[artwork/transcode] Adjust transcode.c so it can take care of artwork

rescaling, meaning we can do without parallel ffmpeg interfaces.
This also moves artwork rescaling from libswscale to libavfilter, which
seems to fix a problem with PNG rescaling.

src/transcode.h

@@ -22,14 +22,13 @@ enum transcode_profile
 struct decode_ctx;
 struct encode_ctx;
 struct transcode_ctx;
-struct decoded_frame;
 
 // Setting up
 struct decode_ctx *
 transcode_decode_setup(enum transcode_profile profile, enum data_kind data_kind, const char *path, uint32_t song_length);
 
 struct encode_ctx *
-transcode_encode_setup(enum transcode_profile profile, struct decode_ctx *src_ctx, off_t *est_size);
+transcode_encode_setup(enum transcode_profile profile, struct decode_ctx *src_ctx, off_t *est_size, int width, int height);
 
 struct transcode_ctx *
 transcode_setup(enum transcode_profile profile, enum data_kind data_kind, const char *path, uint32_t song_length, off_t *est_size);
@@ -50,51 +49,74 @@ transcode_encode_cleanup(struct encode_ctx **ctx);
 void
 transcode_cleanup(struct transcode_ctx **ctx);
 
-void
-transcode_decoded_free(struct decoded_frame *decoded);
-
 // Transcoding
 
 /* Demuxes and decodes the next packet from the input.
  *
- * @out decoded    A newly allocated struct with a pointer to the frame and the
- *                 stream. Must be freed with transcode_decoded_free().
+ * @out frame      A pointer to the frame. Caller should not free it, that will
+ *                 be done by the next call to the function or by the cleanup
+ *                 function.
  * @in  ctx        Decode context
  * @return         Positive if OK, negative if error, 0 if EOF
  */
 int
-transcode_decode(struct decoded_frame **decoded, struct decode_ctx *ctx);
+transcode_decode(void **frame, struct decode_ctx *ctx);
 
 /* Encodes and remuxes a frame. Also resamples if needed.
  *
  * @out evbuf      An evbuffer filled with remuxed data
- * @in  frame      The frame to encode, e.g. from transcode_decode
  * @in  ctx        Encode context
+ * @in  frame      The decoded frame to encode, e.g. from transcode_decode
+ * @in  eof        If true the muxer will write a trailer to the output
  * @return         Bytes added if OK, negative if error
  */
 int
-transcode_encode(struct evbuffer *evbuf, struct decoded_frame *decoded, struct encode_ctx *ctx);
+transcode_encode(struct evbuffer *evbuf, struct encode_ctx *ctx, void *frame, int eof);
 
 /* Demuxes, decodes, encodes and remuxes from the input.
  *
  * @out evbuf      An evbuffer filled with remuxed data
+ * @out icy_timer  True if METADATA_ICY_INTERVAL has elapsed
+ * @in  ctx        Transcode context
  * @in  want_bytes Minimum number of bytes the caller wants added to the evbuffer
  *                 - set want_bytes to 0 to transcode everything until EOF/error
  *                 - set want_bytes to 1 to get one encoded packet
- * @in  ctx        Transcode context
- * @out icy_timer  True if METADATA_ICY_INTERVAL has elapsed
  * @return         Bytes added if OK, negative if error, 0 if EOF
  */
 int
-transcode(struct evbuffer *evbuf, int want_bytes, struct transcode_ctx *ctx, int *icy_timer);
+transcode(struct evbuffer *evbuf, int *icy_timer, struct transcode_ctx *ctx, int want_bytes);
 
-struct decoded_frame *
-transcode_raw2frame(uint8_t *data, size_t size);
+/* Converts a buffer with raw data to a frame that can be passed directly to the
+ * transcode_encode() function
+ *
+ * @in  profile    Tells the function what kind of frame to create
+ * @in  data       Buffer with raw data
+ * @in  size       Size of buffer
+ * @return         Opaque pointer to frame if OK, otherwise NULL
+ */
+void *
+transcode_frame_new(enum transcode_profile profile, uint8_t *data, size_t size);
+void
+transcode_frame_free(void *frame);
 
-// Seeking
+/* Seek to the specified position - next transcode() will return this packet
+ *
+ * @in  ctx        Transcode context
+ * @in  seek       Requested seek position in ms
+ * @return         Negative if error, otherwise actual seek position
+ */
 int
 transcode_seek(struct transcode_ctx *ctx, int ms);
 
+/* Query for information about a media file opened by transcode_decode_setup()
+ *
+ * @in  ctx        Decode context
+ * @in  query      Query - see implementation for supported queries
+ * @return         Negative if error, otherwise query dependent
+ */
+int
+transcode_decode_query(struct decode_ctx *ctx, const char *query);
+
 // Metadata
 struct http_icy_metadata *
 transcode_metadata(struct transcode_ctx *ctx, int *changed);