Re: [FFmpeg-devel] [PATCH] avutil/imgutils: optimize image copy efficiency

["Martin Storsjö" <martin@martin.st>]

On Thu, 4 May 2023, xufuji456 wrote:

> It makes sense when copying 4K/8K video, if linesize
> equals to aligned linesize.
>
> Signed-off-by: xufuji456 <839789740@qq.com>
> ---
> libavutil/imgutils.c | 15 +++++++++++----
> 1 file changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/libavutil/imgutils.c b/libavutil/imgutils.c
> index 9ab5757cf6..1d432e7a57 100644
> --- a/libavutil/imgutils.c
> +++ b/libavutil/imgutils.c
> @@ -525,10 +525,17 @@ int av_image_copy_to_buffer(uint8_t *dst, int dst_size,
>         const uint8_t *src = src_data[i];
>         h = (height + (1 << shift) - 1) >> shift;
>
> -        for (j = 0; j < h; j++) {
> -            memcpy(dst, src, linesize[i]);
> -            dst += FFALIGN(linesize[i], align);
> -            src += src_linesize[i];
> +        if (FFALIGN(linesize[i], align) == linesize[i] && src_linesize[i] == linesize[i]) {
> +            int size = linesize[i] * h;

For cases like these, I would prefer to use "linesize[i] * (h - 1) + w" 
instead. For cases if copying e.g. into an offsetted position within a 
buffer, writing the last trailing padding would end up writing out of 
bounds.

That said, I'm unsure about how much gain you get from this optimization 
here - some numbers to back it up would be useful.

// Martin

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