[FFmpeg-devel] [PATCH] Add alphaextract, alphamerge filters

Stefano Sabatini stefasab at gmail.com
Thu Jul 19 09:56:21 CEST 2012


On date Sunday 2012-07-15 11:35:03 -0700, Steven Robertson encoded:
> On Sat, Jul 14, 2012 at 4:03 PM, Nicolas George
[...]
> --- /dev/null
> +++ b/libavfilter/vf_alphaextract.c
[...]
> +static int config_input(AVFilterLink *link)

nit: inlink

> +{
> +    AlphaExtractContext *extract = link->dst->priv;
> +    extract->is_packed_rgb =
> +        ff_fill_rgba_map(extract->rgba_map, link->format) >= 0;
> +    return 0;
> +}
> +
> +static void draw_slice(AVFilterLink *link, int y0, int h, int slice_dir)

nit: inlink

> +{
> +    AlphaExtractContext *extract = link->dst->priv;
> +    AVFilterBufferRef *cur_buf = link->cur_buf;
> +    AVFilterBufferRef *out_buf = link->dst->outputs[0]->out_buf;
> +
> +    if (extract->is_packed_rgb) {
> +        int x, y;
> +        uint8_t *pin, *pout;
> +        for (y = y0; y < (y0 + h); y++) {
> +            pin = cur_buf->data[0] + y * cur_buf->linesize[0] + extract->rgba_map[A];
> +            pout = out_buf->data[0] + y * out_buf->linesize[0];
> +            for (x = 0; x < out_buf->video->w; x++) {
> +                *pout = *pin;
> +                pout += 1;
> +                pin += 4;
> +            }
> +        }

> +    } else {
> +        const int linesize = cur_buf->linesize[A];
> +        av_assert0(linesize == out_buf->linesize[Y]);

I'm not sure this is always correct, indeed I never assume it is in
the code. For example I guess the following may fail:

testsrc,pad=2*iw:2*iw,alphaextract

You could do:
else if (cur_buf->linesize[A] == out_buf->linesize[Y]) {
     memmove
} else {
     copy line by line
}
     
