lavc: add codec descriptors.

They describe properties that are inherent to a codec (as described by
an AVCodecID) without referring to a specific implementation.

libavcodec/Makefile

@@ -16,6 +16,7 @@ OBJS = allcodecs.o                                                      \
        avpacket.o                                                       \
        bitstream.o                                                      \
        bitstream_filter.o                                               \
+       codec_desc.o                                                     \
        dsputil.o                                                        \
        faanidct.o                                                       \
        fmtconvert.o                                                     \

libavcodec/avcodec.h

@@ -435,6 +435,26 @@ enum AVCodecID {
 #define CodecID AVCodecID
 #endif
 
+/**
+ * This struct describes the properties of a single codec described by an
+ * AVCodecID.
+ * @see avcodec_get_descriptor()
+ */
+typedef struct AVCodecDescriptor {
+    enum AVCodecID     id;
+    enum AVMediaType type;
+    /**
+     * Name of the codec described by this descriptor. It is non-empty and
+     * unique for each codec descriptor. It should contain alphanumeric
+     * characters and '_' only.
+     */
+    const char      *name;
+    /**
+     * A more descriptive name for this codec. May be NULL.
+     */
+    const char *long_name;
+} AVCodecDescriptor;
+
 #if FF_API_OLD_DECODE_AUDIO
 /* in bytes */
 #define AVCODEC_MAX_AUDIO_FRAME_SIZE 192000 // 1 second of 48khz 32bit audio
@@ -4504,6 +4524,20 @@ int av_codec_is_encoder(AVCodec *codec);
  */
 int av_codec_is_decoder(AVCodec *codec);
 
+/**
+ * @return descriptor for given codec ID or NULL if no descriptor exists.
+ */
+const AVCodecDescriptor *avcodec_descriptor_get(enum AVCodecID id);
+
+/**
+ * Iterate over all codec descriptors known to libavcodec.
+ *
+ * @param prev previous descriptor. NULL to get the first descriptor.
+ *
+ * @return next descriptor or NULL after the last descriptor
+ */
+const AVCodecDescriptor *avcodec_descriptor_next(const AVCodecDescriptor *prev);
+
 /**
  * @}
  */