Add docs and Changelog entry for the -copytb option added in r26340.

Originally committed as revision 26362 to svn://svn.ffmpeg.org/ffmpeg/trunk

Changelog

@@ -72,6 +72,7 @@ version <next>:
 - SubRip (srt) subtitle decoder
 - floating-point AC-3 encoder added
 - Lagarith decoder
+- ffmpeg -copytb option added
 
 
 version 0.6:

doc/ffmpeg.texi

@@ -687,6 +687,8 @@ the parameter is the maximum samples per second by which the audio is changed.
 without any later correction.
 @item -copyts
 Copy timestamps from input to output.
+@item -copytb
+Copy input stream time base from input to output when stream copying.
 @item -shortest
 Finish encoding when the shortest input stream ends.
 @item -dts_delta_threshold