[FFmpeg-devel] [PATCH v2 1/6] avcodec/flashsvenc: Fix packet size calculation

[Andreas Rheinhardt]

The earlier code did not account for the frame header as well
as the block headers; furthermore, in case a large part of
a block is unused (due to padding), the output size may
exceed 3 * width * height (where the dimensions correspond
to the visible pixels) due to the overhead of the zlib header,
so use the padded dimensions to calculate the maximum packet size
(which is also what the actual call to compress2() uses).
Fixes ticket #10053.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at outlook.com>
---
 libavcodec/flashsvenc.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/libavcodec/flashsvenc.c b/libavcodec/flashsvenc.c
index 35793400fa..4cedb53fe4 100644
--- a/libavcodec/flashsvenc.c
+++ b/libavcodec/flashsvenc.c
@@ -54,11 +54,15 @@
 #include "put_bits.h"
 #include "bytestream.h"
 
+/* These values are hardcoded for now. */
+#define BLOCK_WIDTH  (4 * 16U)
+#define BLOCK_HEIGHT (4 * 16U)
 
 typedef struct FlashSVContext {
     AVCodecContext *avctx;
     uint8_t        *previous_frame;
     int             image_width, image_height;
+    unsigned        packet_size;
     int             block_width, block_height;
     uint8_t        *encbuffer;
     int             block_size;
@@ -100,6 +104,7 @@ static av_cold int flashsv_encode_end(AVCodecContext *avctx)
 static av_cold int flashsv_encode_init(AVCodecContext *avctx)
 {
     FlashSVContext *s = avctx->priv_data;
+    int h_blocks, v_blocks, nb_blocks;
 
     s->avctx = avctx;
 
@@ -114,6 +119,11 @@ static av_cold int flashsv_encode_init(AVCodecContext *avctx)
     s->image_width  = avctx->width;
     s->image_height = avctx->height;
 
+    h_blocks = (s->image_width  + BLOCK_WIDTH - 1) / BLOCK_WIDTH;
+    v_blocks = (s->image_height + BLOCK_WIDTH - 1) / BLOCK_WIDTH;
+    nb_blocks = h_blocks * v_blocks;
+    s->packet_size = 4 + nb_blocks * (2 + 3 * BLOCK_WIDTH * BLOCK_HEIGHT);
+
     s->encbuffer = av_mallocz(s->image_width * s->image_height * 3);
 
     if (!s->encbuffer) {
@@ -229,7 +239,8 @@ static int flashsv_encode_frame(AVCodecContext *avctx, AVPacket *pkt,
         I_frame = 1;
     }
 
-    if ((res = ff_alloc_packet(avctx, pkt, s->image_width * s->image_height * 3)) < 0)
+    res = ff_alloc_packet(avctx, pkt, s->packet_size);
+    if (res < 0)
         return res;
 
     pkt->size = encode_bitstream(s, p, pkt->data, pkt->size, opt_w * 16, opt_h * 16,
-- 
2.34.1