Decode audio stream using ffmpeg

src/spek-audio.c

@@ -22,6 +22,7 @@
 
 void spek_audio_init () {
 	avcodec_init ();
+	/* TODO: register only audio decoders */
 	av_register_all ();
 }
 
@@ -70,13 +71,64 @@ SpekAudioContext * spek_audio_open (const char *file_name) {
 		cx->bits_per_sample = cx->codec_context->bits_per_coded_sample;
 	}
 	cx->channels = cx->codec_context->channels;
+	cx->buffer_size = (AVCODEC_MAX_AUDIO_FRAME_SIZE * 3) / 2;
 	if (avcodec_open (cx->codec_context, cx->codec) < 0) {
 		cx->error = _("Cannot open decoder");
 		return cx;
 	}
+	av_init_packet (&cx->packet);
+	cx->offset = 0;
 	return cx;
 }
 
+gint spek_audio_read (SpekAudioContext *cx, guint8 *buffer) {
+	gint buffer_size;
+	gint len;
+	gint res;
+
+	if (cx->error) {
+		return -1;
+	}
+
+	for (;;) {
+		while (cx->packet.size > 0) {
+			buffer_size = cx->buffer_size;
+			len = avcodec_decode_audio3 (
+				cx->codec_context, (int16_t *) buffer, &buffer_size, &cx->packet);
+			if (len < 0) {
+				/* Error, skip the frame. */
+				cx->packet.size = 0;
+				break;
+			}
+			cx->packet.data += len;
+			cx->packet.size -= len;
+			cx->offset += len;
+			if (buffer_size <= 0) {
+				/* No data yet, get more frames */
+				continue;
+			}
+			/* We have data, return it and come back for more later */
+			return buffer_size;
+		}
+		if (cx->packet.data) {
+			cx->packet.data -= cx->offset;
+			cx->packet.size += cx->offset;
+			cx->offset = 0;
+			av_free_packet (&cx->packet);
+		}
+		while ((res = av_read_frame (cx->format_context, &cx->packet)) >= 0) {
+			if (cx->packet.stream_index == cx->audio_stream) {
+				break;
+			}
+			av_free_packet (&cx->packet);
+		}
+		if (res < 0) {
+			/* End of file or error. */
+			return 0;
+		}
+	}
+}
+
 void spek_audio_close (SpekAudioContext *cx) {
 	if (cx->file_name != NULL) {
 		g_free (cx->file_name);
@@ -84,6 +136,12 @@ void spek_audio_close (SpekAudioContext *cx) {
 	if (cx->codec_name != NULL) {
 		g_free (cx->codec_name);
 	}
+	if (cx->packet.data) {
+		cx->packet.data -= cx->offset;
+		cx->packet.size += cx->offset;
+		cx->offset = 0;
+		av_free_packet (&cx->packet);
+	}
 	if (cx->codec_context != NULL) {
 		avcodec_close (cx->codec_context);
 	}

src/spek-audio.h

@@ -24,13 +24,15 @@
 #include <libavcodec/avcodec.h>
 
 typedef struct {
+	/* Internal data */
 	AVFormatContext *format_context;
 	gint audio_stream;
 	AVCodecContext *codec_context;
 	AVCodec *codec;
+	AVPacket packet;
+	gint offset;
 
-	/* Exposed properties
-	 */
+	/* Exposed properties */
 	gchar *file_name;
 	gchar *codec_name;
 	gchar *error;
@@ -38,10 +40,28 @@ typedef struct {
 	gint sample_rate;
 	gint bits_per_sample;
 	gint channels;
+	gint buffer_size; /* minimum buffer size for spek_audio_read() */
 } SpekAudioContext;
 
+/* Initialise FFmpeg, should be called once on start up */
 void spek_audio_init ();
-SpekAudioContext * spek_audio_open (const char *file_name);
+
+/* Open the file, check if it has an audio stream which can be decoded.
+ * On error, initialises the `error` field in the returned context.
+ */
+SpekAudioContext * spek_audio_open (const gchar *file_name);
+
+/* Read and decode the opened audio stream.
+ * Returns -1 on error, 0 if there's nothing left to read
+ * or the number of bytes decoded into the buffer.
+ * The buffer must be allocated (and later freed) by the caller,
+ * minimum size is `buffer_size`.
+ */
+gint spek_audio_read (SpekAudioContext *cx, guint8 *buffer);
+
+/* Closes the file opened with spek_audio_open,
+ * frees all allocated buffers and the context
+ */
 void spek_audio_close (SpekAudioContext *cx);
 
 #endif

src/spek-pipeline.vala

@@ -50,6 +50,9 @@ namespace Spek {
 				// TRANSLATORS: first %s is the error message, second %s is stream description.
 				description = _("%s: %s").printf (cx.error, description);
 			}
+
+			var buffer = new uint8[cx.buffer_size];
+			while (cx.read (buffer) > 0);
 		}
 
 		public string file_name {

src/spek-spectrogram.vala

@@ -65,7 +65,7 @@ namespace Spek {
 
 			// TODO
 			var pipeline = new Pipeline (file_name);
-			print ("%s:\n%s\n", file_name, pipeline.description);
+			print ("\n%s:\n%s\n", file_name, pipeline.description);
 
 			start ();
 		}

vapi/spek-audio.vapi

@@ -10,9 +10,12 @@ namespace Spek.Audio {
 		public int sample_rate;
 		public int bits_per_sample;
 		public int channels;
+		public int buffer_size;
 
 		[CCode (cname = "spek_audio_open")]
 		public Context (string file_name);
+		[CCode (cname = "spek_audio_read")]
+		public int read ([CCode (array_length = false)] uint8[] buffer);
 	}
 	public static void init ();
 }