lavfi: Add fps filter.

Partially based on a patch by Robert Nagy <ronag89@gmail.com>

Changelog

@@ -18,6 +18,7 @@ version <next>:
 - drop support for avconv without libavfilter
 - add libavresample audio conversion library
 - audio filters support in libavfilter and avconv
+- add fps filter
 
 
 version 0.8:

doc/filters.texi

@@ -814,6 +814,19 @@ format=yuv420p
 format=yuv420p:yuv444p:yuv410p
 @end example
 
+@section fps
+
+Convert the video to specified constant framerate by duplicating or dropping
+frames as necessary.
+
+This filter accepts the following named parameters:
+@table @option
+
+@item fps
+Desired output framerate.
+
+@end table
+
 @anchor{frei0r}
 @section frei0r
 

libavfilter/Makefile

@@ -46,6 +46,7 @@ OBJS-$(CONFIG_FADE_FILTER)                   += vf_fade.o
 OBJS-$(CONFIG_FIELDORDER_FILTER)             += vf_fieldorder.o
 OBJS-$(CONFIG_FIFO_FILTER)                   += vf_fifo.o
 OBJS-$(CONFIG_FORMAT_FILTER)                 += vf_format.o
+OBJS-$(CONFIG_FPS_FILTER)                    += vf_fps.o
 OBJS-$(CONFIG_FREI0R_FILTER)                 += vf_frei0r.o
 OBJS-$(CONFIG_GRADFUN_FILTER)                += vf_gradfun.o
 OBJS-$(CONFIG_HFLIP_FILTER)                  += vf_hflip.o

libavfilter/allfilters.c

@@ -55,6 +55,7 @@ void avfilter_register_all(void)
     REGISTER_FILTER (FIELDORDER,  fieldorder,  vf);
     REGISTER_FILTER (FIFO,        fifo,        vf);
     REGISTER_FILTER (FORMAT,      format,      vf);
+    REGISTER_FILTER (FPS,         fps,         vf);
     REGISTER_FILTER (FREI0R,      frei0r,      vf);
     REGISTER_FILTER (GRADFUN,     gradfun,     vf);
     REGISTER_FILTER (HFLIP,       hflip,       vf);

libavfilter/version.h

@@ -29,7 +29,7 @@
 #include "libavutil/avutil.h"
 
 #define LIBAVFILTER_VERSION_MAJOR  2
-#define LIBAVFILTER_VERSION_MINOR  17
+#define LIBAVFILTER_VERSION_MINOR  18
 #define LIBAVFILTER_VERSION_MICRO  0
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \

