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

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

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@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,

Will apply this patchset tomorrow unless there are objections.

- Andreas

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