Tvheadend

The following format string prevent recording because the filename generated is too long :
$t $-c - %F+%R $-e$.s$n.$x

Is it possible to truncate the filename within the limits of the filesystem (ext4, ~255 chars) ?

Log :
Aug 9 16:34:30 nas tvheadend²²²⁴¹: dvr: "Des trains pas comme les autres" on "France 5" recorder starting
Aug 9 16:34:30 nas tvheadend²²²⁴¹: mpegts: 506MHz in TNT COFDM BB - tuning on DiBcom 7000PC : DVB-T #0 - T5 bout
Aug 9 16:34:30 nas tvheadend²²²⁴¹: subscription: 0019: "DVR: Des trains pas comme les autres" subscribing on channel "France 5", weight: 300, adapter: "DiBcom 7000PC : DVB-T #0 - T5 bout", network: "TNT COFDM BB", mux: "506MHz", provider: "GR1", service: "France 5", profile="matroska"
Aug 9 16:34:32 nas tvheadend²²²⁴¹: mkv: (null): Unable to create file, open failed -- Nom de fichier trop long
Aug 9 16:34:32 nas tvheadend²²²⁴¹: dvr: Recording error: "/mnt/STORAGE/Enregistrements/Des trains pas comme les autres -France 5 - 2015-08-09+16-36 .Norvege. Documentaire. 2015. Saison 5. Philippe Gougler parcourt la Norvege, en plein hiver ; entre autres curiosites typiques du pays, il visite un train chasse-neige et contemple une aurore boreale..mkv": Unable to open file
Aug 9 16:34:32 nas tvheadend²²²⁴¹: subscription: 0019: "DVR: Des trains pas comme les autres" unsubscribing from "France 5"
Aug 9 16:34:32 nas tvheadend²²²⁴¹: dvr: "Des trains pas comme les autres" on "France 5": End of program: File Not Created

And when deleting the recording :
Aug 9 18:32:02 nas tvheadend²²²⁴¹: dvr: Unable to remove file '/mnt/STORAGE/Enregistrements/Des trains pas comme les autres -France 5 - 2015-08-09+16-36 .Norvege. Documentaire. 2015. Saison 5. Philippe Gougler parcourt la Norvege, en plein hiver ; entre autres curiosites typiques du pays, il visite un train chasse-neige et contemple une aurore boreale..mkv' from disk - - Erreur inconnue -36

Looking at that log, it seems that the EPG source included the description in the subtitle.