Lost beginning left brackets in .lrc when convert to .srt

[agguser]

Summary of the bug:

Left brackets at the beginning of lines in .lrc lyrics file is lost when convert to .srt

How to reproduce:

% echo '[00:00.00][abc]def[ghi]' | ffmpeg -i - -f srt -
ffmpeg version 4.0 Copyright (c) 2000-2018 the FFmpeg developers
  built with gcc 8.1.0 (GCC)
  configuration: --prefix=/usr --disable-debug --disable-static --disable-stripping --enable-avresample --enable-fontconfig --enable-gmp --enable-gnutls --enable-gpl --enable-ladspa --enable-libass --enable-libbluray --enable-libdrm --enable-libfreetype --enable-libfribidi --enable-libgsm --enable-libiec61883 --enable-libmodplug --enable-libmp3lame --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libv4l2 --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxcb --enable-libxml2 --enable-libxvid --enable-nvenc --enable-omx --enable-shared --enable-version3
  libavutil      56. 14.100 / 56. 14.100
  libavcodec     58. 18.100 / 58. 18.100
  libavformat    58. 12.100 / 58. 12.100
  libavdevice    58.  3.100 / 58.  3.100
  libavfilter     7. 16.100 /  7. 16.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  1.100 /  5.  1.100
  libswresample   3.  1.100 /  3.  1.100
  libpostproc    55.  1.100 / 55.  1.100
Input #0, lrc, from 'pipe:':
  Duration: N/A, bitrate: N/A
    Stream #0:0: Subtitle: text
Output #0, srt, to 'pipe:':
  Metadata:
    encoder         : Lavf58.12.100
    Stream #0:0: Subtitle: subrip (srt)
    Metadata:
      encoder         : Lavc58.18.100 srt
Stream mapping:
  Stream #0:0 -> #0:0 (text (native) -> subrip (srt))
1
00:00:00,000 --> 1193:02:47,295
abc]def[ghi]

size=       0kB time=00:00:00.00 bitrate=N/A speed=   0x
video:0kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 300.000000%

[Carl Eugen Hoyos]

For future tickets: Please remember that only current FFmpeg git head is supported on this bug tracker.