In order to be able to play H.264/AVC lossless encoded videos with the Adobe Flash plug-in, some non-standard-confrom modifications must be made to the used H.264/AVC encoder.
The necessary modifcations for x264 (core: 125 r2200M 999b753) are as following:
In common\set.h, line 37 modify the profil_idv by replacing
PROFILE_HIGH444_PREDICTIVE = 244
PROFILE_HIGH444_PREDICTIVE = 144
The resulting definition should then look like this:
In encoder\macroblock.c, line 488 and following, the functions
must be modified by removing the if blocks, which are checking for vertical and horizontal prediction.
The resulting functions should then look like this: