[FFmpeg-devel] [PATCH] lavc/mjpegdec: speed up scan data copy

[Matthieu Bouron]

From: Matthieu Bouron <matthieu.bouron at stupeflix.com>

---

>From random 3264x2448 jpegs, scan data copy on a Nexus5 goes from [15, 28]ms to [3, 12]ms.

---
 libavcodec/mjpegdec.c | 43 +++++++++++++++++++++++++++++++++----------
 1 file changed, 33 insertions(+), 10 deletions(-)

diff --git a/libavcodec/mjpegdec.c b/libavcodec/mjpegdec.c
index 863738d..9a501d2 100644
--- a/libavcodec/mjpegdec.c
+++ b/libavcodec/mjpegdec.c
@@ -1917,24 +1917,47 @@ int ff_mjpeg_find_marker(MJpegDecodeContext *s,
     /* unescape buffer of SOS, use special treatment for JPEG-LS */
     if (start_code == SOS && !s->ls) {
         const uint8_t *src = *buf_ptr;
+        const uint8_t *ptr = src;
         uint8_t *dst = s->buffer;
 
-        while (src < buf_end) {
-            uint8_t x = *(src++);
+        #define copy_data_segment(skipped) do {       \
+            ssize_t length = (ptr - src) - (skipped); \
+            if (length > 0) {                         \
+                memcpy(dst, src, length);             \
+                dst += length;                        \
+                src = ptr;                            \
+            }                                         \
+        } while (0)
+
+        if (s->avctx->codec_id == AV_CODEC_ID_THP) {
+            ptr = buf_end;
+            copy_data_segment(0);
+        } else {
+            while (ptr < buf_end) {
+                uint8_t x = *(ptr++);
 
-            *(dst++) = x;
-            if (s->avctx->codec_id != AV_CODEC_ID_THP) {
                 if (x == 0xff) {
-                    while (src < buf_end && x == 0xff)
-                        x = *(src++);
+                    ssize_t skipped = -1;
+                    while (ptr < buf_end && x == 0xff) {
+                        x = *(ptr++);
+                        skipped++;
+                    }
 
-                    if (x >= 0xd0 && x <= 0xd7)
-                        *(dst++) = x;
-                    else if (x)
-                        break;
+                    if (skipped > 0)
+                        copy_data_segment(skipped);
+
+                    if (x < 0xd0 || x > 0xd7) {
+                        copy_data_segment(1);
+                        if (x)
+                            break;
+                    }
                 }
             }
+            if (src < ptr)
+                copy_data_segment(0);
         }
+        #undef copy_data_segment
+
         *unescaped_buf_ptr  = s->buffer;
         *unescaped_buf_size = dst - s->buffer;
         memset(s->buffer + *unescaped_buf_size, 0,
-- 
2.7.0