[FFmpeg-devel] [PATCH] libavformat/avc.c annexb parsing corrupts packets

[matteo.elli at m-elli.it]

Hi,

code in libavformat/avc.c is seldom executed but it surely does when you transmux (vcodec=copy) from h264 in a ts container to h264 in an mp4/mov/mkv/avi container.

The code there fails to handle annexb 00 00 01 NAL three byets prefixes properly and cuts the last byte in the previous NAL corrupting the whole frame.

Here is my proposed fix.

Index: libavformat/avc.c
===================================================================
--- libavformat/avc.c	(revision 19515)
+++ libavformat/avc.c	(working copy)
@@ -39,15 +39,15 @@
         if( (x - 0x01010101) & (~x) & 0x80808080 ) { // generic
             if( p[1] == 0 ) {
                 if( p[0] == 0 && p[2] == 1 )
-                    return p-1;
+                    return p;
                 if( p[2] == 0 && p[3] == 1 )
-                    return p;
+                    return p+1;
             }
             if( p[3] == 0 ) {
                 if( p[2] == 0 && p[4] == 1 )
-                    return p+1;
+                    return p+2;
                 if( p[4] == 0 && p[5] == 1 )
-                    return p+2;
+                    return p+3;
             }
         }
     }
@@ -69,8 +69,9 @@
     size = 0;
     nal_start = ff_avc_find_startcode(p, end);
     while (nal_start < end) {
-        while(!*(nal_start++));
+        while(nal_start < end && !*(nal_start++)); if(nal_start == end) break;
         nal_end = ff_avc_find_startcode(nal_start, end);
+		while(nal_end > nal_start && !*(nal_end - 1)) nal_end--;
         put_be32(pb, nal_end - nal_start);
         put_buffer(pb, nal_start, nal_end - nal_start);
         size += 4 + nal_end - nal_start;

----------

Matteo Elli  
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