[FFmpeg-devel] [RFC] use ff_avc_find_startcode in ff_find_start_code

[Michael Niedermayer]

On Tue, Feb 19, 2008 at 10:05:03AM +0100, Reimar D?ffinger wrote:
> Hello,
> On Tue, Feb 19, 2008 at 03:57:07AM +0100, Michael Niedermayer wrote:
> > current code:
> > 7054 dezicycles in findsc, 262131 runs, 13 skips
> > 7082 dezicycles in findsc, 262134 runs, 10 skips
> > 
> > your code:
> > 11371 dezicycles in findsc, 262119 runs, 25 skips
> > 11624 dezicycles in findsc, 262115 runs, 29 skips
> > 
> > gcc: 4.3.0 20080127 (experimental)
> > 800mhz duron
> > ffmpeg -v 9 -i matrixbench_mpeg2.mpg -vcodec copy -an -y test.avi
> 
> Hmm... but like this it is only used in the demuxer code, right?

Its only used in the AVParser in the above. The decoder IIRC does only search
like 3 bytes or so unless you use multithreaded decoding. So if you didnt
use lavf for demuxing then i dont understand how you could see any difference
at all.


> How/where did you place the START_TIMER/STOP_TIMER?

-------
Index: libavcodec/mpegvideo.c
===================================================================
--- libavcodec/mpegvideo.c	(revision 11927)
+++ libavcodec/mpegvideo.c	(working copy)
@@ -97,6 +97,8 @@
     }
 }
 
+uint8_t *ff_avc_find_startcode(uint8_t *p, uint8_t *end);
+
 const uint8_t *ff_find_start_code(const uint8_t * restrict p, const uint8_t *end, uint32_t * restrict state){
     int i;
 
@@ -110,7 +112,12 @@
         if(tmp == 0x100 || p==end)
             return p;
     }
-
+{
+START_TIMER
+#if 1
+    p = ff_avc_find_startcode(p-3, end);
+    p = FFMIN(p + 4, end);
+#else
     while(p<end){
         if     (p[-1] > 1      ) p+= 3;
         else if(p[-2]          ) p+= 2;
@@ -120,6 +127,9 @@
             break;
         }
     }
+#endif
+STOP_TIMER("findsc")
+}
 
     p= FFMIN(p, end)-4;
     *state= AV_RB32(p);
---------

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Those who are too smart to engage in politics are punished by being
governed by those who are dumber. -- Plato 
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