Manually set avg_frame_rate on stream copy.

av/av.ml

@@ -139,6 +139,13 @@ let mk_stream container index = { container; index; decoder = None }
 external get_codec_params : (_, 'm, _) stream -> 'm Avcodec.params
   = "ocaml_av_get_stream_codec_parameters"
 
+external get_avg_frame_rate : (_, video, _) stream -> Avutil.rational option
+  = "ocaml_av_get_stream_avg_frame_rate"
+
+external set_avg_frame_rate :
+  (_, video, _) stream -> Avutil.rational option -> unit
+  = "ocaml_av_set_stream_avg_frame_rate"
+
 external get_time_base : (_, _, _) stream -> Avutil.rational
   = "ocaml_av_get_stream_time_base"
 

av/av.mli

@@ -127,6 +127,12 @@ val get_index : (_, _, _) stream -> int
     codec allocation failed. *)
 val get_codec_params : (_, 'media, _) stream -> 'media Avcodec.params
 
+(** [get_avg_frame_rate stream] returns the average frame rate, if set. *)
+val get_avg_frame_rate : (_, video, _) stream -> Avutil.rational option
+
+(** [set_avg_frame_rate stream rate] sets the average frame rate, if set. *)
+val set_avg_frame_rate : (_, video, _) stream -> Avutil.rational option -> unit
+
 (** [Av.get_time_base stream] return the time base of the [stream]. *)
 val get_time_base : (_, _, _) stream -> Avutil.rational
 

av/av_stubs.c

@@ -22,8 +22,8 @@
 #include <libavutil/audio_fifo.h>
 #include <libavutil/avstring.h>
 #include <libavutil/opt.h>
-#include <libavutil/timestamp.h>
 #include <libavutil/parseutils.h>
+#include <libavutil/timestamp.h>
 
 #include "av_stubs.h"
 #include "avcodec_stubs.h"
@@ -196,6 +196,42 @@ CAMLprim value ocaml_av_get_stream_codec_parameters(value _stream) {
   CAMLreturn(ans);
 }
 
+CAMLprim value ocaml_av_get_stream_avg_frame_rate(value _stream) {
+  CAMLparam1(_stream);
+  CAMLlocal3(ans, ret, _av);
+  _av = Field(_stream, 0);
+  av_t *av = Av_val(_av);
+  int index = StreamIndex_val(_stream);
+  AVStream *st = av->format_context->streams[index];
+
+  if (!st->avg_frame_rate.num)
+    CAMLreturn(Val_none);
+
+  value_of_rational(&av->format_context->streams[index]->avg_frame_rate, &ans);
+
+  ret = caml_alloc_tuple(1);
+  Store_field(ret, 0, ans);
+
+  CAMLreturn(ret);
+}
+
+CAMLprim value ocaml_av_set_stream_avg_frame_rate(value _stream,
+                                                  value _avg_frame_rate) {
+  CAMLparam2(_stream, _avg_frame_rate);
+  CAMLlocal1(_av);
+  _av = Field(_stream, 0);
+  av_t *av = Av_val(_av);
+  int index = StreamIndex_val(_stream);
+  AVStream *st = av->format_context->streams[index];
+
+  if (_avg_frame_rate == Val_none)
+    st->avg_frame_rate = (AVRational){0, 1};
+
+  st->avg_frame_rate = rational_of_value(Field(_avg_frame_rate, 0));
+
+  CAMLreturn(Val_unit);
+}
+
 CAMLprim value ocaml_av_get_stream_time_base(value _stream) {
   CAMLparam1(_stream);
   CAMLlocal2(ans, _av);

examples/remuxing.ml

@@ -29,7 +29,9 @@ let () =
     ivss
     |> List.map (fun (i, stream, _) ->
            let params = Av.get_codec_params stream in
-           (i, Av.new_stream_copy ~params dst))
+           let s = Av.new_stream_copy ~params dst in
+           Av.set_avg_frame_rate s (Av.get_avg_frame_rate stream);
+           (i, s))
   in
 
   let isss = Av.get_subtitle_streams src in