ffmpeg plugin: when decoded stream duration is unavailable, attempt fallback to…

NEWS

 ver 0.20.11 (not yet released)
 * storage
   - curl: support Content-Type application/xml
+* decoder
+  - ffmpeg: more reliable song duration
 
 ver 0.20.10 (2017/08/24)
 * decoder

src/decoder/plugins/FfmpegDecoderPlugin.cxx

@@ -712,7 +712,9 @@ FfmpegDecode(DecoderClient &client, InputStream &input,
 #endif
 
 	const SignedSongTime total_time =
-		FromFfmpegTimeChecked(av_stream.duration, av_stream.time_base);
+		av_stream.duration != (int64_t)AV_NOPTS_VALUE
+		? FromFfmpegTimeChecked(av_stream.duration, av_stream.time_base)
+		: FromFfmpegTimeChecked(format_context.duration, AV_TIME_BASE_Q);
 
 	client.Ready(audio_format, input.IsSeekable(), total_time);
 
@@ -842,6 +844,10 @@ FfmpegScanStream(AVFormatContext &format_context,
 		tag_handler_invoke_duration(handler, handler_ctx,
 					    FromFfmpegTime(stream.duration,
 							   stream.time_base));
+	else if (format_context.duration != (int64_t)AV_NOPTS_VALUE)
+		tag_handler_invoke_duration(handler, handler_ctx,
+					    FromFfmpegTime(format_context.duration,
+							   AV_TIME_BASE_Q));
 
 	FfmpegScanMetadata(format_context, audio_stream, handler, handler_ctx);