obs-ffmpeg: Fix Opus encoder bitrate and errors

The Opus encoder was using the AAC encoder's properties function which
allows bitrates up to 1024 kbps. However, FFmpeg's libopus enforces a
maximum of 256 kbps per channel. Users selecting bitrates above 256
kbps would encounter confusing "Failed to open AAC codec" errors.

This commit adds a dedicated opus_properties() function that sets the
correct bitrate range (64-256 kbps). The 256 kbps limit is more than
sufficient for Opus, as typical WebRTC usage is only 30-90 kbps.

Additionally, fixes hardcoded "AAC codec" error messages in
initialize_codec() to display the actual codec name, improving error
reporting for all FFmpeg audio encoders.

Fixes #12753

Author: thebitbrine

plugins/obs-ffmpeg/obs-ffmpeg-audio-encoders.c

@@ -128,10 +128,10 @@ static bool initialize_codec(struct enc_encoder *enc)
 	ret = avcodec_open2(enc->context, enc->codec, NULL);
 	if (ret < 0) {
 		struct dstr error_message = {0};
-		dstr_printf(&error_message, "Failed to open AAC codec: %s", av_err2str(ret));
+		dstr_printf(&error_message, "Failed to open %s codec: %s", enc->type, av_err2str(ret));
 		obs_encoder_set_last_error(enc->encoder, error_message.array);
 		dstr_free(&error_message);
-		warn("Failed to open AAC codec: %s", av_err2str(ret));
+		warn("Failed to open %s codec: %s", enc->type, av_err2str(ret));
 		return false;
 	}
 	enc->aframe->format = enc->context->sample_fmt;
@@ -422,6 +422,18 @@ static obs_properties_t *enc_properties(void *unused)
 	return props;
 }
 
+static obs_properties_t *opus_properties(void *unused)
+{
+	UNUSED_PARAMETER(unused);
+
+	obs_properties_t *props = obs_properties_create();
+	/* FFmpeg libopus encoder maximum bitrate is 256 kbps per channel.
+	 * For typical stereo/mono usage, 256 kbps provides excellent quality
+	 * (Opus is highly efficient - typical WebRTC usage is 30-90 kbps). */
+	obs_properties_add_int(props, "bitrate", obs_module_text("Bitrate"), 64, 256, 32);
+	return props;
+}
+
 static bool enc_extra_data(void *data, uint8_t **extra_data, size_t *size)
 {
 	struct enc_encoder *enc = data;
@@ -481,7 +493,7 @@ struct obs_encoder_info opus_encoder_info = {
 	.encode = enc_encode,
 	.get_frame_size = enc_frame_size,
 	.get_defaults = enc_defaults,
-	.get_properties = enc_properties,
+	.get_properties = opus_properties,
 	.get_extra_data = enc_extra_data,
 	.get_audio_info = enc_audio_info,
 };