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Doc improvements for --bitrate, and a --quality alias for it.

--- a/man/opusenc.1

+++ b/man/opusenc.1

@@ -100,15 +100,38 @@

 .IP "-V, --version"

 Show the version number

 .IP "--bitrate N.nnn"

-Encoding bitrate in kbit/sec (6-256 per channel)

+Target bitrate in kbit/sec (6-256 per channel)

+

+In VBR mode this specifies the average rate for a large and diverse

+collection of audio. In CVBR and Hard-CBR mode it specifies the specific

+output bitrate.

+

+.IP "--quality N.nnn"

+Target audio quality (6-256 per channel).

+

+In VBR mode this is the same as bitrate: It specifies quality in terms of the

+average rate for a large collection of audio.

 .br

 Default for >=44.1kHz input is 64kbps per mono stream, 96kbps per coupled pair.

 .IP "--vbr"

 Use variable bitrate encoding (default)

+

+In VBR mode the bitrate may go up and down freely depending on the content

+to achieve more consistent quality.

+

 .IP "--cvbr"

-Use constrained variable bitrate encoding

+Use constrained variable bitrate encoding.

+

+Outputs to a specific bitrate. This mode is analogous to CBR in AAC/MP3

+encoders and managed mode in vorbis coders. This delivers less consistent

+quality than VBR mode but consistent bitrate.

 .IP "--hard-cbr"

-Use hard constant bitrate encoding

+Use hard constant bitrate encoding.

+

+With hard-cbr every frame will be exactly the same size, similar to how

+speech codecs work. This delivers lower overall quality but is useful

+ where bitrate changes might leak data in encrypted channels or on

+synchronous transports.

 .IP "--comp N"

 Encoding computational complexity (0-10, default: 10). Zero gives the

 fastest encodes but lower quality, while 10 gives the highest quality

--- a/src/opusenc.c

+++ b/src/opusenc.c

@@ -129,7 +129,8 @@

   printf("  filename.opus     compressed file\n");

   printf("  -                 stdout\n");

   printf("\nEncoding options:\n");

-  printf(" --bitrate n.nnn    Encoding bitrate in kbit/sec (6-256 per channel)\n");

+  printf(" --bitrate n.nnn    Target bitrate in kbit/sec (6-256/channel)\n");

+  printf(" --quality n.nnn    Target quality (6-256/channel; same as bitrate in VBR)\n");

   printf(" --vbr              Use variable bitrate encoding (default)\n");

   printf(" --cvbr             Use constrained variable bitrate encoding\n");

   printf(" --hard-cbr         Use hard constant bitrate encoding\n");

@@ -252,6 +253,7 @@

   {

     {"quiet", no_argument, NULL, 0},

     {"bitrate", required_argument, NULL, 0},

+    {"quality", required_argument, NULL, 0},

     {"hard-cbr",no_argument,NULL, 0},

     {"vbr",no_argument,NULL, 0},

     {"cvbr",no_argument,NULL, 0},

@@ -403,7 +405,8 @@

       case 0:

         if(strcmp(long_options[option_index].name,"quiet")==0){

           quiet=1;

-        }else if(strcmp(long_options[option_index].name,"bitrate")==0){

+        }else if(strcmp(long_options[option_index].name,"bitrate")==0||

+                 strcmp(long_options[option_index].name,"quality")==0){

           bitrate=atof(optarg)*1000.;

         }else if(strcmp(long_options[option_index].name,"hard-cbr")==0){

           with_hard_cbr=1;