vsink_buffer: make the buffer cache all the incoming frames

Allow to cache more than one frame (e.g. for filters which return
more than one frame when avfilter_request_frame() is called on them),
and do not discard previously cached frames when a new one is added.

libavfilter/avfilter.h

@@ -30,7 +30,7 @@
 
 #define LIBAVFILTER_VERSION_MAJOR  2
 #define LIBAVFILTER_VERSION_MINOR 29
-#define LIBAVFILTER_VERSION_MICRO  1
+#define LIBAVFILTER_VERSION_MICRO  2
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \
                                                LIBAVFILTER_VERSION_MINOR, \

libavfilter/vsink_buffer.c

@@ -23,14 +23,17 @@
  * buffer video sink
  */
 
+#include "libavutil/fifo.h"
 #include "avfilter.h"
 #include "vsink_buffer.h"
 
 typedef struct {
-    AVFilterBufferRef *picref;   ///< cached picref
+    AVFifoBuffer *fifo;          ///< FIFO buffer of video frame references
     enum PixelFormat *pix_fmts;  ///< accepted pixel formats, must be terminated with -1
 } BufferSinkContext;
 
+#define FIFO_INIT_SIZE 8
+
 static av_cold int init(AVFilterContext *ctx, const char *args, void *opaque)
 {
     BufferSinkContext *buf = ctx->priv;
@@ -40,6 +43,12 @@ static av_cold int init(AVFilterContext *ctx, const char *args, void *opaque)
         return AVERROR(EINVAL);
     }
 
+    buf->fifo = av_fifo_alloc(FIFO_INIT_SIZE*sizeof(AVFilterBufferRef *));
+    if (!buf->fifo) {
+        av_log(ctx, AV_LOG_ERROR, "Failed to allocate fifo\n");
+        return AVERROR(ENOMEM);
+    }
+
     buf->pix_fmts = opaque;
     return 0;
 }
@@ -47,19 +56,36 @@ static av_cold int init(AVFilterContext *ctx, const char *args, void *opaque)
 static av_cold void uninit(AVFilterContext *ctx)
 {
     BufferSinkContext *buf = ctx->priv;
-
-    if (buf->picref)
-        avfilter_unref_buffer(buf->picref);
-    buf->picref = NULL;
+    AVFilterBufferRef *picref;
+
+    if (buf->fifo) {
+        while (av_fifo_size(buf->fifo) >= sizeof(AVFilterBufferRef *)) {
+            av_fifo_generic_read(buf->fifo, &picref, sizeof(picref), NULL);
+            avfilter_unref_buffer(picref);
+        }
+        av_fifo_free(buf->fifo);
+        buf->fifo = NULL;
+    }
 }
 
 static void end_frame(AVFilterLink *inlink)
 {
+    AVFilterContext *ctx = inlink->dst;
     BufferSinkContext *buf = inlink->dst->priv;
 
-    if (buf->picref)            /* drop the last cached frame */
-        avfilter_unref_buffer(buf->picref);
-    buf->picref = inlink->cur_buf;
+    if (av_fifo_space(buf->fifo) < sizeof(AVFilterBufferRef *)) {
+        /* realloc fifo size */
+        if (av_fifo_realloc2(buf->fifo, av_fifo_size(buf->fifo) * 2) < 0) {
+            av_log(ctx, AV_LOG_ERROR,
+                   "Cannot buffer more frames. Consume some available frames "
+                   "before adding new ones.\n");
+            return;
+        }
+    }
+
+    /* cache frame */
+    av_fifo_generic_write(buf->fifo,
+                          &inlink->cur_buf, sizeof(AVFilterBufferRef *), NULL);
 }
 
 static int query_formats(AVFilterContext *ctx)
@@ -79,17 +105,18 @@ int av_vsink_buffer_get_video_buffer_ref(AVFilterContext *ctx,
     *picref = NULL;
 
     /* no picref available, fetch it from the filterchain */
-    if (!buf->picref) {
+    if (!av_fifo_size(buf->fifo)) {
         if ((ret = avfilter_request_frame(inlink)) < 0)
             return ret;
     }
 
-    if (!buf->picref)
+    if (!av_fifo_size(buf->fifo))
         return AVERROR(EINVAL);
 
-    *picref = buf->picref;
-    if (!(flags & AV_VSINK_BUF_FLAG_PEEK))
-        buf->picref = NULL;
+    if (flags & AV_VSINK_BUF_FLAG_PEEK)
+        *picref = (AVFilterBufferRef *)av_fifo_peek2(buf->fifo, 0);
+    else
+        av_fifo_generic_read(buf->fifo, picref, sizeof(*picref), NULL);
 
     return 0;
 }