add audio output - still have some latency

spdif-loop.c

@@ -18,7 +18,7 @@ usage(void)
 {
 	fprintf(stderr,
 		"usage:\n"
-		"  spdif-loop <hw:alsa-input-dev>\n");
+		"  spdif-loop <hw:alsa-input-dev> <alsa|pulse> <output-dev>\n");
 	exit(1);
 }
 
@@ -48,24 +48,69 @@ alsa_reader(void *data, uint8_t *buf, int buf_size)
 	return (ret);
 }
 
+static enum CodecID
+probe_codec(AVFormatContext *s)
+{
+	AVPacket pkt;
+
+	av_init_packet(&pkt);
+	if (av_read_frame(s, &pkt) != 0)
+		return (CODEC_ID_NONE);
+
+	av_free_packet(&pkt);
+
+	if (s->nb_streams == 0)
+		return (CODEC_ID_NONE);
+	return (s->streams[0]->codec->codec_id);
+}
+
+static ao_device *
+open_output(int driver_id, ao_option *dev_opts, AVCodecContext *s)
+{
+        printf("%d bit, %d channels, %dHz\n",
+               av_get_bytes_per_sample(s->sample_fmt) * 8,
+               s->channels,
+               s->sample_rate);
+
+        ao_sample_format out_fmt = {
+                .bits = av_get_bytes_per_sample(s->sample_fmt) * 8,
+                .channels = s->channels,
+                .rate = s->sample_rate,
+                .byte_format = AO_FMT_NATIVE,
+        };
+
+	return (ao_open_live(driver_id, &out_fmt, dev_opts));
+}
+
 int
 main(int argc, char **argv)
 {
-	if (argc != 2)
+	if (argc != 4)
 		usage();
 
-        char *alsa_dev = argv[1];
+	char *alsa_dev_name = argv[1];
+	char *out_driver_name = argv[2];
+	char *out_dev_name = argv[3];
 
 	av_register_all();
 	avcodec_register_all();
-        avdevice_register_all();
+	avdevice_register_all();
+	ao_initialize();
+
+	int out_driver_id = ao_driver_id(out_driver_name);
+	if (out_driver_id < 0)
+		return (17);
+
+	ao_option *out_dev_opts = NULL;
+	if (!ao_append_option(&out_dev_opts, "dev", out_dev_name))
+		return (18);
 
 	AVInputFormat *alsa_fmt = av_find_input_format("alsa");
 	if (!alsa_fmt)
 		return (3);
 
 	AVFormatContext *alsa_ctx = NULL;
-	if (avformat_open_input(&alsa_ctx, alsa_dev, alsa_fmt, NULL) != 0)
+	if (avformat_open_input(&alsa_ctx, alsa_dev_name, alsa_fmt, NULL) != 0)
 		return (2);
 
 	AVFormatContext *spdif_ctx = avformat_alloc_context();
@@ -92,9 +137,66 @@ main(int argc, char **argv)
 	if (avformat_open_input(&spdif_ctx, "internal", spdif_fmt, NULL) != 0)
 		return (7);
 
-	printf("streams: %d\n", spdif_ctx->nb_streams);
-	for (int i = 0; i < spdif_ctx->nb_streams; ++i)
-		printf("\t%d.\t%d\n", i, spdif_ctx->streams[i]->codec->codec_id);
-
+	enum CodecID spdif_codec_id = probe_codec(spdif_ctx);
+
+	printf("detected spdif codec %s\n", avcodec_get_name(spdif_codec_id));
+
+	AVCodec *spdif_codec = avcodec_find_decoder(spdif_codec_id);
+	if (!spdif_codec)
+		return (9);
+	AVCodecContext *spdif_codec_ctx = avcodec_alloc_context3(spdif_codec);
+	if (!spdif_codec_ctx)
+		return (10);
+	spdif_codec_ctx->request_sample_fmt = AV_SAMPLE_FMT_S16;
+	if (avcodec_open2(spdif_codec_ctx, spdif_codec, NULL) != 0)
+		return (11);
+
+	AVPacket pkt, pkt1 = {.size = 0, .data = NULL};
+	av_init_packet(&pkt1);
+	pkt = pkt1;
+
+	AVFrame frame;
+
+	ao_device *out_dev = NULL;
+
+	for (;;) {
+		if (pkt.size == 0) {
+			av_free_packet(&pkt1);
+			if (av_read_frame(spdif_ctx, &pkt1) != 0)
+				return (13);
+			pkt = pkt1;
+		}
+
+		avcodec_get_frame_defaults(&frame);
+		int got_frame = 0;
+		int processed_len = avcodec_decode_audio4(spdif_codec_ctx, &frame, &got_frame, &pkt);
+		if (processed_len < 0)
+			return (14);
+		pkt.data += processed_len;
+		pkt.size -= processed_len;
+
+		if (!got_frame)
+			continue;
+
+
+		if (!out_dev) {
+			/**
+			 * We open the output only here, because we need a full frame decoded
+			 * before we can know the output format.
+			 */
+			out_dev = open_output(out_driver_id, out_dev_opts, spdif_codec_ctx);
+			if (!out_dev)
+				return (15);
+		}
+
+		int framesize = av_samples_get_buffer_size(NULL,
+							   spdif_codec_ctx->channels,
+							   frame.nb_samples,
+							   spdif_codec_ctx->sample_fmt,
+							   1);
+		if (!ao_play(out_dev, (void *)frame.data[0], framesize))
+			return (16);
+	}
+
 	return (0);
 }