I have been looking for a way to make the ADV7513 or similar part output a mono audio signal over HDMI, even though the input audio supplied via I2S is stereo. For various reasons it is not trivial for us to make the input mono in the first place.
From the programmer's manual section 4.4.3 I have:
"The I2S can be routed to different subpackets using registers 0xE – 0x11."
..and then Table 69 specifies these registers. It looks from the table like it might be possible to specify the source of both subpacket 0, right channel and subpacket 0, left channel to be I2S0 left channel and so create a mono signal. ie. set register 0xE [5:3] = 0 and [2:0] = 0.
Will this work?