add doc for custom filter, catch fatal error: Numerical result *

docs/README.md

@@ -21,6 +21,10 @@ Using live ingest to inject a live stream.
 
 The different output modes.
 
+### **[Custom Filter](/docs/custom_filters.md)**
+
+Apply self defined audio/video filters.
+
 ### **[Preview Stream](/docs/preview_stream.md)**
 
 Setup and use a preview stream.

docs/custom_filters.md

@@ -0,0 +1,29 @@
+## Custom filter
+
+ffplayout allows it to define a custom filter string. For that is the parameter **custom_filter** in the ffplayout.yml config file.
+The filter outputs should end with `[c_v_out]` for video filter, and `[c_a_out]` for audio filter. The filters will be apply on every clip and after the filters which unify the clips.
+
+It is possible to apply only video or audio filters, or both. For a better understanding here some examples:
+
+#### Apply Gaussian blur and volume filter:
+
+```YAML
+custom_filter: 'gblur=5[c_v_out];volume=0.5[c_a_out]'
+```
+
+#### Add lower third:
+
+```YAML
+custom_filter: '[v_in];movie=/path/to/lower_third.png:loop=0,scale=1024:576,setpts=N/(25*TB)[lower];[v_in][lower]overlay=0:0:shortest=1[c_v_out]'
+```
+
+Pay attention to the filter prefix `[v_in];`, this is necessary to get the output from the regular filters.
+
+#### Paint effect
+
+```YAML
+custom_filter: edgedetect=mode=colormix:high=0[c_v_out]
+```
+
+Check ffmpeg [filters](https://ffmpeg.org/ffmpeg-filters.html) documentation, and find out which other filters ffmpeg has.
+

lib/src/utils/mod.rs

@@ -670,7 +670,7 @@ pub fn stderr_reader(buffer: BufReader<ChildStderr>, suffix: &str, mut proc_cont
                 format_log_line(line.clone(), "fatal")
             );
 
-            if line.contains("Invalid argument") {
+            if line.contains("Invalid argument") || line.contains("Numerical result") {
                 proc_control.kill_all();
                 exit(1);
             }