Tutorial https://github.com/introlab/rtabmap/wiki/Stereo-mapping#process-a-directory-of-stereo-images-in-ros

stereo_20Hz.launch

<launch>

   <!-- stereo_20Hz directory -->
   <arg name="dir"        default="$(env HOME)/Downloads/stereo_20Hz" />

   <!-- Choose visualization -->
   <arg name="rviz"       default="false" />
   <arg name="rtabmapviz" default="true" />

   <arg name="rate"       default="20" />

   <arg name="ground_is_obstacle" default="false"/>
   <arg name="align_with_ground"  default="false"/>

   <!-- Run stereo_sequence_publisher to publish synchronized images -->
   <node name="stereo_pub" pkg="bag_tools" type="stereo_sequence_publisher.py" output="screen">
      <param name="image_dir_left"         value="$(arg dir)/left"/>
      <param name="image_dir_right"        value="$(arg dir)/right"/>
      <param name="file_pattern"           value="*.jpg"/>
      <param name="camera_info_file_left"  value="$(arg dir)/stereo_20Hz_ros_left.yaml"/>
      <param name="camera_info_file_right" value="$(arg dir)/stereo_20Hz_ros_right.yaml"/>
      <param name="frequency"              value="$(arg rate)"/>
      <remap from="/stereo_camera/left/image_color"  to="/stereo_camera/left/image_raw" />
      <remap from="/stereo_camera/right/image_color" to="/stereo_camera/right/image_raw" />
      <remap from="/stereo_camera/left/camera_info"  to="/stereo_camera/left/camera_info" />
      <remap from="/stereo_camera/right/camera_info" to="/stereo_camera/right/camera_info" />
   </node>

   <!-- Run the ROS package stereo_image_proc for image rectification -->
   <group ns="/stereo_camera" >
      <node pkg="stereo_image_proc" type="stereo_image_proc" name="stereo_image_proc"/>
   </group>

   <!-- rotate camera so z axis is up and x forward. -->
   <arg name="pi/2" value="1.5707963267948966" />
   <node pkg="tf" type="static_transform_publisher" name="camera_base_link" args="0 0 0 -$(arg pi/2) 0 -$(arg pi/2) camera_link stereo_20Hz_left 100" /> 

   <include file="$(find rtabmap_ros)/launch/rtabmap.launch">
      <arg name="rtabmap_args" value="--delete_db_on_start --Vis/EstimationType 1 --Vis/MinInliers 15 --SURF/HessianThreshold 100 --Grid/3DGroundIsObstacle $(arg ground_is_obstacle) --Odom/AlignWithGround $(arg align_with_ground)" />
      <arg name="stereo"           value="true" />
      <arg name="rviz"             value="$(arg rviz)" />
      <arg name="rtabmapviz"       value="$(arg rtabmapviz)" />
   </include>

</launch>