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diff --git a/libavfilter/filters.h b/libavfilter/filters.h
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+/*
+ * Filters implementation helper functions
+ *
+ * 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
+ */
+
+#ifndef AVFILTER_FILTERS_H
+#define AVFILTER_FILTERS_H
+
+/**
+ * Filters implementation helper functions
+ */
+
+#include "avfilter.h"
+#include "internal.h"
+
+/**
+ * Special return code when activate() did not do anything.
+ */
+#define FFERROR_NOT_READY FFERRTAG('N','R','D','Y')
+
+/**
+ * Mark a filter ready and schedule it for activation.
+ *
+ * This is automatically done when something happens to the filter (queued
+ * frame, status change, request on output).
+ * Filters implementing the activate callback can call it directly to
+ * perform one more round of processing later.
+ * It is also useful for filters reacting to external or asynchronous
+ * events.
+ */
+void ff_filter_set_ready(AVFilterContext *filter, unsigned priority);
+
+/**
+ * Process the commands queued in the link up to the time of the frame.
+ * Commands will trigger the process_command() callback.
+ * @return  >= 0 or AVERROR code.
+ */
+int ff_inlink_process_commands(AVFilterLink *link, const AVFrame *frame);
+
+/**
+ * Evaluate the timeline expression of the link for the time and properties
+ * of the frame.
+ * @return  >0 if enabled, 0 if disabled
+ * @note  It does not update link->dst->is_disabled.
+ */
+int ff_inlink_evaluate_timeline_at_frame(AVFilterLink *link, const AVFrame *frame);
+
+/**
+ * Test if a frame is available on the link.
+ * @return  >0 if a frame is available
+ */
+int ff_inlink_check_available_frame(AVFilterLink *link);
+
+/**
+ * Test if enough samples are available on the link.
+ * @return  >0 if enough samples are available
+ * @note  on EOF and error, min becomes 1
+ */
+int ff_inlink_check_available_samples(AVFilterLink *link, unsigned min);
+
+/**
+ * Take a frame from the link's FIFO and update the link's stats.
+ *
+ * If ff_inlink_check_available_frame() was previously called, the
+ * preferred way of expressing it is "av_assert1(ret);" immediately after
+ * ff_inlink_consume_frame(). Negative error codes must still be checked.
+ *
+ * @note  May trigger process_command() and/or update is_disabled.
+ * @return  >0 if a frame is available,
+ *          0 and set rframe to NULL if no frame available,
+ *          or AVERROR code
+ */
+int ff_inlink_consume_frame(AVFilterLink *link, AVFrame **rframe);
+
+/**
+ * Take samples from the link's FIFO and update the link's stats.
+ *
+ * If ff_inlink_check_available_samples() was previously called, the
+ * preferred way of expressing it is "av_assert1(ret);" immediately after
+ * ff_inlink_consume_samples(). Negative error codes must still be checked.
+ *
+ * @note  May trigger process_command() and/or update is_disabled.
+ * @return  >0 if a frame is available,
+ *          0 and set rframe to NULL if no frame available,
+ *          or AVERROR code
+ */
+int ff_inlink_consume_samples(AVFilterLink *link, unsigned min, unsigned max,
+                            AVFrame **rframe);
+
+/**
+ * Make sure a frame is writable.
+ * This is similar to av_frame_make_writable() except it uses the link's
+ * buffer allocation callback, and therefore allows direct rendering.
+ */
+int ff_inlink_make_frame_writable(AVFilterLink *link, AVFrame **rframe);
+
+/**
+ * Test and acknowledge the change of status on the link.
+ *
+ * Status means EOF or an error condition; a change from the normal (0)
+ * status to a non-zero status can be queued in a filter's input link, it
+ * becomes relevant after the frames queued in the link's FIFO are
+ * processed. This function tests if frames are still queued and if a queued
+ * status change has not yet been processed. In that case it performs basic
+ * treatment (updating the link's timestamp) and returns a positive value to
+ * let the filter do its own treatments (flushing...).
+ *
+ * Filters implementing the activate callback should call this function when
+ * they think it might succeed (usually after checking unsuccessfully for a
+ * queued frame).
