From 63bf3ae1ae557fc1e0a96f9bc20411d45fa56d27 Mon Sep 17 00:00:00 2001
From: "Steinar H. Gunderson" <steinar+nageru@gunderson.no>
Date: Sun, 4 Apr 2021 12:35:17 +0200
Subject: [PATCH 1/1] Make kaeru insert the aac_adtstoasc filter when needed.

This seemingly fixes mp4 + aac passthrough with no reencoding.
---
 nageru/audio_encoder.h |  1 +
 nageru/kaeru.cpp       | 40 +++++++++++++++++++++++++++++++++++++++-
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/nageru/audio_encoder.h b/nageru/audio_encoder.h
index 3a47f99..ca2634f 100644
--- a/nageru/audio_encoder.h
+++ b/nageru/audio_encoder.h
@@ -30,6 +30,7 @@ public:
 	void encode_audio(const std::vector<float> &audio, int64_t audio_pts);
 	void encode_last_audio();
 
+	const AVCodec *get_codec() const { return ctx->codec; }
 	AVCodecParametersWithDeleter get_codec_parameters();
 
 private:
diff --git a/nageru/kaeru.cpp b/nageru/kaeru.cpp
index 9dc3992..3d2db1c 100644
--- a/nageru/kaeru.cpp
+++ b/nageru/kaeru.cpp
@@ -143,6 +143,30 @@ void raw_packet_callback(Mux *mux, int stream_index, const AVPacket *pkt, AVRati
 	mux->add_packet(*pkt, pkt->pts, pkt->dts == AV_NOPTS_VALUE ? pkt->pts : pkt->dts, timebase, stream_index);
 }
 
+void filter_packet_callback(Mux *mux, int stream_index, AVBSFContext *bsfctx, const AVPacket *pkt, AVRational timebase)
+{
+	AVPacket *in_pkt = av_packet_clone(pkt);
+	unique_ptr<AVPacket, decltype(av_packet_unref) *> in_pkt_cleanup(in_pkt, av_packet_unref);
+	int err = av_bsf_send_packet(bsfctx, in_pkt);
+	if (err < 0) {
+		fprintf(stderr, "av_bsf_send_packet() failed with %d, ignoring\n", err);
+	}
+	for ( ;; ) {
+		AVPacket out_pkt;
+		unique_ptr<AVPacket, decltype(av_packet_unref) *> pkt_cleanup(&out_pkt, av_packet_unref);
+		av_init_packet(&out_pkt);
+		err = av_bsf_receive_packet(bsfctx, &out_pkt);
+		if (err == AVERROR(EAGAIN)) {
+			break;
+		}
+		if (err < 0) {
+			fprintf(stderr, "av_bsf_receive_packet() failed with %d, ignoring\n", err);
+			return;
+		}
+		mux->add_packet(out_pkt, out_pkt.pts, out_pkt.dts == AV_NOPTS_VALUE ? out_pkt.pts : out_pkt.dts, timebase, stream_index);
+	}
+}
+
 void adjust_bitrate(int signal)
 {
 	int new_bitrate = global_flags.x264_bitrate;
@@ -218,7 +242,21 @@ int main(int argc, char *argv[])
 		video.set_video_callback(bind(raw_packet_callback, http_mux.get(), /*stream_index=*/0, _1, _2));
 	}
 	if (!global_flags.transcode_audio && global_flags.enable_audio) {
-		video.set_audio_callback(bind(raw_packet_callback, http_mux.get(), /*stream_index=*/1, _1, _2));
+		AVBSFContext *bsfctx = nullptr;
+		if (strcmp(oformat->name, "mp4") == 0 && strcmp(audio_encoder->get_codec()->name, "aac") == 0) {
+			// We need to insert the aac_adtstoasc filter, seemingly (or we will get warnings to do so).
+			const AVBitStreamFilter *filter = av_bsf_get_by_name("aac_adtstoasc");
+			int err = av_bsf_alloc(filter, &bsfctx);
+			if (err < 0) {
+				fprintf(stderr, "av_bsf_alloc() failed with %d\n", err);
+				exit(1);
+			}
+		}
+		if (bsfctx == nullptr) {
+			video.set_audio_callback(bind(raw_packet_callback, http_mux.get(), /*stream_index=*/1, _1, _2));
+		} else {
+			video.set_audio_callback(bind(filter_packet_callback, http_mux.get(), /*stream_index=*/1, bsfctx, _1, _2));
+		}
 	}
 	video.configure_card();
 	video.start_bm_capture();
-- 
2.39.2