Add IO stats to avif to see how large OBUs are after read/write

include/avif/avif.h

diff --git a/include/avif/avif.h b/include/avif/avif.h
index 5fd3471..4b1953b 100644
--- a/include/avif/avif.h
+++ b/include/avif/avif.h
@@ -281,6 +281,13 @@
     avifProfileFormat profileFormat;
     avifRawData icc;
     avifNclxColorProfile nclx;
+
+    // Useful stats from the most recent read/write
+    struct IOStats
+    {
+        size_t colorOBUSize;
+        size_t alphaOBUSize;
+    } ioStats;
 } avifImage;
 
 avifImage * avifImageCreate(int width, int height, int depth, avifPixelFormat yuvFormat);

src/read.c

diff --git a/src/read.c b/src/read.c
index 7f5d03e..c87a079 100644
--- a/src/read.c
+++ b/src/read.c
@@ -707,5 +707,8 @@
     if (codec) {
         avifCodecDestroy(codec);
     }
+
+    image->ioStats.colorOBUSize = colorOBU.size;
+    image->ioStats.alphaOBUSize = alphaOBU.size;
     return AVIF_RESULT_OK;
 }

src/write.c

diff --git a/src/write.c b/src/write.c
index 9719a7b..700867e 100644
--- a/src/write.c
+++ b/src/write.c
@@ -285,6 +285,13 @@
 
     avifStreamFinishBox(&s, meta);
     avifStreamFinishWrite(&s);
+
+    // -----------------------------------------------------------------------
+    // IO stats
+
+    image->ioStats.colorOBUSize = colorOBU.size;
+    image->ioStats.alphaOBUSize = alphaOBU.size;
+
     result = AVIF_RESULT_OK;
 
     // -----------------------------------------------------------------------