Fixes #6500
I checked the h263 specification and the current implementation is already
quite thorough. False positives, like #6500, can happen by pure chance. To
improve the situation it would be necessary to further parse and validate
additional data from the h263 "picture" layer.
A possible alternative is to add some heuristic in relation with TR (time
reference): in all h263 samples which I could find, the first TR is zero and
successive ones differ from the previous (mod 0xFF) by a small value, typically
1. The score could be lowered if this doesn't happen (e.g. the value is 214 in
#6500).
For now, my proposal is something much simpler, which takes care of #6500 and
possibly other "unlucky" cases: the score is reduced to 12 if only a single
valid PSC is found. Note that the current implementation already
unconditionally reduces the score to 25 if there are less than 4 valid PSCs.
Signed-off-by: Dario Andreani <darioan...@gmail.com>
---
libavformat/h263dec.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/libavformat/h263dec.c b/libavformat/h263dec.c
index 0736158bfe..ff2828ed83 100644
--- a/libavformat/h263dec.c
+++ b/libavformat/h263dec.c
@@ -71,7 +71,7 @@ static int h263_probe(const AVProbeData *p)
if(valid_psc > 2*invalid_psc + 2*res_change + 3){
return AVPROBE_SCORE_EXTENSION;
}else if(valid_psc > 2*invalid_psc)
- return AVPROBE_SCORE_EXTENSION / 2;
+ return valid_psc > 1 ? AVPROBE_SCORE_EXTENSION / 2 :
AVPROBE_SCORE_EXTENSION / 4;
return 0;
}
--
2.28.0
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