbmc:

• ​https://github.com/xbmc/xbmc/pull/18892

[malaterre]

Handbrake seems also to expect TDRL (exposed as ffmpeg:date tag) and DATE_RELEASED to be interchangeable:

• ​https://github.com/HandBrake/HandBrake/commit/ab5445d6f279a3477c08f069ff3329b696cb9ac8#diff-3021a0bac4669ab99735e9d5b77671df17c329cb090bd36320d22d562c6e67e3R5454-R5455

[Christoph Päper]

MP3tag also treats them the same as RELEASETIME: ​https://help.mp3tag.de/main_tags.html