libavfilter/vf_fps.c

@@ -0,0 +1,271 @@
+/*
+ * This file is part of Libav.
+ *
+ * Libav 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.
+ *
+ * Libav 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 Libav; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file
+ * a filter enforcing given constant framerate
+ */
+
+#include "libavutil/fifo.h"
+#include "libavutil/mathematics.h"
+#include "libavutil/opt.h"
+#include "libavutil/parseutils.h"
+
+#include "avfilter.h"
+
+typedef struct FPSContext {
+    const AVClass *class;
+
+    AVFifoBuffer *fifo;     ///< store frames until we get two successive timestamps
+
+    /* timestamps in input timebase */
+    int64_t first_pts;      ///< pts of the first frame that arrived on this filter
+    int64_t pts;            ///< pts of the first frame currently in the fifo
+
+    AVRational framerate;   ///< target framerate
+    char *fps;              ///< a string describing target framerate
+
+    /* statistics */
+    int frames_in;             ///< number of frames on input
+    int frames_out;            ///< number of frames on output
+    int dup;                   ///< number of frames duplicated
+    int drop;                  ///< number of framed dropped
+} FPSContext;
+
+#define OFFSET(x) offsetof(FPSContext, x)
+#define V AV_OPT_FLAG_VIDEO_PARAM
+static const AVOption options[] = {
+    { "fps", "A string describing desired output framerate", OFFSET(fps), AV_OPT_TYPE_STRING, { .str = "25" }, .flags = V },
+    { NULL },
+};
+
+static const AVClass class = {
+    .class_name = "FPS filter",
+    .item_name  = av_default_item_name,
+    .option     = options,
+    .version    = LIBAVUTIL_VERSION_INT,
+};
+
+static av_cold int init(AVFilterContext *ctx, const char *args, void *opaque)
+{
+    FPSContext *s = ctx->priv;
+    int ret;
+
+    s->class = &class;
+    av_opt_set_defaults(s);
+
+    if ((ret = av_set_options_string(s, args, "=", ":")) < 0) {
+        av_log(ctx, AV_LOG_ERROR, "Error parsing the options string %s.\n",
+               args);
+        return ret;
+    }
+
+    if ((ret = av_parse_video_rate(&s->framerate, s->fps)) < 0) {
+        av_log(ctx, AV_LOG_ERROR, "Error parsing framerate %s.\n", s->fps);
+        return ret;
+    }
+    av_opt_free(s);
+
+    if (!(s->fifo = av_fifo_alloc(2*sizeof(AVFilterBufferRef*))))
+        return AVERROR(ENOMEM);
+
+    av_log(ctx, AV_LOG_VERBOSE, "fps=%d/%d\n", s->framerate.num, s->framerate.den);
+    return 0;
+}
+
+static void flush_fifo(AVFifoBuffer *fifo)
+{
+    while (av_fifo_size(fifo)) {
+        AVFilterBufferRef *tmp;
+        av_fifo_generic_read(fifo, &tmp, sizeof(tmp), NULL);
+        avfilter_unref_buffer(tmp);
+    }
+}
+
+static av_cold void uninit(AVFilterContext *ctx)
+{
+    FPSContext *s = ctx->priv;
+    if (s->fifo) {
+        flush_fifo(s->fifo);
+        av_fifo_free(s->fifo);
+    }
+
+    av_log(ctx, AV_LOG_VERBOSE, "%d frames in, %d frames out; %d frames dropped, "
+           "%d frames duplicated.\n", s->frames_in, s->frames_out, s->drop, s->dup);
+}
+
+static int config_props(AVFilterLink* link)
+{
+    FPSContext   *s = link->src->priv;
+
+    link->time_base = (AVRational){ s->framerate.den, s->framerate.num };
+    link->w         = link->src->inputs[0]->w;
+    link->h         = link->src->inputs[0]->h;
+    s->pts          = AV_NOPTS_VALUE;
+
+    return 0;
+}
+
+static int request_frame(AVFilterLink *outlink)
+{
+    AVFilterContext *ctx = outlink->src;
+    FPSContext        *s = ctx->priv;
+    int frames_out = s->frames_out;
+    int ret = 0;
+
+    while (ret >= 0 && s->frames_out == frames_out)
+        ret = avfilter_request_frame(ctx->inputs[0]);
+
+    /* flush the fifo */
+    if (ret == AVERROR_EOF && av_fifo_size(s->fifo)) {
+        int i;
+        for (i = 0; av_fifo_size(s->fifo); i++) {
+            AVFilterBufferRef *buf;
+
+            av_fifo_generic_read(s->fifo, &buf, sizeof(buf), NULL);
+            buf->pts = av_rescale_q(s->first_pts, ctx->inputs[0]->time_base,
+                                    outlink->time_base) + s->frames_out;
+
+            avfilter_start_frame(outlink, buf);
