transcode: acodec aliases not supported

The transcode plugin should set the i_codec to the known VLC_FOURCC_* value while probing the encoder. But instead, it leaves the value given by the user.

So for instance, when setting acodec=ulaw, i_codec is not equal to VLC_FOURCC_MULAW (mlaw) and probing fails. The patch is obvious:

diff --git a/modules/stream_out/transcode/audio.c b/modules/stream_out/transcode/audio.c                                                                                                                                                                                       
index f2aa250..047f944 100644
--- a/modules/stream_out/transcode/audio.c
+++ b/modules/stream_out/transcode/audio.c
@@ -251,6 +251,9 @@ int transcode_audio_new( sout_stream_t *p_stream,
     id->p_encoder->fmt_in.audio.i_bitspersample =
         aout_BitsPerSample( id->p_encoder->fmt_in.i_codec );
 
+    id->p_encoder->fmt_out.i_codec =
+        vlc_fourcc_GetCodec( AUDIO_ES, id->p_encoder->fmt_out.i_codec );
+
     id->p_encoder->p_cfg = p_stream->p_sys->p_audio_cfg;
     id->p_encoder->p_module =
         module_need( id->p_encoder, "encoder", p_sys->psz_aenc, true );
@@ -302,10 +305,6 @@ int transcode_audio_new( sout_stream_t *p_stream,
     }
     fmt_last = id->p_encoder->fmt_in;
 
-    /* */
-    id->p_encoder->fmt_out.i_codec =
-        vlc_fourcc_GetCodec( AUDIO_ES, id->p_encoder->fmt_out.i_codec );
-
     return VLC_SUCCESS;
 }

But that patch (probably) breaks MP3 encoding in lavc...