vf_drawtext: Add pkt_pos, pkt_duration, pkt_size as variables

Changes to vf_drawtext.c written by
Calvin Walton <calvin.walton@kepstin.ca>

Changes to filters.texi written by
greg Luce <electron.rotoscope@gmail.com>
with lots of help from Moritz Barsnick and Gyan

Fixes #7947.

doc/filters.texi

@@ -9002,6 +9002,17 @@ to each other, so you can for example specify @code{y=x/dar}.
 
 @item pict_type
 A one character description of the current frame's picture type.
+
+@item pkt_pos
+The current packet's position in the input file or stream
+(in bytes, from the start of the input). A value of -1 indicates
+this info is not available.
+
+@item pkt_duration
+The current packet's duration, in seconds.
+
+@item pkt_size
+The current packet's size (in bytes).
 @end table
 
 @anchor{drawtext_expansion}

libavfilter/version.h

@@ -31,7 +31,8 @@
 
 #define LIBAVFILTER_VERSION_MAJOR   7
 #define LIBAVFILTER_VERSION_MINOR  56
-#define LIBAVFILTER_VERSION_MICRO 100
+#define LIBAVFILTER_VERSION_MICRO 101
+
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \
                                                LIBAVFILTER_VERSION_MINOR, \

libavfilter/vf_drawtext.c

@@ -88,6 +88,9 @@ static const char *const var_names[] = {
     "x",
     "y",
     "pict_type",
+    "pkt_pos",
+    "pkt_duration",
+    "pkt_size",
     NULL
 };
 
@@ -125,6 +128,9 @@ enum var_name {
     VAR_X,
     VAR_Y,
     VAR_PICT_TYPE,
+    VAR_PKT_POS,
+    VAR_PKT_DURATION,
+    VAR_PKT_SIZE,
     VAR_VARS_NB
 };
 
@@ -1516,6 +1522,9 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
         NAN : frame->pts * av_q2d(inlink->time_base);
 
     s->var_values[VAR_PICT_TYPE] = frame->pict_type;
+    s->var_values[VAR_PKT_POS] = frame->pkt_pos;
+    s->var_values[VAR_PKT_DURATION] = frame->pkt_duration * av_q2d(inlink->time_base);
+    s->var_values[VAR_PKT_SIZE] = frame->pkt_size;
     s->metadata = frame->metadata;
 
     draw_text(ctx, frame, frame->width, frame->height);