[FFmpeg-soc] [PATCH] Add fade filter to libavfilter

Brandon Mintern bmintern at gmail.com
Wed Mar 31 06:43:50 CEST 2010


I am happy to present my first-ever open source code contribution, a
"fade" filter for libavfilter! Here is some example usage:

# Fade in first 30 frames of video
ffmpeg -i input.avi -vfilters fade=in:1:30 output.avi

# Fade out last 45 frames of a 200-frame video
ffmpeg -i input.avi -vfilters fade=out:156:45 output.avi

# Fade in first 25 frames and fade out last 25 frames of a 1000-frame video
ffmpeg -i input.avi -vfilters "fade=in:1:25, fade=out:976:25" output.avi

# Make first 5 frames black, then fade in from frame 6-25
ffmpeg -i input.avi -vfilters "fade=in:6:20" output.avi

That is, the arguments to fade are
"fade=in/out:start_frame:fade_length". The fade_length is simply the
number of frames that the fade occurs over. Any remaining frames after
a fade=out is completed are black, and any frames preceding
start_frame on a fade=in are black. If fade_length is shorter than
total_video_frames - start_frame, then the fade will not be all the
way to/from black before the end of the video.

I am open to changing the API although I rather like the fade=in/out
argument as it is; I think it makes the command line readable. In
particular, the programmer in me feels like counting should begin at
0, but if there's not yet a precedent I think it makes more sense for
a filter to begin counting frames from 1; this is definitely something
I'm unsure about. And I am definitely open to criticism on my code
quality -- I am not expecting anyone to go easy on me. The patch
follows, and it is currently also available at
http://bmintern.homeunix.com/~brandon/vf_fade.patch

