shithub: opus-tools

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Add more comments to opusdec.

--- a/src/opusdec.c

+++ b/src/opusdec.c

@@ -185,6 +185,8 @@

   int mute=_ss->mute;

   b_buf=_ss->b_buf;

   a_buf=_ss->a_buf;

+  /*In order to avoid replacing digital silence with quiet dither noise

+    we mute if the output has been silent for a while*/

   if(mute>64)

     memset(a_buf,0,sizeof(float)*_CC*4);

   for(i=0;i<_n;i++)

@@ -471,7 +473,12 @@

    printf("Copyright (C) 2008-2012 Xiph.Org Foundation\n");

 }

-static OpusMSDecoder *process_header(ogg_packet *op, opus_int32 *rate, int *mapping_family, int *channels, int *preskip, float *gain, float manual_gain, int *streams, int wav_format, int quiet)

+/*Process an Opus header and setup the opus decoder based on it.

+  It takes several pointers for header values which are needed

+  elsewhere in the code.*/

+static OpusMSDecoder *process_header(ogg_packet *op, opus_int32 *rate,

+       int *mapping_family, int *channels, int *preskip, float *gain,

+       float manual_gain, int *streams, int wav_format, int quiet)

 {

    int err;

    OpusMSDecoder *st;

@@ -756,7 +763,9 @@

    }

    inFile=argv_utf8[optind];

+   /*Output to a file or playback?*/

    if (argc_utf8-optind==2){

+     /*If we're outputting to a file, should we apply a wav header?*/

      int i;

      char *ext;

      outFile=argv_utf8[optind+1];

@@ -797,7 +806,15 @@

       close_in=1;

    }

-   /*Init Ogg data struct*/

+   /* .opus files use the Ogg container to provide framing and timekeeping.

+    * http://tools.ietf.org/html/draft-terriberry-oggopus

+    * The easiest way to decode the Ogg container is to use libogg, so

+    *  thats what we do here.

+    * Using libogg is fairly straight forward-- you take your stream of bytes

+    *  and feed them to ogg_sync_ and it periodically returns Ogg pages, you

+    *  check if the pages belong to the stream you're decoding then you give

+    *  them to libogg and it gives you packets. You decode the packets. The

+    *  pages also provide timing information.*/

    ogg_sync_init(&oy);

    /*Main decoding loop*/

@@ -893,6 +910,7 @@

                /*End of stream condition*/

                if (op.e_o_s && os.serialno == opus_serialno)eos=1; /* don't care for anything except opus eos */

+               /*Are we simulating loss for this packet?*/

                if (!lost){

                   /*Decode Opus packet*/

                   ret = opus_multistream_decode_float(st, (unsigned char*)op.packet, op.bytes, output, MAX_FRAME_SIZE, 0);

@@ -917,6 +935,7 @@

                }

                if(!quiet){

+                  /*Display a progress spinner while decoding.*/

                   static const char spinner[]="|/-\\";

                   double coded_seconds = (double)audio_size/(channels*rate*sizeof(short));

                   if(coded_seconds>=last_coded_seconds+1){

@@ -929,6 +948,7 @@

                   }

                }

+               /*If the decoder returned less than zero, we have an error.*/

                if (ret<0)

                {

                   fprintf (stderr, "Decoding error: %s\n", opus_strerror(ret));

@@ -1024,6 +1044,7 @@

       }

    }

+   /*Did we make it to the end without recovering ANY opus logical streams?*/

    if(!total_links)fprintf (stderr, "This doesn't look like a Opus file\n");

    if (stream_init)