demux: mp4: report current trun sample pos in debug

modules/demux/mp4/mp4.c

@@ -4570,7 +4570,7 @@ static int FragDemuxTrack( demux_t *p_demux, mp4_track_t *p_track,
         msg_Dbg( p_demux, "tk(%i)=%"PRId64" mv=%"PRId64" pos=%"PRIu64, p_track->i_track_ID,
                  VLC_TICK_0 + MP4_rescale_mtime( i_dts, p_track->i_timescale ),
                  VLC_TICK_0 + MP4_rescale_mtime( i_pts, p_track->i_timescale ),
-                 p_track->context.i_trun_sample_pos );
+                 p_track->context.i_trun_sample_pos - i_read );
 #endif
         if ( p_track->p_es )
         {