avformat/dashenc: Added a warning for incorrect segment name extension

Applicable only to webm output format.
By default all the segment filenames end with .m4s extension.
When someone chooses webm output format, we recommend they also override the relevant segment name options to end with .webm extension. This patch will issue a warning for he same

libavformat/dashenc.c

@@ -196,6 +196,16 @@ static const char *get_format_str(SegmentType segment_type) {
     return NULL;
 }
 
+static int check_file_extension(const char *filename, const char *extension) {
+    char *dot;
+    if (!filename || !extension)
+        return -1;
+    dot = strrchr(filename, '.');
+    if (dot && !strcmp(dot + 1, extension))
+        return 0;
+    return -1;
+}
+
 static void set_vp9_codec_str(AVFormatContext *s, AVCodecParameters *par,
                               AVRational *frame_rate, char *str, int size) {
     VPCC vpcc;
@@ -987,6 +997,17 @@ static int dash_init(AVFormatContext *s)
         c->format_name = get_format_str(c->segment_type);
         if (!c->format_name)
             return AVERROR_MUXER_NOT_FOUND;
+        if (c->segment_type == SEGMENT_TYPE_WEBM) {
+            if ((!c->single_file && check_file_extension(c->init_seg_name, c->format_name) != 0) ||
+                (!c->single_file && check_file_extension(c->media_seg_name, c->format_name) != 0) ||
+                (c->single_file && check_file_extension(c->single_file_name, c->format_name) != 0)) {
+                av_log(s, AV_LOG_WARNING,
+                       "One or many segment file names doesn't end with .webm. "
+                       "Override -init_seg_name and/or -media_seg_name and/or "
+                       "-single_file_name to end with the extension .webm\n");
+            }
+        }
+
         ctx->oformat = av_guess_format(c->format_name, NULL, NULL);
         if (!ctx->oformat)
             return AVERROR_MUXER_NOT_FOUND;