Re: [FFmpeg-devel] [PATCH 6/7] avfilter/alphadetect_vulkan: add alpha type detection filter

[Niklas Haas <ffmpeg@haasn.xyz>]

On Sun, 18 May 2025 14:11:51 +0200 Niklas Haas <ffmpeg@haasn.xyz> wrote:
> From: Niklas Haas <git@haasn.dev>
>
> This determines whether the input has any pixel values exceeding the alpha
> channel. In this case, we can be sure that the input is not premultiplied.
> In all other cases, the result in indeterminate. As such, we can only have
> false negatives, but no false positives.

I will drop this patch and resumbit it alongside a C implementation as a more
general purpose "detect color properties" filter, which will also be able to
auto-detect YUV range.

>
> Signed-off-by: Niklas Haas <git@haasn.dev>
> Sponsored-by: nxtedition
> ---
>  configure                           |   1 +
>  libavfilter/Makefile                |   1 +
>  libavfilter/allfilters.c            |   1 +
>  libavfilter/vf_alphadetect_vulkan.c | 400 ++++++++++++++++++++++++++++
>  4 files changed, 403 insertions(+)
>  create mode 100644 libavfilter/vf_alphadetect_vulkan.c
>
> diff --git a/configure b/configure
> index 2e5f9fea49..9556d7c86f 100755
> --- a/configure
> +++ b/configure
> @@ -3869,6 +3869,7 @@ libzmq_protocol_deps="libzmq"
>  libzmq_protocol_select="network"
>
>  # filters
> +alphadetect_vulkan_filter_deps="vulkan spirv_compiler"
>  ametadata_filter_deps="avformat"
>  amovie_filter_deps="avcodec avformat"
>  aresample_filter_deps="swresample"
> diff --git a/libavfilter/Makefile b/libavfilter/Makefile
> index e9d4566a2a..76a4f53932 100644
> --- a/libavfilter/Makefile
> +++ b/libavfilter/Makefile
> @@ -192,6 +192,7 @@ OBJS-$(CONFIG_ANULLSINK_FILTER)              += asink_anullsink.o
>
>  # video filters
>  OBJS-$(CONFIG_ADDROI_FILTER)                 += vf_addroi.o
> +OBJS-$(CONFIG_ALPHADETECT_VULKAN_FILTER)     += vf_alphadetect_vulkan.o
>  OBJS-$(CONFIG_ALPHAEXTRACT_FILTER)           += vf_extractplanes.o
>  OBJS-$(CONFIG_ALPHAMERGE_FILTER)             += vf_alphamerge.o framesync.o
>  OBJS-$(CONFIG_AMPLIFY_FILTER)                += vf_amplify.o
> diff --git a/libavfilter/allfilters.c b/libavfilter/allfilters.c
> index 92890575f1..88204e070c 100644
> --- a/libavfilter/allfilters.c
> +++ b/libavfilter/allfilters.c
> @@ -177,6 +177,7 @@ extern const FFFilter ff_asrc_sine;
>  extern const FFFilter ff_asink_anullsink;
>
>  extern const FFFilter ff_vf_addroi;
> +extern const FFFilter ff_vf_alphadetect_vulkan;
>  extern const FFFilter ff_vf_alphaextract;
>  extern const FFFilter ff_vf_alphamerge;
>  extern const FFFilter ff_vf_amplify;
> diff --git a/libavfilter/vf_alphadetect_vulkan.c b/libavfilter/vf_alphadetect_vulkan.c
> new file mode 100644
> index 0000000000..ed76671fc1
> --- /dev/null
> +++ b/libavfilter/vf_alphadetect_vulkan.c
> @@ -0,0 +1,400 @@
> +/*
> + * Copyright 2025 (c) Niklas Haas
> + *
> + * This file is part of FFmpeg.
