Allow to override zlib compression level in PNG encoder via avctx->compression_level

Originally committed as revision 10699 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/pngenc.c

@@ -144,6 +144,7 @@ static int encode_frame(AVCodecContext *avctx, unsigned char *buf, int buf_size,
     AVFrame * const p= (AVFrame*)&s->picture;
     int bit_depth, color_type, y, len, row_size, ret, is_progressive;
     int bits_per_pixel, pass_row_size;
+    int compression_level;
     uint8_t *ptr;
     uint8_t *crow_buf = NULL;
     uint8_t *tmp_buf = NULL;
@@ -187,7 +188,10 @@ static int encode_frame(AVCodecContext *avctx, unsigned char *buf, int buf_size,
     s->zstream.zalloc = ff_png_zalloc;
     s->zstream.zfree = ff_png_zfree;
     s->zstream.opaque = NULL;
-    ret = deflateInit2(&s->zstream, Z_DEFAULT_COMPRESSION,
+    compression_level = avctx->compression_level == FF_COMPRESSION_DEFAULT ?
+                            Z_DEFAULT_COMPRESSION :
+                            av_clip(avctx->compression_level, 0, 9);
+    ret = deflateInit2(&s->zstream, compression_level,
                        Z_DEFLATED, 15, 8, Z_DEFAULT_STRATEGY);
     if (ret != Z_OK)
         return -1;