+            avfilter_draw_slice(outlink, 0, outlink->h, 1);
+            avfilter_end_frame(outlink);
+            s->frames_out++;
+        }
+        return 0;
+    }
+
+    return ret;
+}
+
+static int write_to_fifo(AVFifoBuffer *fifo, AVFilterBufferRef *buf)
+{
+    int ret;
+
+    if (!av_fifo_space(fifo) &&
+        (ret = av_fifo_realloc2(fifo, 2*av_fifo_size(fifo))))
+        return ret;
+
+    av_fifo_generic_write(fifo, &buf, sizeof(buf), NULL);
+    return 0;
+}
+
+static void end_frame(AVFilterLink *inlink)
+{
+    AVFilterContext    *ctx = inlink->dst;
+    FPSContext           *s = ctx->priv;
+    AVFilterLink   *outlink = ctx->outputs[0];
+    AVFilterBufferRef  *buf = inlink->cur_buf;
+    int64_t delta;
+    int i;
+
+    s->frames_in++;
+    /* discard frames until we get the first timestamp */
+    if (s->pts == AV_NOPTS_VALUE) {
+        if (buf->pts != AV_NOPTS_VALUE) {
+            write_to_fifo(s->fifo, buf);
+            s->first_pts = s->pts = buf->pts;
+        } else {
+            av_log(ctx, AV_LOG_WARNING, "Discarding initial frame(s) with no "
+                   "timestamp.\n");
+            avfilter_unref_buffer(buf);
+            s->drop++;
+        }
+        return;
+    }
+
+    /* now wait for the next timestamp */
+    if (buf->pts == AV_NOPTS_VALUE) {
+        write_to_fifo(s->fifo, buf);
+        return;
+    }
+
+    /* number of output frames */
+    delta = av_rescale_q(buf->pts - s->pts, inlink->time_base,
+                         outlink->time_base);
+
+    if (delta < 1) {
+        /* drop the frame and everything buffered except the first */
+        AVFilterBufferRef *tmp;
+        int drop = av_fifo_size(s->fifo)/sizeof(AVFilterBufferRef*);
+
+        av_log(ctx, AV_LOG_DEBUG, "Dropping %d frame(s).\n", drop);
+        s->drop += drop;
+
+        av_fifo_generic_read(s->fifo, &tmp, sizeof(tmp), NULL);
+        flush_fifo(s->fifo);
+        write_to_fifo(s->fifo, tmp);
+
+        avfilter_unref_buffer(buf);
+        return;
+    }
+
+    /* can output >= 1 frames */
+    for (i = 0; i < delta; i++) {
+        AVFilterBufferRef *buf_out;
+        av_fifo_generic_read(s->fifo, &buf_out, sizeof(buf_out), NULL);
+
+        /* duplicate the frame if needed */
+        if (!av_fifo_size(s->fifo) && i < delta - 1) {
+            av_log(ctx, AV_LOG_DEBUG, "Duplicating frame.\n");
+            write_to_fifo(s->fifo, avfilter_ref_buffer(buf_out, AV_PERM_READ));
+            s->dup++;
+        }
+
+        buf_out->pts = av_rescale_q(s->first_pts, inlink->time_base,
+                                    outlink->time_base) + s->frames_out;
+
+        avfilter_start_frame(outlink, buf_out);
+        avfilter_draw_slice(outlink, 0, outlink->h, 1);
+        avfilter_end_frame(outlink);
+        s->frames_out++;
+    }
+    flush_fifo(s->fifo);
+
+    write_to_fifo(s->fifo, buf);
+    s->pts = s->first_pts + av_rescale_q(s->frames_out, outlink->time_base, inlink->time_base);
+}
+
+static void null_start_frame(AVFilterLink *link, AVFilterBufferRef *buf)
+{
+}
+
+static void null_draw_slice(AVFilterLink *link, int y, int h, int slice_dir)
+{
+}
+
+AVFilter avfilter_vf_fps = {
+    .name        = "fps",
+    .description = NULL_IF_CONFIG_SMALL("Force constant framerate"),
+
+    .init      = init,
+    .uninit    = uninit,
+
+    .priv_size = sizeof(FPSContext),
+
+    .inputs    = (AVFilterPad[]) {{ .name            = "default",
+                                    .type            = AVMEDIA_TYPE_VIDEO,
+                                    .start_frame     = null_start_frame,
+                                    .draw_slice      = null_draw_slice,
+                                    .end_frame       = end_frame, },
+                                  { .name = NULL}},
+    .outputs   = (AVFilterPad[]) {{ .name            = "default",
+                                    .type            = AVMEDIA_TYPE_VIDEO,
+                                    .request_frame   = request_frame,
+                                    .config_props    = config_props},
+                                  { .name = NULL}},
+};