Usually tiles recalculated when new image comes in, however when 'overlap' option is in effect - tiles recalculated multiple times.
And when layout also has 'zoom' option - when image recalculated it each round zooms itself deeper and deeper, until new images comes and image resets to proper state.
This looks like flicker.

The fix is to always take for zoom calculations real image dimensions instead of previously recalculated.

HOWEVER!
There are too many math and corner cases in mod_conference, so i propose it to be reviewed by widest audience of people who wrote mod_conference!

+ don't shoot in a leg and keep 'rtt_now' value correct (even if we clear it few lines after), because after some time it could be changed.

FS-11362 Rearrange poll() errors handling to properly report poll hangup. Handle and log case when client sent close request. Add errno to errors where applicable.

FS-11362 FS could close client verto connection due to incorrect handling of SSL function return values (when SSL layer need to communicate with client on its own, f.e. keys re-negotiation)

FS-11360 Fix FS degradation over time in DTLS layer (especially if outdoing packets rate higher that incoming)

When we handle DTLS layer in do_dtls() and there are no incoming packets yet - we still call BIO_write() with NULL buffer and it is an error and BIO_write() will stuck for a long time in libssl/libcrypto error subsystem.
(that also possibly relates to fact that libssl/libcrypto init/deinit/error-handling is broken in general in FS, however that is another big issue)

Merge pull request #1580 in FS/freeswitch from ~ANDYWOLK/freeswitch:bugfix/FS-11368-use-system-flite1 to master

* commit 'ccc23b78':
  FS-11368: [mod_flite] Use system flite1 instead of libflite

Merge pull request #1577 in FS/freeswitch from ~ANDYWOLK/freeswitch:FS-11361-switch-debian-packages-building to master

* commit 'f98da7d5':
  FS-11361: [Build-System] Switch Debian packages building script util.sh from jessie stable to stretch stable.

Merge pull request #1579 in FS/freeswitch from ~ANDYWOLK/freeswitch:feature/FS-11368-use-system-libflite to master

* commit 'bcd355fe':
  FS-11368: [mod_flite] Use system libflite.

FS-11361: [Build-System] Switch Debian packages building script util.sh from jessie stable to stretch stable.

Merge pull request #1553 in FS/freeswitch from ~THEHUNMONKGROUP/freeswitch:feature/FS-11287-provide-option-for-user-managed to master

* commit '96af587b':
  FS-11287: Provide option for user managed streams in Verto

Merge pull request #1548 in FS/freeswitch from ~THEHUNMONKGROUP/freeswitch:bugfix/FS-11284-fix-legacy-broken-video-constraints to master

* commit '31641749':
  FS-11284: Fix legacy/broken video constraints for specifying a video deviceId

Merge pull request #1544 in FS/freeswitch from ~THEHUNMONKGROUP/freeswitch:bugfix/FS-11280-allow-overriding-permissioncallback to master

* commit '36d9f7bc':
  FS-11280: Allow overriding permissionCallback per Verto dialog

Merge pull request #1522 in FS/freeswitch from ~THEHUNMONKGROUP/freeswitch:bugfix/FS-11149-playing-video-files-assigned-a-res_id to master

* commit '1fc08365':
  FS-11149: Playing video files assigned a res_id not correctly updated on layout change

* commit 'be782776':
  FS-11189 add back default flags LOOP_FILTER and PSNR for H264
  FS-11189 set default cpu string to cpu/2/4 if not configured
  FS-11189 add helper functions and macros to dump encoder context params
  FS-11189 add default av conf to vanilla
  FS-11189 use AV_INPUT_BUFFER_PADDING_SIZE instead of FF_INPUT_BUFFER_PADDING_SIZE in newer ffmpeg

Merge pull request #1552 in FS/freeswitch from ~THEHUNMONKGROUP/freeswitch:feature/FS-11286-add-onremotestream-callback-to-verto to master

* commit '61cdf636':
  FS-11286: Add onRemoteStream callback to Verto dialogs

Merge pull request #1546 in FS/freeswitch from ~THEHUNMONKGROUP/freeswitch:bugfix/FS-11282-remove-ios-controls-hack-not-needed to master