Brandon

Index: allfilters.c
===================================================================
--- allfilters.c	(revision 5726)
+++ allfilters.c	(working copy)
@@ -37,6 +37,7 @@
     REGISTER_FILTER (ASPECT,      aspect,      vf);
     REGISTER_FILTER (CROP,        crop,        vf);
     REGISTER_FILTER (DRAWBOX,     drawbox,     vf);
+    REGISTER_FILTER (FADE,        fade,        vf);
     REGISTER_FILTER (FIFO,        fifo,        vf);
     REGISTER_FILTER (FORMAT,      format,      vf);
     REGISTER_FILTER (FPS,         fps,         vf);
Index: vf_fade.c
===================================================================
--- vf_fade.c	(revision 0)
+++ vf_fade.c	(revision 0)
@@ -0,0 +1,169 @@
+/*
+ * video fade filter
+ * copyright (c) 2010 Brandon Mintern
+ * based heavily on vf_negate.c which is copyright (c) 2007 Bobby Bingham
+ *
+ * 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
+ */
+
+/*
+ # A few usage examples follow, usable too as test scenarios.
+
+ # Fade in first 30 frames of video
+ ffmpeg -i input.avi -vfilters fade=in:1:30 output.avi
+
+ # Fade out last 45 frames of a 200-frame video
+ ffmpeg -i input.avi -vfilters fade=out:156:45 output.avi
+
+ # Fade in first 25 frames and fade out last 25 frames of a 1000-frame video
+ ffmpeg -i input.avi -vfilters "fade=in:1:25, fade=out:976:25" output.avi
+
+ # Make first 5 frames black, then fade in from frame 6-25
+ ffmpeg -i input.avi -vfilters "fade=in:6:20" output.avi
+*/
+
+#include "avfilter.h"
+
+typedef struct
+{
+    float fade_factor, fade_per_frame;
+    unsigned int frame_index, start_frame, stop_frame;
+    int hsub, vsub;
+} FadeContext;
+
+static av_cold int init(AVFilterContext *ctx, const char *args, void *opaque)
+{
+    FadeContext *fade = ctx->priv;
+    unsigned int frames;
+    char in_out[4];
+
+    if(args && sscanf(args, " %3[^:]:%u:%u", in_out,
+                   &fade->start_frame, &frames) == 3) {
+        frames = frames ? frames : 1;
+        fade->fade_per_frame = 1.0 / frames;
+        if (!strcmp(in_out, "in"))
+            fade->fade_factor = 0.0;
+        else if (!strcmp(in_out, "out")) {
+            fade->fade_per_frame = -fade->fade_per_frame;
+            fade->fade_factor = 1.0;
+        }
+        else {
+            av_log(ctx, AV_LOG_ERROR,
+                "init() 1st arg must be 'in' or 'out':'%s'\n", in_out);
+            return -1;
+        }
+
+        fade->frame_index = 1;
+        fade->start_frame = fade->start_frame ? fade->start_frame : 1;
+        fade->stop_frame = fade->start_frame + frames;
+        return 0;
+    }
+    av_log(ctx, AV_LOG_ERROR,
+           "init() expected 3 arguments '(in|out):#:#':'%s'\n", args);
+    return -1;
+}
+
+static int query_formats(AVFilterContext *ctx)
+{
+    enum PixelFormat pix_fmts[] = {
+        PIX_FMT_YUV444P,  PIX_FMT_YUV422P,  PIX_FMT_YUV420P,
+        PIX_FMT_YUV411P,  PIX_FMT_YUV410P,
+        PIX_FMT_YUVJ444P, PIX_FMT_YUVJ422P, PIX_FMT_YUVJ420P,
+        PIX_FMT_YUV440P,  PIX_FMT_YUVJ440P,
+        PIX_FMT_NONE
+    };
+
+    avfilter_set_common_formats(ctx, avfilter_make_format_list(pix_fmts));
+    return 0;
+}
+
+static int config_props(AVFilterLink *link)
+{
+    FadeContext *fade = link->dst->priv;
+    avcodec_get_chroma_sub_sample(link->format, &fade->hsub, &fade->vsub);
+    return 0;
+}
+
+
+static void start_frame(AVFilterLink *link, AVFilterPicRef *picref)
+{
+    FadeContext *fade = link->dst->priv;
+    if(fade->frame_index >= fade->start_frame &&
+       fade->frame_index < fade->stop_frame) {
+        fade->fade_factor += fade->fade_per_frame;
+    }
+    fade->frame_index++;
+    avfilter_default_start_frame(link, picref);
+}
+
+static void draw_slice(AVFilterLink *link, int y, int h, int slice_dir)
+{
+    FadeContext *fade = link->dst->priv;
+    AVFilterPicRef *in  = link->cur_pic;
+    AVFilterPicRef *out = link->dst->outputs[0]->outpic;
+    uint8_t *inrow, *outrow;
+    int i, j, plane;
+
+    /* luma plane */
+    inrow  = in-> data[0] + y * in-> linesize[0];
+    outrow = out->data[0] + y * out->linesize[0];
+    for(i = 0; i < h; i ++) {
+        for(j = 0; j < link->w; j ++)
+            outrow[j] = (uint8_t) ((float) inrow[j] * fade->fade_factor + 0.5);
+        inrow  += in-> linesize[0];
+        outrow += out->linesize[0];
+    }
+
+    /* chroma planes */
+    for(plane = 1; plane < 3; plane ++) {
+        inrow  = in-> data[plane] + (y >> fade->vsub) * in-> linesize[plane];
+        outrow = out->data[plane] + (y >> fade->vsub) * out->linesize[plane];
+
+        for(i = 0; i < h >> fade->vsub; i ++) {
+            for(j = 0; j < link->w >> fade->hsub; j ++) {
+                outrow[j] = 128 + (int) ((inrow[j]-128) *
fade->fade_factor + 0.5);
+            }
+            inrow  += in-> linesize[plane];
+            outrow += out->linesize[plane];
+        }
+    }
+
+    avfilter_draw_slice(link->dst->outputs[0], y, h, slice_dir);
+}
+
+AVFilter avfilter_vf_fade =
+{
+    .name      = "fade",
+
+    .init      = init,
+
+    .priv_size = sizeof(FadeContext),
+
+    .query_formats = query_formats,
+
+    .inputs    = (AVFilterPad[]) {{ .name            = "default",
+                                    .type            = CODEC_TYPE_VIDEO,
+                                    .start_frame     = start_frame,
+                                    .draw_slice      = draw_slice,
+                                    .config_props    = config_props,
+                                    .min_perms       = AV_PERM_READ, },
+                                  { .name = NULL}},
+    .outputs   = (AVFilterPad[]) {{ .name            = "default",
+                                    .type            = CODEC_TYPE_VIDEO, },
+                                  { .name = NULL}},
+};
+
Index: Makefile
===================================================================
--- Makefile	(revision 5726)
+++ Makefile	(working copy)
@@ -18,6 +18,7 @@
 OBJS-$(CONFIG_ASPECT_FILTER)                 += vf_aspect.o
 OBJS-$(CONFIG_CROP_FILTER)                   += vf_crop.o
 OBJS-$(CONFIG_DRAWBOX_FILTER)                += vf_drawbox.o
+OBJS-$(CONFIG_FADE_FILTER)                   += vf_fade.o
 OBJS-$(CONFIG_FIFO_FILTER)                   += vf_fifo.o
 OBJS-$(CONFIG_FORMAT_FILTER)                 += vf_format.o
 OBJS-$(CONFIG_FPS_FILTER)                    += vf_fps.o


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