ffmpeg options: Enable trailing ? for map_channel

The -map option allows for a trailing ? so that an error is not thrown if
the input stream does not exist.
This capability is extended to the map_channel option.
This allows a ffmpeg command not to break if an input channel does not
exist, which can be of use (for instance, scripts processing audio
channels with sources having unset number of audio channels).

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

1 files changed, 20 insertions, 3 deletions

diff --git a/ffmpeg_opt.c b/ffmpeg_opt.c
index 1c4a11ef21..f275f711be 100644
--- a/ffmpeg_opt.c
+++ b/ffmpeg_opt.c
@@ -405,6 +405,11 @@ static int opt_map_channel(void *optctx, const char *opt, const char *arg)
     int n;
     AVStream *st;
     AudioChannelMap *m;
+    char *allow_unused;
+    char *mapchan;
+    mapchan = av_strdup(arg);
+    if (!mapchan)
+        return AVERROR(ENOMEM);
 
     GROW_ARRAY(o->audio_channel_maps, o->nb_audio_channel_maps);
     m = &o->audio_channel_maps[o->nb_audio_channel_maps - 1];
@@ -415,6 +420,7 @@ static int opt_map_channel(void *optctx, const char *opt, const char *arg)
         m->file_idx = m->stream_idx = -1;
         if (n == 1)
             m->ofile_idx = m->ostream_idx = -1;
+        av_free(mapchan);
         return 0;
     }
 
@@ -450,11 +456,22 @@ static int opt_map_channel(void *optctx, const char *opt, const char *arg)
                m->file_idx, m->stream_idx);
         exit_program(1);
     }
+    /* allow trailing ? to map_channel */
+    if (allow_unused = strchr(mapchan, '?'))
+        *allow_unused = 0;
     if (m->channel_idx < 0 || m->channel_idx >= st->codecpar->channels) {
-        av_log(NULL, AV_LOG_FATAL, "mapchan: invalid audio channel #%d.%d.%d\n",
-               m->file_idx, m->stream_idx, m->channel_idx);
-        exit_program(1);
+        if (allow_unused) {
+            av_log(NULL, AV_LOG_VERBOSE, "mapchan: invalid audio channel #%d.%d.%d\n",
+                    m->file_idx, m->stream_idx, m->channel_idx);
+        } else {
+            av_log(NULL, AV_LOG_FATAL,  "mapchan: invalid audio channel #%d.%d.%d\n"
+                    "To ignore this, add a trailing '?' to the map_channel.\n",
+                    m->file_idx, m->stream_idx, m->channel_idx);
+            exit_program(1);
+        }
+
     }
+    av_free(mapchan);
     return 0;
 }