[FFmpeg-devel] Add Lame tag to the Xing/Info header of mp3 files - Fixes ticket #3577

[Giovanni Motta]

Fixes ticket #3577

A few notes/comments:

- A failing FATE test has been updated with new CRC.

- The Lame info tag is generated by libmp3lame and passed to the mp3enc via extradata.

- To keep the size of the tag constant and simplify the code, vbr_scale is always added.

- The Lame string vendor in the tag is fixed length, so vendor is trimmed
  to 9 bytes and padded with 0x20 if shorter.

- replay_gain and find_peak need a version of lame patched with
  libmp3lame/lame.c Revision 1.367 (patch tracker item #66): http://sourceforge.net/p/lame/patches/66/
  They have no effect otherwise.

- find_peak_sample only works if Lame is configured with --enable-decoder.
  It has no effect otherwise.

- Some fields in the Lame tag are not set because not accessible from
  the set/get API (preset and noise shaping, for example). I will bring this to
  the attention of the Lame developers and help there with any change if we
  decide to merge the patch.

Thanks

Giovanni