* commit '5038ca76':
  FS-11282: Remove iOS 'controls' hack, not needed

Merge pull request #1545 in FS/freeswitch from ~THEHUNMONKGROUP/freeswitch:bugfix/FS-11281-verto.newcall-dialog-callback-overrides to master

* commit '5f96f669':
  FS-11281: Verto.newCall dialog callback overrides should be set before invite

* commit '82350ace':
  FS-11164 fix unused function regression from 578d914b

Merge pull request #1572 in FS/freeswitch from bugfix/FS-11276-regression-dedicated-video-layers to master

* commit 'ecdae105':
  FS-11279: Wrap verto.clientReady message callback in check for onMessage callback function

The verto.clientReady event calls the onMessage callback function passed in
the Verto object. We should check for the existence of this callback function
before trying to call it.

Merge pull request #1549 in FS/freeswitch from ~THEHUNMONKGROUP/freeswitch:bugfix/FS-11285-overconstrainederror-on-some-android to master

* commit 'ef647e3e':
  FS-11285: OverconstrainedError on some Android front cameras when frameRate.min is specified

Merge pull request #1547 in FS/freeswitch from ~THEHUNMONKGROUP/freeswitch:bugfix/FS-11283-ios-doesn-t-support-beforeunload to master

* commit '954b2564':
  FS-11283: iOS doesn't support beforeunload, use recommended pagehide for that platform

Merge pull request #884 in FS/freeswitch from ~THEHUNMONKGROUP/freeswitch:bugfix/FS-9258-recursive-calls-to-speedtest to master

* commit 'c037fc8c':
  FS-9258: Recursive calls to $.verto.rpcClient.speedTest() don't work

Merge pull request #1541 in FS/freeswitch from ~THEHUNMONKGROUP/freeswitch:bugfix/FS-11276-regression-dedicated-video-layers to master

* commit 'c83f7871':
  FS-11276: dedicated video layers can no longer become audio floor holder

SWITCH_DECLARE(switch_status_t) switch_dial_handle_create(switch_dial_handle_t **handle);
SWITCH_DECLARE(void) switch_dial_handle_destroy(switch_dial_handle_t **handle);
SWITCH_DECLARE(void) switch_dial_handle_add_leg_list(switch_dial_handle_t *handle, switch_dial_leg_list_t **leg_listP);
SWITCH_DECLARE(void) switch_dial_leg_list_add_leg(switch_dial_leg_list_t *parent, const char *dial_string, switch_dial_leg_t **legP);
SWITCH_DECLARE(void) switch_dial_handle_add_global_var(switch_dial_handle_t *handle, const char *var, const char *val);
SWITCH_DECLARE(void) switch_dial_handle_add_global_var_printf(switch_dial_handle_t *handle, const char *var, const char *fmt, ...);
SWITCH_DECLARE(switch_status_t) switch_dial_handle_add_leg_var(switch_dial_leg_t *leg, const char *var, const char *val);
SWITCH_DECLARE(switch_status_t) switch_dial_handle_add_leg_var_printf(switch_dial_leg_t *leg, const char *var, const char *fmt, ...);
SWITCH_DECLARE(int) switch_dial_handle_get_peers(switch_dial_handle_t *handle, int idx, char **array, int max);
SWITCH_DECLARE(int) switch_dial_handle_get_vars(switch_dial_handle_t *handle, int idx, switch_event_t **array, int max);
SWITCH_DECLARE(switch_event_t *) switch_dial_handle_get_global_vars(switch_dial_handle_t *handle);
SWITCH_DECLARE(switch_event_t *) switch_dial_leg_get_vars(switch_dial_leg_t *leg);
SWITCH_DECLARE(int) switch_dial_handle_get_total(switch_dial_handle_t *handle);
SWITCH_DECLARE(void) switch_ivr_orig_and_bridge(switch_core_session_t *session, const char *data, switch_dial_handle_t *dh);

add switch_dial_handle_t *dh to end of args for switch_ivr_originate