ffmpeg: do not compute a duration for streaming streams.

Streaming means the stream is endless, so don't compute a duration.

ffmpeg computes an estimation using what it thinks is the file size, but
is instead some internal buffer size from BAdapterIO.

Fixes second part of #14326.

src/add-ons/media/plugins/ffmpeg/AVCodecDecoder.cpp

@@ -1740,8 +1740,9 @@ AVCodecDecoder::_InitFilterGraph(enum AVPixelFormat pixfmt, int32 width,
 	fFilterGraph = avfilter_graph_alloc();
 
 	BString arguments;
-	arguments.SetToFormat("buffer=video_size=%dx%d:pix_fmt=%d:time_base=1/1:"
-		"pixel_aspect=0/1[in];[in]yadif[out];[out]buffersink", width, height,
+	arguments.SetToFormat("buffer=video_size=%" B_PRId32 "x%" B_PRId32
+		":pix_fmt=%d:time_base=1/1:pixel_aspect=0/1[in];[in]yadif[out];"
+		"[out]buffersink", width, height,
 		pixfmt);
 	AVFilterInOut* inputs = NULL;
 	AVFilterInOut* outputs = NULL;

src/add-ons/media/plugins/ffmpeg/AVFormatReader.cpp

@@ -429,6 +429,12 @@ StreamBase::Duration() const
 	// for a couple of streams and are in line with the documentation, but
 	// unfortunately, libavformat itself seems to set the time_base and
 	// duration wrongly sometimes. :-(
+
+	int32 flags;
+	fSource->GetFlags(&flags);
+	if ((flags & B_MEDIA_STREAMING) != 0)
+		return 0;
+
 	if ((int64)fStream->duration != AV_NOPTS_VALUE)
 		return _ConvertFromStreamTimeBase(fStream->duration);
 	else if ((int64)fContext->duration != AV_NOPTS_VALUE)