libobs: Add API to get encoder frame size

When muxing to some format, duration of the packet is used. We need an
API for encoder to return the frame size.

docs/sphinx/reference-encoders.rst

@@ -400,6 +400,12 @@ General Encoder Functions
 
 ---------------------
 
+.. function:: uint32_t obs_encoder_get_frame_size(const obs_encoder_t *encoder)
+
+   :return: The frame size of the audio packet
+
+---------------------
+
 .. function:: void obs_encoder_set_preferred_video_format(obs_encoder_t *encoder, enum video_format format)
               enum video_format obs_encoder_get_preferred_video_format(const obs_encoder_t *encoder)
 

libobs/obs-encoder.c

@@ -760,6 +760,21 @@ uint32_t obs_encoder_get_sample_rate(const obs_encoder_t *encoder)
 		       : audio_output_get_sample_rate(encoder->media);
 }
 
+uint32_t obs_encoder_get_frame_size(const obs_encoder_t *encoder)
+{
+	if (!obs_encoder_valid(encoder, "obs_encoder_get_frame_size"))
+		return 0;
+	if (encoder->info.type != OBS_ENCODER_AUDIO) {
+		blog(LOG_WARNING,
+		     "obs_encoder_get_frame_size: "
+		     "encoder '%s' is not an audio encoder",
+		     obs_encoder_get_name(encoder));
+		return 0;
+	}
+
+	return encoder->framesize != 0 ? encoder->framesize : 0;
+}
+
 void obs_encoder_set_video(obs_encoder_t *encoder, video_t *video)
 {
 	const struct video_output_info *voi;

libobs/obs.h

@@ -2209,6 +2209,9 @@ EXPORT uint32_t obs_encoder_get_height(const obs_encoder_t *encoder);
 /** For audio encoders, returns the sample rate of the audio */
 EXPORT uint32_t obs_encoder_get_sample_rate(const obs_encoder_t *encoder);
 
+/** For audio encoders, returns the frame size of the audio packet */
+EXPORT uint32_t obs_encoder_get_frame_size(const obs_encoder_t *encoder);
+
 /**
  * Sets the preferred video format for a video encoder.  If the encoder can use
  * the format specified, it will force a conversion to that format if the