> + *
> + * FFmpeg is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * FFmpeg is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with FFmpeg; if not, write to the Free Software
> + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
> + */
> +
> +#include <float.h>
> +#include "libavutil/vulkan_spirv.h"
> +#include "libavutil/opt.h"
> +#include "libavutil/timestamp.h"
> +#include "vulkan_filter.h"
> +
> +#include "drawutils.h"
> +#include "filters.h"
> +#include "video.h"
> +
> +enum AlphaType {
> +    UNDETERMINED = 0,
> +    STRAIGHT,
> +    NONE,
> +};
> +
> +static const char *type2str(enum AlphaType type)
> +{
> +    switch(type) {
> +        case NONE         : return "none";
> +        case STRAIGHT     : return "straight";
> +        case UNDETERMINED : return "undetermined";
> +    }
> +    return NULL;
> +}
> +
> +typedef struct AlphaDetectVulkanContext {
> +    FFVulkanContext vkctx;
> +
> +    int initialized;
> +    FFVkExecPool e;
> +    AVVulkanDeviceQueueFamily *qf;
> +    FFVulkanShader shd;
> +    AVBufferPool *det_buf_pool;
> +
> +    enum AlphaType type;
> +} AlphaDetectVulkanContext;
> +
> +typedef struct AlphaDetectPushData {
> +    float yscale, yoff;
> +} AlphaDetectPushData;
> +
> +typedef struct AlphaDetectBuf {
> +    uint32_t frame_straight;
> +} AlphaDetectBuf;
> +
> +static void fmt_swizzle(FFVulkanShader *shd, enum AVPixelFormat fmt)
> +{
> +    const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(fmt);
> +    uint8_t map[4];
> +    char swiz[5] = {0};
> +
> +    if (desc->flags & AV_PIX_FMT_FLAG_RGB) {
> +        ff_fill_rgba_map(map, fmt);
> +    } else if (desc->nb_components == 2) { /* ya */
> +        GLSLC(1, color.a = color.y;);
> +        return;
> +    } else {
> +        ff_fill_ayuv_map(map, fmt);
> +    }
> +
> +    for (int i = 0; i < 4; i++)
> +        swiz[i] = "rgba"[map[i]];
> +
> +    GLSLF(1, color = color.%s; ,swiz);
> +}
> +
> +static av_cold int init_filter(AVFilterContext *ctx)
> +{
> +    int err;
> +    uint8_t *spv_data;
> +    size_t spv_len;
> +    void *spv_opaque = NULL;
> +    AlphaDetectVulkanContext *s = ctx->priv;
> +    FFVulkanContext *vkctx = &s->vkctx;
> +    FFVulkanShader *shd;
> +    FFVkSPIRVCompiler *spv;
> +    FFVulkanDescriptorSetBinding *desc;
> +
> +    const int planes = av_pix_fmt_count_planes(s->vkctx.input_format);
> +    const AVPixFmtDescriptor *pixdesc = av_pix_fmt_desc_get(s->vkctx.input_format);
> +    if (!(pixdesc->flags & AV_PIX_FMT_FLAG_ALPHA)) { /* nothing to do */
> +        s->initialized = 1;
> +        s->type = NONE;
> +        return 0;
> +    }
> +
> +    spv = ff_vk_spirv_init();
> +    if (!spv) {
> +        av_log(ctx, AV_LOG_ERROR, "Unable to initialize SPIR-V compiler!\n");
> +        return AVERROR_EXTERNAL;
> +    }
> +
> +    s->qf = ff_vk_qf_find(vkctx, VK_QUEUE_COMPUTE_BIT, 0);
> +    if (!s->qf) {
> +        av_log(ctx, AV_LOG_ERROR, "Device has no compute queues\n");
> +        err = AVERROR(ENOTSUP);
> +        goto fail;
> +    }
> +
> +    RET(ff_vk_exec_pool_init(vkctx, s->qf, &s->e, s->qf->num*4, 0, 0, 0, NULL));
> +    RET(ff_vk_shader_init(vkctx, &s->shd, "alphadetect",
> +                          VK_SHADER_STAGE_COMPUTE_BIT,
> +                          (const char *[]) { "GL_KHR_shader_subgroup_vote" }, 1,
> +                          32, 32, 1,
> +                          0));
> +    shd = &s->shd;
> +
> +    GLSLC(0, layout(push_constant, std430) uniform pushConstants {            );
> +    GLSLC(1,     float yscale;                                                );
> +    GLSLC(1,     float yoff;                                                  );
> +    GLSLC(0, };                                                               );
> +
> +    ff_vk_shader_add_push_const(shd, 0, sizeof(AlphaDetectPushData),
