[Ffmpeg-devel] Speed improvement for jpeg decoding

[Cyril Russo]

Hi,

 Like diego said, here is a patch to speed up jpeg decoding by avoiding 
a conditional test for each macroblock in a JPEG stream.
Like Michael said, I've tried to keep it as short as possible.

--- ../../mjpeg.c       2006-11-21 12:22:21.000000000 +0100
+++ mjpeg.c     2006-11-21 12:47:29.000000000 +0100
@@ -1565,9 +1565,19 @@ static int ljpeg_decode_yuv_scan(MJpegDe
     return 0;
 }

+/* decode block and dequantize - not progressive JPEG version wrapper */
+inline static int decode_block_notprogressive(MJpegDecodeContext *s, 
DCTELEM *block,
+                        int component, int dc_index, int ac_index, 
int16_t *quant_matrix,
+                        int ss, int se, int Ah, int Al, int *EOBRUN)
+{
+    return decode_block(s, block, component, dc_index, ac_index, 
quant_matrix);
+}
+
 static int mjpeg_decode_scan(MJpegDecodeContext *s, int nb_components, 
int ss, int se, int Ah, int Al){
     int i, mb_x, mb_y;
     int EOBRUN = 0;
+    int (*pdecode)(MJpegDecodeContext *, DCTELEM *, int, int, int, 
int16_t *, int, int, int, int, int *) = s->progressive ? 
decode_block_progressive : decode_block_notprogressive;
+    void (*pidct)(uint8_t *, int, DCTELEM *) = s->progressive ? 
s->idct_add : s->idct_put;

     if(Ah) return 0; /* TODO decode refinement planes too */
     for(mb_y = 0; mb_y < s->mb_height; mb_y++) {
@@ -1586,13 +1596,7 @@ static int mjpeg_decode_scan(MJpegDecode
                 y = 0;
                 for(j=0;j<n;j++) {
                     memset(s->block, 0, sizeof(s->block));
-                    if (!s->progressive && decode_block(s, s->block, i,
-                                     s->dc_index[i], s->ac_index[i],
-                                     s->quant_matrixes[ 
s->quant_index[c] ]) < 0) {
-                        dprintf("error y=%d x=%d\n", mb_y, mb_x);
-                        return -1;
-                    }
-                    if (s->progressive && decode_block_progressive(s, 
s->block, i,
+                    if (pdecode(s, s->block, i,
                                      s->dc_index[i], s->ac_index[i],
                                      s->quant_matrixes[ 
s->quant_index[c] ], ss, se, Ah, Al, &EOBRUN) < 0) {
                         dprintf("error y=%d x=%d\n", mb_y, mb_x);
@@ -1605,10 +1609,7 @@ static int mjpeg_decode_scan(MJpegDecode
                     if (s->interlaced && s->bottom_field)
                         ptr += s->linesize[c] >> 1;
 //av_log(NULL, AV_LOG_DEBUG, "%d %d %d %d %d %d %d %d \n", mb_x, mb_y, 
x, y, c, s->bottom_field, (v * mb_y + y) * 8, (h * mb_x + x) * 8);
-                    if(!s->progressive)
-                        s->idct_put(ptr, s->linesize[c], s->block);
-                    else
-                        s->idct_add(ptr, s->linesize[c], s->block);
+                    pidct(ptr, s->linesize[c], s->block);
                     if (++x == h) {
                         x = 0;
                         y++;

-- 
Cyril RUSSO