[FFmpeg-devel] [PATCH 2/2] avfilter/scale_vt: implement frame crop

[Zhao Zhili]

> On Nov 25, 2024, at 12:48, Koushik Dutta <koushd at gmail.com> wrote:
> 
> The crop filter has no effect on scale_vt:
> 
> -vf crop=100:100,scale_vt=300x300
> 
> Hardware frames (AV_PIX_FMT_FLAG_HWACCEL) are expected to use the crop_* properties,
> as seen in the implementation vf_crop.c.
> 
> The current workaround is to hwdownload the full frame
> and perform the crop on CPU.
> 
> Signed-off-by: Koushik Dutta <koushd at gmail.com>

Patchset pushed, thanks. Sorry for the delay.

> ---
> libavfilter/vf_scale_vt.c | 55 +++++++++++++++++++++++++++++++++++++++
> 1 file changed, 55 insertions(+)
> 
> diff --git a/libavfilter/vf_scale_vt.c b/libavfilter/vf_scale_vt.c
> index 07d825b1ba..eff23a6f39 100644
> --- a/libavfilter/vf_scale_vt.c
> +++ b/libavfilter/vf_scale_vt.c
> @@ -109,6 +109,8 @@ static av_cold int scale_vt_init(AVFilterContext *avctx)
>         VTSessionSetProperty(s->transfer, kVTPixelTransferPropertyKey_DestinationYCbCrMatrix, value);
>     }
> 
> +    VTSessionSetProperty(s->transfer, kVTPixelTransferPropertyKey_ScalingMode, kVTScalingMode_CropSourceToCleanAperture);
> +
>     return 0;
> }
> 
> @@ -132,6 +134,18 @@ static int scale_vt_filter_frame(AVFilterLink *link, AVFrame *in)
>     CVPixelBufferRef src;
>     CVPixelBufferRef dst;
> 
> +    int left;
> +    int top;
> +    int width;
> +    int height;
> +    CFNumberRef crop_width_num;
> +    CFNumberRef crop_height_num;
> +    CFNumberRef crop_offset_left_num;
> +    CFNumberRef crop_offset_top_num;
> +    const void *clean_aperture_keys[4];
> +    const void *source_clean_aperture_values[4];
> +    CFDictionaryRef source_clean_aperture;
> +
>     AVFrame *out = ff_get_video_buffer(outlink, outlink->w, outlink->h);
>     if (!out) {
>         ret = AVERROR(ENOMEM);
> @@ -142,6 +156,11 @@ static int scale_vt_filter_frame(AVFilterLink *link, AVFrame *in)
>     if (ret < 0)
>         goto fail;
> 
> +    out->crop_left = 0;
> +    out->crop_top = 0;
> +    out->crop_right = 0;
> +    out->crop_bottom = 0;
> +
>     av_reduce(&out->sample_aspect_ratio.num, &out->sample_aspect_ratio.den,
>               (int64_t)in->sample_aspect_ratio.num * outlink->h * link->w,
>               (int64_t)in->sample_aspect_ratio.den * outlink->w * link->h,
> @@ -153,9 +172,45 @@ static int scale_vt_filter_frame(AVFilterLink *link, AVFrame *in)
>     if (s->colour_matrix != AVCOL_SPC_UNSPECIFIED)
>         out->colorspace = s->colour_matrix;
> 
> +    width = (in->width - in->crop_right) - in->crop_left;
> +    height = (in->height - in->crop_bottom) - in->crop_top;
> +    // The crop offsets are relative to the center of the frame.
> +    // the crop width and crop height are relative to the center of the crop rect, not top left as normal.
> +    left = in->crop_left - in->width / 2 + width / 2;
> +    top = in->crop_top - in->height / 2 + height / 2;
> +    crop_width_num = CFNumberCreate(kCFAllocatorDefault, kCFNumberIntType, &width);
> +    crop_height_num = CFNumberCreate(kCFAllocatorDefault, kCFNumberIntType, &height);
> +    crop_offset_left_num = CFNumberCreate(kCFAllocatorDefault, kCFNumberIntType, &left);
> +    crop_offset_top_num = CFNumberCreate(kCFAllocatorDefault, kCFNumberIntType, &top);
> +
> +    clean_aperture_keys[0] = kCVImageBufferCleanApertureWidthKey;
> +    clean_aperture_keys[1] = kCVImageBufferCleanApertureHeightKey;
> +    clean_aperture_keys[2] = kCVImageBufferCleanApertureHorizontalOffsetKey;
> +    clean_aperture_keys[3] = kCVImageBufferCleanApertureVerticalOffsetKey;
> +
> +    source_clean_aperture_values[0] = crop_width_num;
> +    source_clean_aperture_values[1] = crop_height_num;
> +    source_clean_aperture_values[2] = crop_offset_left_num;
> +    source_clean_aperture_values[3] = crop_offset_top_num;
> +
> +    source_clean_aperture = CFDictionaryCreate(kCFAllocatorDefault,
> +                                                    clean_aperture_keys,
> +                                                    source_clean_aperture_values,
> +                                                    4,
> +                                                    &kCFTypeDictionaryKeyCallBacks,
> +                                                    &kCFTypeDictionaryValueCallBacks);
> +
> +    CFRelease(crop_width_num);
> +    CFRelease(crop_height_num);
> +    CFRelease(crop_offset_left_num);
> +    CFRelease(crop_offset_top_num);
> +
>     src = (CVPixelBufferRef)in->data[3];
>     dst = (CVPixelBufferRef)out->data[3];
> +    CVBufferSetAttachment(src, kCVImageBufferCleanApertureKey,
> +                           source_clean_aperture, kCVAttachmentMode_ShouldPropagate);
>     ret = VTPixelTransferSessionTransferImage(s->transfer, src, dst);
> +    CFRelease(source_clean_aperture);
>     if (ret != noErr) {
>         av_log(ctx, AV_LOG_ERROR, "transfer image failed, %d\n", ret);
>         ret = AVERROR_EXTERNAL;
> -- 
> 2.39.5 (Apple Git-154)
> 
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