> +
> +        memmove(out_buf->data[Y] + y0 * linesize,
> +                cur_buf->data[A] + y0 * linesize,
> +                linesize * h);
> +    }
> +    ff_draw_slice(link->dst->outputs[0], y0, h, slice_dir);
> +}
> +
> +AVFilter avfilter_vf_alphaextract = {
> +    .name           = "alphaextract",
> +    .description    = NULL_IF_CONFIG_SMALL("Extract an alpha channel as a "
> +                      "grayscale image component."),
> +    .priv_size      = sizeof(AlphaExtractContext),
> +    .query_formats  = query_formats,
> +
> +    .inputs    = (const AVFilterPad[]) {
> +        { .name             = "default",
> +          .type             = AVMEDIA_TYPE_VIDEO,
> +          .config_props     = config_input,
> +          .draw_slice       = draw_slice,
> +          .min_perms        = AV_PERM_READ },
> +        { .name = NULL }
> +    },
> +    .outputs   = (const AVFilterPad[]) {
> +      { .name               = "default",
> +        .type               = AVMEDIA_TYPE_VIDEO, },
> +      { .name = NULL }
> +    },
> +};
> diff --git a/libavfilter/vf_alphamerge.c b/libavfilter/vf_alphamerge.c
> new file mode 100644
> index 0000000..dc5f1c9
> --- /dev/null
> +++ b/libavfilter/vf_alphamerge.c
> @@ -0,0 +1,203 @@
> +/*
> + * Copyright (c) 2012 Steven Robertson
> + *
> + * 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
> + */
> +
> +/**
> + * @file
> + * copy an alpha component from another video's luma
> + */
> +
> +#include <string.h>
> +
> +#include "libavutil/pixfmt.h"
> +#include "avfilter.h"
> +#include "bufferqueue.h"
> +#include "drawutils.h"
> +#include "formats.h"
> +#include "internal.h"
> +#include "video.h"
> +
> +enum { Y, U, V, A };
> +
> +typedef struct {
> +    int frame_requested;
> +    int is_packed_rgb;
> +    uint8_t rgba_map[4];
> +    struct FFBufQueue queue_main;
> +    struct FFBufQueue queue_alpha;
> +} AlphaMergeContext;
> +
> +static av_cold void uninit(AVFilterContext *ctx)
> +{
> +    AlphaMergeContext *merge = ctx->priv;
> +    ff_bufqueue_discard_all(&merge->queue_main);
> +    ff_bufqueue_discard_all(&merge->queue_alpha);
> +}
> +
> +static int query_formats(AVFilterContext *ctx)
> +{
> +    enum PixelFormat main_fmts[] = {
> +        PIX_FMT_YUVA444P, PIX_FMT_YUVA422P, PIX_FMT_YUVA420P,
> +        PIX_FMT_RGBA, PIX_FMT_BGRA, PIX_FMT_ARGB, PIX_FMT_ABGR,
> +        PIX_FMT_NONE
> +    };
> +    enum PixelFormat alpha_fmts[] = { PIX_FMT_GRAY8, PIX_FMT_NONE };
> +    AVFilterFormats *main_formats = ff_make_format_list(main_fmts);
> +    AVFilterFormats *alpha_formats = ff_make_format_list(alpha_fmts);
> +    ff_formats_ref(main_formats, &ctx->inputs[0]->out_formats);
> +    ff_formats_ref(alpha_formats, &ctx->inputs[1]->out_formats);
> +    ff_formats_ref(main_formats, &ctx->outputs[0]->in_formats);
> +    return 0;
> +}
> +
> +static int config_input_main(AVFilterLink *inlink)
> +{
> +    AlphaMergeContext *merge = inlink->dst->priv;
> +    merge->is_packed_rgb =
> +        ff_fill_rgba_map(merge->rgba_map, inlink->format) >= 0;
> +    return 0;
> +}
> +
> +static int config_output(AVFilterLink *outlink)
> +{
> +    AVFilterLink *mainlink = outlink->src->inputs[0];
> +    AVFilterLink *alphalink = outlink->src->inputs[1];

> +    if (mainlink->w != alphalink->w || mainlink->h != alphalink->h)
> +      return AVERROR(EINVAL);

Weird indent, also tell the poor user what's going wrong.

> +
> +    outlink->w = mainlink->w;
> +    outlink->h = mainlink->h;
> +    outlink->time_base = mainlink->time_base;
> +    outlink->sample_aspect_ratio = mainlink->sample_aspect_ratio;
> +    outlink->frame_rate = mainlink->frame_rate;
> +    return 0;
> +}
> +
> +static void start_frame(AVFilterLink *inlink, AVFilterBufferRef *picref) {}
> +static void draw_slice(AVFilterLink *inlink, int y, int h, int slice_dir) {}
> +
> +static void draw_frame(AVFilterContext *ctx,
> +                       AVFilterBufferRef *main_buf,
> +                       AVFilterBufferRef *alpha_buf)
> +{
> +    AlphaMergeContext *merge = ctx->priv;
> +    int h = main_buf->video->h;
> +
> +    if (merge->is_packed_rgb) {
> +        int x, y;
> +        uint8_t *pin, *pout;
> +        for (y = 0; y < h; y++) {
> +            pin = alpha_buf->data[0] + y * alpha_buf->linesize[0];
> +            pout = main_buf->data[0] + y * main_buf->linesize[0] + merge->rgba_map[A];
> +            for (x = 0; x < main_buf->video->w; x++) {
> +                *pout = *pin;
> +                pin += 1;
> +                pout += 4;
> +            }
> +        }
> +    } else {
> +        int y;

> +        int main_line = main_buf->linesize[A];
> +        int alpha_line = alpha_buf->linesize[Y];

nit: *_linesize, "line" has a pretty different meaning (denotes a
buffer rather than a size). Also maybe "const int" can help the
compiler to optimize.