> +                                VK_SHADER_STAGE_COMPUTE_BIT);
> +
> +    desc = (FFVulkanDescriptorSetBinding []) {
> +        {
> +            .name       = "input_img",
> +            .type       = VK_DESCRIPTOR_TYPE_STORAGE_IMAGE,
> +            .mem_layout = ff_vk_shader_rep_fmt(s->vkctx.input_format, FF_VK_REP_FLOAT),
> +            .mem_quali  = "readonly",
> +            .dimensions = 2,
> +            .elems      = av_pix_fmt_count_planes(s->vkctx.input_format),
> +            .stages     = VK_SHADER_STAGE_COMPUTE_BIT,
> +        }, {
> +            .name        = "det_buffer",
> +            .type        = VK_DESCRIPTOR_TYPE_STORAGE_BUFFER,
> +            .stages      = VK_SHADER_STAGE_COMPUTE_BIT,
> +            .buf_content = "uint frame_straight;",
> +        }
> +    };
> +
> +    RET(ff_vk_shader_add_descriptor_set(vkctx, &s->shd, desc, 2, 0, 0));
> +
> +    GLSLC(0, void main()                                                      );
> +    GLSLC(0, {                                                                );
> +    GLSLC(1,     const ivec2 pos = ivec2(gl_GlobalInvocationID.xy);           );
> +    GLSLC(1,     if (!IS_WITHIN(pos, imageSize(input_img[0])))                );
> +    GLSLC(2,         return;                                                  );
> +
> +    GLSLC(1, vec4 color = imageLoad(input_img[0],  pos);                      );
> +    for (int i = 1; i < planes; i++) {
> +        const int idx = planes == 2 ? 3 : i;
> +        if (!(pixdesc->flags & AV_PIX_FMT_FLAG_RGB) && idx != 3)
> +            continue; /* skip loading chroma */
> +        GLSLF(1, color[%d] = imageLoad(input_img[%d], pos).x;           ,idx,i);
> +    }
> +    fmt_swizzle(shd, s->vkctx.input_format);
> +    if (pixdesc->flags & AV_PIX_FMT_FLAG_RGB)
> +        GLSLC(1, bool straight = any(greaterThan(color.rgb, color.a));        );
> +    else
> +        GLSLC(1, bool straight = yscale * color.x + yoff > color.a;           );
> +    GLSLC(1,     if (subgroupAny(straight) && subgroupElect())                );
> +    GLSLC(2,         frame_straight = 1u;                                     );
> +    GLSLC(0, }                                                                );
> +
> +    RET(spv->compile_shader(vkctx, spv, &s->shd, &spv_data, &spv_len, "main",
> +                            &spv_opaque));
> +    RET(ff_vk_shader_link(vkctx, &s->shd, spv_data, spv_len, "main"));
> +
> +    RET(ff_vk_shader_register_exec(vkctx, &s->e, &s->shd));
> +
> +    s->initialized = 1;
> +
> +fail:
> +    if (spv_opaque)
> +        spv->free_shader(spv, &spv_opaque);
> +    if (spv)
> +        spv->uninit(&spv);
> +
> +    return err;
> +}
> +
> +static int alphadetect_vulkan_filter_frame(AVFilterLink *link, AVFrame *in)
> +{
> +    int err;
> +    AVFilterContext *ctx = link->dst;
> +    AlphaDetectVulkanContext *s = ctx->priv;
> +    AVFilterLink *outlink = ctx->outputs[0];
> +
> +    VkImageView in_views[AV_NUM_DATA_POINTERS];
> +    VkImageMemoryBarrier2 img_bar[4];
> +    int nb_img_bar = 0;
> +
> +    FFVulkanContext *vkctx = &s->vkctx;
> +    FFVulkanFunctions *vk = &vkctx->vkfn;
> +    FFVkExecContext *exec = NULL;
> +    AVBufferRef *sum_buf = NULL;
> +    FFVkBuffer *sum_vk;
> +
> +    AlphaDetectBuf *det;
> +    AlphaDetectPushData push_data;
> +
> +    if (in->color_range == AVCOL_RANGE_JPEG) {
> +        push_data.yscale = 1.0f;
> +        push_data.yoff   = 0.0f;
> +    } else {
> +        const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(vkctx->input_format);
> +        const int depth = desc->comp[0].depth;
> +        const int ymin = 16  << (depth - 8);
> +        const int ymax = 235 << (depth - 8);
> +        const int imax = (1 << depth) - 1;
> +        push_data.yscale = (float) imax / (ymax - ymin);
