commit f81ebc29c356fbaac9b361234b16b65fe92bbda4
author Wan-Teh Chang <wtc@google.com> Tue Apr 04 11:08:43 2023 -0700
committer GitHub <noreply@github.com> Tue Apr 04 11:08:43 2023 -0700
tree d303393626d3beaf66cd4bd68d6c0dc1af3fdccb
parent 2f092d3133a1dabf1bdbae02085965f7c8d90672

Do not create AV1 codecs in avifDecoderParse() (#814)

* Do not create AV1 codecs in avifDecoderParse()

The creation of AV1 codecs can be completely postponed to
avifDecoderNextImage().

This patch also removes avifDecoderFlush and replaces the calls
with avifDecoderDataResetCodec since both the functions are the
same in the new code.

Co-authored-by: Vignesh Venkatasubramanian <vigneshv@google.com>

src/read.c

diff --git a/src/read.c b/src/read.c
index 352eec6..7eecc1c 100644
--- a/src/read.c
+++ b/src/read.c
@@ -3342,22 +3342,6 @@
     return avifCodecCreate(choice, AVIF_CODEC_FLAG_CAN_DECODE);
 }
 
-static avifResult avifDecoderFlush(avifDecoder * decoder)
-{
-    avifDecoderDataResetCodec(decoder->data);
-
-    for (unsigned int i = 0; i < decoder->data->tiles.count; ++i) {
-        avifTile * tile = &decoder->data->tiles.tile[i];
-        tile->codec = avifCodecCreateInternal(decoder->codecChoice);
-        if (tile->codec) {
-            tile->codec->diag = &decoder->diag;
-            tile->codec->operatingPoint = tile->operatingPoint;
-            tile->codec->allLayers = tile->input->allLayers;
-        }
-    }
-    return AVIF_RESULT_OK;
-}
-
 // If alpha is AVIF_FALSE, searches for the primary color item (parentItemID is ignored in this case).
 // If alpha is AVIF_TRUE, searches for the auxiliary alpha item whose parent item ID is parentItemID.
 // Returns the target item if found, or NULL.
@@ -3811,7 +3795,7 @@
         return AVIF_RESULT_BMFF_PARSE_FAILED;
     }
 
-    return avifDecoderFlush(decoder);
+    return AVIF_RESULT_OK;
 }
 
 static avifResult avifDecoderPrepareTiles(avifDecoder * decoder, uint32_t nextImageIndex, const avifTileInfo * info)
@@ -3821,7 +3805,11 @@
 
         // Ensure there's an AV1 codec available before doing anything else
         if (!tile->codec) {
-            return AVIF_RESULT_NO_CODEC_AVAILABLE;
+            tile->codec = avifCodecCreateInternal(decoder->codecChoice);
+            AVIF_CHECKERR(tile->codec, AVIF_RESULT_NO_CODEC_AVAILABLE);
+            tile->codec->diag = &decoder->diag;
+            tile->codec->operatingPoint = tile->operatingPoint;
+            tile->codec->allLayers = tile->input->allLayers;
         }
 
         if (nextImageIndex >= tile->input->samples.count) {
@@ -4114,14 +4102,18 @@
         }
         // The next image (decoder->imageIndex + 1) is partially decoded but
         // the previous image (decoder->imageIndex) is requested.
-        // Fall through to flush and start decoding from the nearest key frame.
+        // Fall through to resetting the decoder data and start decoding from
+        // the nearest key frame.
     }
 
     int nearestKeyFrame = (int)avifDecoderNearestKeyframe(decoder, frameIndex);
     if ((nearestKeyFrame > (decoder->imageIndex + 1)) || (requestedIndex <= decoder->imageIndex)) {
-        // If we get here, a decoder flush is necessary
+        // If we get here, we need to start decoding from the nearest key frame.
+        // So discard the unused decoder state and its previous frames. This
+        // will force the setup of a new decoder instance in
+        // avifDecoderNextImage().
         decoder->imageIndex = nearestKeyFrame - 1; // prepare to read nearest keyframe
-        avifDecoderFlush(decoder);
+        avifDecoderDataResetCodec(decoder->data);
     }
     for (;;) {
         avifResult result = avifDecoderNextImage(decoder);