[FFmpeg-cvslog] avcodec/h264_parser: Reduce needed history for parsing mb index

[Michael Niedermayer]

ffmpeg | branch: release/3.4 | Michael Niedermayer <michael at niedermayer.cc> | Fri Jun 22 21:45:59 2018 +0200| [0fce2872e43d511284293b77089145409864475a] | committer: Michael Niedermayer

avcodec/h264_parser: Reduce needed history for parsing mb index

This fixes a bug/regression with very small packets
Fixes: output_file

Regression since: 0782fb6bcb32fe3ab956a99af4cc472ff81da0c2

Reported-by: Thierry Foucu <tfoucu at google.com>
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
(cherry picked from commit d25c945247979a88fac6bb3b7a26370262b96ef1)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=0fce2872e43d511284293b77089145409864475a
---

 libavcodec/h264_parser.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/libavcodec/h264_parser.c b/libavcodec/h264_parser.c
index dd0a965af0..84988e6d79 100644
--- a/libavcodec/h264_parser.c
+++ b/libavcodec/h264_parser.c
@@ -121,20 +121,23 @@ static int h264_find_frame_end(H264ParseContext *p, const uint8_t *buf,
             }
             state = 7;
         } else {
+            unsigned int mb, last_mb = p->parse_last_mb;
+            GetBitContext gb;
             p->parse_history[p->parse_history_count++] = buf[i];
-            if (p->parse_history_count > 5) {
-                unsigned int mb, last_mb = p->parse_last_mb;
-                GetBitContext gb;
 
-                init_get_bits(&gb, p->parse_history, 8*p->parse_history_count);
-                p->parse_history_count = 0;
-                mb= get_ue_golomb_long(&gb);
+            init_get_bits(&gb, p->parse_history, 8*p->parse_history_count);
+            mb= get_ue_golomb_long(&gb);
+            if (get_bits_left(&gb) > 0 || p->parse_history_count > 5) {
                 p->parse_last_mb = mb;
                 if (pc->frame_start_found) {
-                    if (mb <= last_mb)
+                    if (mb <= last_mb) {
+                        i -= p->parse_history_count - 1;
+                        p->parse_history_count = 0;
                         goto found;
+                    }
                 } else
                     pc->frame_start_found = 1;
+                p->parse_history_count = 0;
                 state = 7;
             }
         }
@@ -149,7 +152,7 @@ found:
     pc->frame_start_found = 0;
     if (p->is_avc)
         return next_avc;
-    return i - (state & 5) - 5 * (state > 7);
+    return i - (state & 5);
 }
 
 static int scan_mmco_reset(AVCodecParserContext *s, GetBitContext *gb,