> +        push_data.yoff = push_data.yscale * -ymin / (float) imax;
> +    }
> +
> +    if (!s->initialized)
> +        RET(init_filter(ctx));
> +
> +    if (s->type != UNDETERMINED)
> +        return ff_filter_frame(outlink, in);
> +
> +    RET(ff_vk_get_pooled_buffer(vkctx, &s->det_buf_pool, &sum_buf,
> +                                VK_BUFFER_USAGE_TRANSFER_DST_BIT |
> +                                VK_BUFFER_USAGE_STORAGE_BUFFER_BIT,
> +                                NULL,
> +                                sizeof(AlphaDetectBuf),
> +                                VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT |
> +                                VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT |
> +                                VK_MEMORY_PROPERTY_HOST_COHERENT_BIT));
> +    sum_vk = (FFVkBuffer *)sum_buf->data;
> +    det = (AlphaDetectBuf *) sum_vk->mapped_mem;
> +
> +    exec = ff_vk_exec_get(vkctx, &s->e);
> +    ff_vk_exec_start(vkctx, exec);
> +
> +    RET(ff_vk_exec_add_dep_frame(vkctx, exec, in,
> +                                 VK_PIPELINE_STAGE_2_ALL_COMMANDS_BIT,
> +                                 VK_PIPELINE_STAGE_2_COMPUTE_SHADER_BIT));
> +    RET(ff_vk_create_imageviews(vkctx, exec, in_views, in, FF_VK_REP_FLOAT));
> +
> +    ff_vk_shader_update_img_array(vkctx, exec, &s->shd, in, in_views, 0, 0,
> +                                  VK_IMAGE_LAYOUT_GENERAL, VK_NULL_HANDLE);
> +
> +    ff_vk_frame_barrier(vkctx, exec, in, img_bar, &nb_img_bar,
> +                        VK_PIPELINE_STAGE_2_ALL_COMMANDS_BIT,
> +                        VK_PIPELINE_STAGE_2_COMPUTE_SHADER_BIT,
> +                        VK_ACCESS_SHADER_READ_BIT,
> +                        VK_IMAGE_LAYOUT_GENERAL,
> +                        VK_QUEUE_FAMILY_IGNORED);
> +
> +    /* zero det buffer */
> +    vk->CmdPipelineBarrier2(exec->buf, &(VkDependencyInfo) {
> +            .sType = VK_STRUCTURE_TYPE_DEPENDENCY_INFO,
> +            .pBufferMemoryBarriers = &(VkBufferMemoryBarrier2) {
> +                .sType = VK_STRUCTURE_TYPE_BUFFER_MEMORY_BARRIER_2,
> +                .srcStageMask = VK_PIPELINE_STAGE_2_NONE,
> +                .dstStageMask = VK_PIPELINE_STAGE_2_TRANSFER_BIT,
> +                .dstAccessMask = VK_ACCESS_TRANSFER_WRITE_BIT,
> +                .srcQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED,
> +                .dstQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED,
> +                .buffer = sum_vk->buf,
> +                .size = sum_vk->size,
> +                .offset = 0,
> +            },
> +            .bufferMemoryBarrierCount = 1,
> +        });
> +
> +    vk->CmdFillBuffer(exec->buf, sum_vk->buf, 0, sum_vk->size, 0x0);
> +
> +    vk->CmdPipelineBarrier2(exec->buf, &(VkDependencyInfo) {
> +            .sType = VK_STRUCTURE_TYPE_DEPENDENCY_INFO,
> +            .pImageMemoryBarriers = img_bar,
> +            .imageMemoryBarrierCount = nb_img_bar,
> +            .pBufferMemoryBarriers = &(VkBufferMemoryBarrier2) {
> +                .sType = VK_STRUCTURE_TYPE_BUFFER_MEMORY_BARRIER_2,
> +                .srcStageMask = VK_PIPELINE_STAGE_2_TRANSFER_BIT,
> +                .dstStageMask = VK_PIPELINE_STAGE_2_COMPUTE_SHADER_BIT,
> +                .srcAccessMask = VK_ACCESS_TRANSFER_WRITE_BIT,
> +                .dstAccessMask = VK_ACCESS_2_SHADER_STORAGE_WRITE_BIT,
> +                .srcQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED,
> +                .dstQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED,
> +                .buffer = sum_vk->buf,
> +                .size = sum_vk->size,
> +                .offset = 0,
> +            },
> +            .bufferMemoryBarrierCount = 1,
> +        });
> +
> +    RET(ff_vk_shader_update_desc_buffer(&s->vkctx, exec, &s->shd, 0, 1, 0,
