[opus] [opus-tools] [PATCH] Add channel-mapping argument to force channel mapping

[Michael Graczyk]

This patch adds a new option "channel-mapping" to opusenc which sets
the channel mapping family used by the multistream encoder. Please let
me know whether adding this option is worthwhile and whether the help
string is okay. I tried to keep it short but accurate.

The error message for an unimplemented channel mapping is "Error
cannot create encoder: request not implemented". I do not think that
is descriptive enough, but I also do not know of a way to determine
which channel mapping families are supported by the multistream
encoder. If we hard-code valid channel mappings {0, 1, 255}, opusenc
will need to be updated when channel mappings are added to Opus.

With this patch, you can encode four streams independently with
$ opusenc --channel-mapping 255 in.wav out.opus

When channel mapping families are added to Opus in the future
(ambisonics, for example), this option will make it possible to use
them.

---
 src/opusenc.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/src/opusenc.c b/src/opusenc.c
index 0f83194..f2c7c48 100644
--- a/src/opusenc.c
+++ b/src/opusenc.c
@@ -137,6 +137,8 @@ void usage(void)
   printf(" --framesize n      Maximum frame size in milliseconds\n");
   printf("                      (2.5, 5, 10, 20, 40, 60, default: 20)\n");
   printf(" --expect-loss      Percentage packet loss to expect
(default: 0)\n");
+  printf(" --channel-mapping  Channel Mapping Family\n");
+  printf("                      (default: {0, 1, 255} for {1-2, 3-8,
9+} channels)\n");
   printf(" --downmix-mono     Downmix to mono\n");
   printf(" --downmix-stereo   Downmix to stereo (if >2 channels)\n");
   printf(" --max-delay n      Maximum container delay in milliseconds\n");
@@ -260,6 +262,7 @@ int main(int argc, char **argv)
     {"complexity", required_argument, NULL, 0},
     {"framesize", required_argument, NULL, 0},
     {"expect-loss", required_argument, NULL, 0},
+    {"channel-mapping", required_argument, NULL, 0},
     {"downmix-mono",no_argument,NULL, 0},
     {"downmix-stereo",no_argument,NULL, 0},
     {"no-downmix",no_argument,NULL, 0},
@@ -337,6 +340,7 @@ int main(int argc, char **argv)
   opus_int32         coding_rate=48000;
   opus_int32         frame_size=960;
   int                chan=2;
+  int                channel_mapping=-1;
   int                with_hard_cbr=0;
   int                with_cvbr=0;
   int                expect_loss=0;
@@ -465,6 +469,12 @@ int main(int argc, char **argv)
             fprintf(stderr,"Expected loss is a percent and must be 0-100.\n");
             exit(1);
           }
+        }else if(strcmp(long_options[option_index].name,"channel-mapping")==0){
+          channel_mapping=atoi(optarg);
+          if(channel_mapping < 0 || channel_mapping > 255){
+            fprintf(stderr,"Invalid channel-mapping: %s\n",optarg);
+            exit(1);
+          }
         }else if(strcmp(long_options[option_index].name,"comp")==0 ||
                  strcmp(long_options[option_index].name,"complexity")==0){
           complexity=atoi(optarg);
@@ -692,7 +702,11 @@ int main(int argc, char **argv)

   /*OggOpus headers*/ /*FIXME: broke forcemono*/
   header.channels=chan;
-  header.channel_mapping=header.channels>8?255:chan>2;
+  if (channel_mapping >= 0) {
+     header.channel_mapping = channel_mapping;
+  } else {
+     header.channel_mapping = header.channels > 8 ? 255 : header.channels > 2;
+  }
   header.input_sample_rate=rate;
   header.gain=inopt.gain;

-- 

Thanks,
Michael Graczyk