subreader.c: fix excessive memory use with some external subtitles

For each sequence of consecutive partially overlapping subtitles, the
algorithm calculating screen positions for the subtitles allocated a
2*subtitle_count*subtitle_line_count array. With some karaoke
subtitles that had lots of rapidly changing overlapping subtitles this
became large enough to use gigabytes of memory. Make the behavior
saner by limiting the line count to SUB_MAX_TEXT lines (the maximum
number of lines to show on screen at once, currently 12). This
shouldn't change the end result of the algorithm other than possibly
printing different warnings.

1 files changed, 5 insertions, 0 deletions

diff --git a/subreader.c b/subreader.c
index 0776ea2b17..f1b5b44f5e 100644
--- a/subreader.c
+++ b/subreader.c
@@ -1526,6 +1526,11 @@ if ((suboverlap_enabled == 2) ||
 	    }
 	}
 
+        /* Avoid n^2 memory use for the "placeholder" data structure
+         * below with subtitles that have a huge number of
+         * consecutive overlapping lines. */
+        lines_to_add = FFMIN(lines_to_add, SUB_MAX_TEXT);
+
 	// we need a structure to keep trace of the screen lines
 	// used by the subs, a 'placeholder'
 	counter = 2 * sub_to_add + 1;  // the maximum number of subs derived