> +
> +        for (y = 0; y < h && y < alpha_buf->video->h; y++) {
> +            memmove(main_buf->data[A] + y * main_line,
> +                    alpha_buf->data[Y] + y * alpha_line,
> +                    FFMIN(main_line, alpha_line));

Any special reason to use memmove rather than memcpy? Can the two
arrays overlap?

Also why are you copying the entire line, rather than just the image
data?

[...]
> +AVFilter avfilter_vf_alphamerge = {
> +    .name           = "alphamerge",

> +    .description    = NULL_IF_CONFIG_SMALL("Copy the luma value of grayscale "
> +                      "frames into the alpha channel of another video."),

Maybe more clear (although a bit longer):
"Copy the luma value of the second input into the alpha channel of the first input."

[...]
> diff --git a/tests/lavfi-regression.sh b/tests/lavfi-regression.sh
> index dd5e2da..224fc8f 100755
> --- a/tests/lavfi-regression.sh
> +++ b/tests/lavfi-regression.sh
> @@ -13,21 +13,25 @@ eval do_$test=y
>  
>  do_video_filter() {
>      label=$1
> -    filters=$2
> +    filters="$2"
>      shift 2
>      printf '%-20s' $label
>      run_avconv $DEC_OPTS -f image2 -vcodec pgmyuv -i $raw_src    \
>          $ENC_OPTS -vf "$filters" -vcodec rawvideo $* -f nut md5:
>  }
>  
> -do_lavfi() {
> -    vfilters="slicify=random,$2"
> +do_lavfi_plain() {
> +    vfilters="$2"
>  
>      if [ $test = $1 ] ; then
>          do_video_filter $test "$vfilters"
>      fi
>  }
>  
> +do_lavfi() {
> +    do_lavfi_plain $1 "slicify=random,$2"
> +}
> +
>  do_lavfi_colormatrix() {
>      do_lavfi "${1}1" "$1=$4:$5,$1=$5:$3,$1=$3:$4,$1=$4:$3,$1=$3:$5,$1=$5:$2"
>      do_lavfi "${1}2" "$1=$2:$3,$1=$3:$2,$1=$2:$4,$1=$4:$2,$1=$2:$5,$1=$5:$4"
> @@ -60,6 +64,11 @@ do_lavfi "vflip"              "vflip"
>  do_lavfi "vflip_crop"         "vflip,crop=iw-100:ih-100:100:100"
>  do_lavfi "vflip_vflip"        "vflip,vflip"
>  

> +do_lavfi_plain "alphamerge_rgb"     "[in]slicify=random,format=bgra,split[o1][o2];[o1][o2]alphamerge[out]"

Here and below, the syntax can be simplified to:
[in]slicify=random,format=bgra,split,alphamerge[out]

which looks less noisy and thus more readable to me.

According to docs (filtergraph syntax, filters.texi):
|If an output pad is not labelled, it is linked by default to the first
|unlabelled input pad of the next filter in the filterchain.

> +do_lavfi_plain "alphamerge_yuv"     "[in]slicify=random,format=yuv420p,split[o1][o2];[o1][o2]alphamerge[out]"
> +do_lavfi_plain "alphaextract_rgb"   "[in]slicify=random,format=bgra,split[o1][o2];[o1][o2]alphamerge,slicify=random,split[o3][o4];[o4]alphaextract[alpha];[o3][alpha]alphamerge[out]"
> +do_lavfi_plain "alphaextract_yuv"   "[in]slicify=random,format=yuv420p,split[o1][o2];[o1][o2]alphamerge,slicify=random,split[o3][o4];[o4]alphaextract[alpha];[o3][alpha]alphamerge[out]"
> +

[...]

Should be good otherwise.
-- 
FFmpeg = Funny and Fierce Multimedia Prodigious Educated Gospel


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