> +                                        sum_vk, 0, sum_vk->size,
> +                                        VK_FORMAT_UNDEFINED));
> +
> +    ff_vk_exec_bind_shader(vkctx, exec, &s->shd);
> +    ff_vk_shader_update_push_const(vkctx, exec, &s->shd, VK_SHADER_STAGE_COMPUTE_BIT,
> +                                   0, sizeof(push_data), &push_data);
> +
> +    vk->CmdDispatch(exec->buf,
> +                    FFALIGN(in->width,  s->shd.lg_size[0]) / s->shd.lg_size[0],
> +                    FFALIGN(in->height, s->shd.lg_size[1]) / s->shd.lg_size[1],
> +                    s->shd.lg_size[2]);
> +
> +    vk->CmdPipelineBarrier2(exec->buf, &(VkDependencyInfo) {
> +            .sType = VK_STRUCTURE_TYPE_DEPENDENCY_INFO,
> +            .pBufferMemoryBarriers = &(VkBufferMemoryBarrier2) {
> +                .sType = VK_STRUCTURE_TYPE_BUFFER_MEMORY_BARRIER_2,
> +                .srcStageMask = VK_PIPELINE_STAGE_2_COMPUTE_SHADER_BIT,
> +                .dstStageMask = VK_PIPELINE_STAGE_2_HOST_BIT,
> +                .srcAccessMask = VK_ACCESS_2_SHADER_STORAGE_WRITE_BIT,
> +                .dstAccessMask = VK_ACCESS_HOST_READ_BIT,
> +                .srcQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED,
> +                .dstQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED,
> +                .buffer = sum_vk->buf,
> +                .size = sum_vk->size,
> +                .offset = 0,
> +            },
> +            .bufferMemoryBarrierCount = 1,
> +        });
> +
> +    RET(ff_vk_exec_submit(vkctx, exec));
> +    ff_vk_exec_wait(vkctx, exec);
> +    if (s->type == UNDETERMINED && det->frame_straight)
> +        s->type = STRAIGHT;
> +
> +    av_buffer_unref(&sum_buf);
> +    return ff_filter_frame(outlink, in);
> +
> +fail:
> +    if (exec)
> +        ff_vk_exec_discard_deps(&s->vkctx, exec);
> +    av_frame_free(&in);
> +    av_buffer_unref(&sum_buf);
> +    return err;
> +}
> +
> +static void alphadetect_vulkan_uninit(AVFilterContext *avctx)
> +{
> +    AlphaDetectVulkanContext *s = avctx->priv;
> +    FFVulkanContext *vkctx = &s->vkctx;
> +
> +    if (s->initialized)
> +        av_log(avctx, AV_LOG_INFO, "Alpha detection: %s\n", type2str(s->type));
> +
> +    ff_vk_exec_pool_free(vkctx, &s->e);
> +    ff_vk_shader_free(vkctx, &s->shd);
> +
> +    av_buffer_pool_uninit(&s->det_buf_pool);
> +
> +    ff_vk_uninit(&s->vkctx);
> +
> +    s->initialized = 0;
> +}
> +
> +static const AVOption alphadetect_vulkan_options[] = {
> +    { NULL }
> +};
> +
> +AVFILTER_DEFINE_CLASS(alphadetect_vulkan);
> +
> +static const AVFilterPad alphadetect_vulkan_inputs[] = {
> +    {
> +        .name         = "default",
> +        .type         = AVMEDIA_TYPE_VIDEO,
> +        .filter_frame = &alphadetect_vulkan_filter_frame,
> +        .config_props = &ff_vk_filter_config_input,
> +    },
> +};
> +
> +static const AVFilterPad alphadetect_vulkan_outputs[] = {
> +    {
> +        .name = "default",
> +        .type = AVMEDIA_TYPE_VIDEO,
> +        .config_props = &ff_vk_filter_config_output,
> +    },
> +};
> +
> +const FFFilter ff_vf_alphadetect_vulkan = {
> +    .p.name         = "alphadetect_vulkan",
> +    .p.description  = NULL_IF_CONFIG_SMALL("Detects if input is premultiplied or straight alpha."),
> +    .p.priv_class   = &alphadetect_vulkan_class,
> +    .p.flags        = AVFILTER_FLAG_HWDEVICE,
> +    .priv_size      = sizeof(AlphaDetectVulkanContext),
> +    .init           = &ff_vk_filter_init,
> +    .uninit         = &alphadetect_vulkan_uninit,
> +    FILTER_INPUTS(alphadetect_vulkan_inputs),
> +    FILTER_OUTPUTS(alphadetect_vulkan_outputs),
> +    FILTER_SINGLE_PIXFMT(AV_PIX_FMT_VULKAN),
> +    .flags_internal = FF_FILTER_FLAG_HWFRAME_AWARE,
> +};
> --
> 2.49.0
>
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