[FFmpeg-devel] [PATCH 1/1] avcodec/dolby_e: Add error recovery when parse_mantissas run out of bits

[Nicolas Gaullier]

Mantissas are the last data in the channel subsegment and it appears it
is sometimes missing a very few bits for the parsing to complete.
This must not be confused with data corruption.
In standard conditions with certified products, it has been observed
that the occurence of this issue is pretty steady and about once every 2
hours. The truncation is at about 950 out of the 1024 values (923 is the
minimum I have seen so far).
The current code raises a severe 'Read past end' error and all data is
lost resulting in 20ms(@25fps) of silence for the affected channel.
This patch introduces a tolerance: if 800 out of the 1024 mantissas have
been parsed, a simple warning is raised and the data is preserved.

Signed-off-by: Nicolas Gaullier <nicolas.gaullier at cji.paris>
---
 libavcodec/dolby_e.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/libavcodec/dolby_e.c b/libavcodec/dolby_e.c
index 9c3f6006c2..1f8442e2e9 100644
--- a/libavcodec/dolby_e.c
+++ b/libavcodec/dolby_e.c
@@ -845,6 +845,7 @@ static int parse_indices(DBEContext *s, DBEChannel *c)
     return 0;
 }
 
+#define MIN_MANTISSAS 800
 static int parse_mantissas(DBEContext *s, DBEChannel *c)
 {
     DBEGroup *g;
@@ -885,6 +886,13 @@ static int parse_mantissas(DBEContext *s, DBEChannel *c)
                     }
                 }
             } else {
+                if (i == c->nb_groups - 1
+                    && count * size1 > get_bits_left(&s->gb)
+                    && get_bits_left(&s->gb) >= 0
+                    && (int)(mnt - c->mantissas) >= MIN_MANTISSAS) {
+                    av_log(s->avctx, AV_LOG_WARNING, "Truncated mantissas @%d, highest frequencies not recoverable\n", (int)(mnt - c->mantissas));
+                    break;
+                }
                 for (k = 0; k < count; k++)
                     mnt[k] = get_sbits(&s->gb, size1) * scale;
             }
-- 
2.30.2