Some information on hooks that are available in Media Mover:

Files

hook_media_mover_file_load: Allows modules to modify a Media Mover file when it is being loaded. This is called after the file is pulled from the database and any of the steps which created it have had the option to add data to it. Note that under Drupal 7 this will likely be part of hook_file_load(). This is called after the file is loaded from cache (if requested). You can test if a file is loaded from cache with $file->cached == TRUE
hook_media_mover_file_save: Allows modules to modify a Media Mover file before it is saved. This data will be stored in $file->data.
hook_media_mover_file_process_pre(&$file, $step): Called just before a file is processed
hook_media_mover_file_process_post(&$file, $step): Called just after a file has been processed

Steps

hook_media_mover_step_load(&$step)
hook_media_mover_step_save(&$step)

Configurations

hook_media_mover_configuration_load(&$configuration)
hook_media_mover_configuration_save(&$configuration)

Other

hook_media_mover_process_control(&$file, $step, &$errors): Allows modules to block a run from happening based on things like number of files processed, cpu load, etc. If $errors is populated, the file will not be processed. $errors will be logged to watchdog. Called from $step->run($file)