Logging can be turned off:
RTMP access logger supports formatting with a number of predefined variables. The complete list of supported variables can be found on directives page in log_format directive description.
log_format new '$remote_addr $bytes_sent';
access_log logs/rtmp_access.log new;
Default format combined is supported as well. Here's the definition of this format:
$remote_addr [$time_local] $command "$app" "$name" "$args" -
$bytes_received $bytes_sent "$pageurl" "$flashver" ($session_readable_time)