+ * Filters implementing the filter_frame and request_frame callbacks do not
+ * need to call that since the same treatment happens in ff_filter_frame().
+ *
+ * @param[out] rstatus  new or current status
+ * @param[out] rpts     current timestamp of the link in link time base
+ * @return  >0 if status changed, <0 if status already acked, 0 otherwise
+ */
+int ff_inlink_acknowledge_status(AVFilterLink *link, int *rstatus, int64_t *rpts);
+
+/**
+ * Mark that a frame is wanted on the link.
+ * Unlike ff_filter_frame(), it must not be called when the link has a
+ * non-zero status, and thus does not acknowledge it.
+ * Also it cannot fail.
+ */
+void ff_inlink_request_frame(AVFilterLink *link);
+
+/**
+ * Set the status on an input link.
+ * Also discard all frames in the link's FIFO.
+ */
+void ff_inlink_set_status(AVFilterLink *link, int status);
+
+/**
+ * Test if a frame is wanted on an output link.
+ */
+static inline int ff_outlink_frame_wanted(AVFilterLink *link)
+{
+    return link->frame_wanted_out;
+}
+
+/**
+ * Get the status on an output link.
+ */
+int ff_outlink_get_status(AVFilterLink *link);
+
+/**
+ * Set the status field of a link from the source filter.
+ * The pts should reflect the timestamp of the status change,
+ * in link time base and relative to the frames timeline.
+ * In particular, for AVERROR_EOF, it should reflect the
+ * end time of the last frame.
+ */
+static inline void ff_outlink_set_status(AVFilterLink *link, int status, int64_t pts)
+{
+    ff_avfilter_link_set_in_status(link, status, pts);
+}
+
+/**
+ * Forward the status on an output link to an input link.
+ * If the status is set, it will discard all queued frames and this macro
+ * will return immediately.
+ */
+#define FF_FILTER_FORWARD_STATUS_BACK(outlink, inlink) do { \
+    int ret = ff_outlink_get_status(outlink); \
+    if (ret) { \
+        ff_inlink_set_status(inlink, ret); \
+        return 0; \
+    } \
+} while (0)
+
+/**
+ * Forward the status on an output link to all input links.
+ * If the status is set, it will discard all queued frames and this macro
+ * will return immediately.
+ */
+#define FF_FILTER_FORWARD_STATUS_BACK_ALL(outlink, filter) do { \
+    int ret = ff_outlink_get_status(outlink); \
+    if (ret) { \
+        unsigned i; \
+        for (i = 0; i < filter->nb_inputs; i++) \
+            ff_inlink_set_status(filter->inputs[i], ret); \
+        return 0; \
+    } \
+} while (0)
+
+/**
+ * Acknowledge the status on an input link and forward it to an output link.
+ * If the status is set, this macro will return immediately.
+ */
+#define FF_FILTER_FORWARD_STATUS(inlink, outlink) do { \
+    int status; \
+    int64_t pts; \
+    if (ff_inlink_acknowledge_status(inlink, &status, &pts)) { \
+        ff_outlink_set_status(outlink, status, pts); \
+        return 0; \
+    } \
+} while (0)
+
+/**
+ * Acknowledge the status on an input link and forward it to an output link.
+ * If the status is set, this macro will return immediately.
+ */
+#define FF_FILTER_FORWARD_STATUS_ALL(inlink, filter) do { \
+    int status; \
+    int64_t pts; \
+    if (ff_inlink_acknowledge_status(inlink, &status, &pts)) { \
+        unsigned i; \
+        for (i = 0; i < filter->nb_outputs; i++) \
+            ff_outlink_set_status(filter->outputs[i], status, pts); \
+        return 0; \
+    } \
+} while (0)
+
+/**
+ * Forward the frame_wanted_out flag from an output link to an input link.
+ * If the flag is set, this macro will return immediately.
+ */
+#define FF_FILTER_FORWARD_WANTED(outlink, inlink) do { \
+    if (ff_outlink_frame_wanted(outlink)) { \
+        ff_inlink_request_frame(inlink); \
+        return 0; \
+    } \
+} while (0)
+
+#endif /* AVFILTER_FILTERS_H */