diff --git a/README.md b/README.md
index 20fcadec..b6c83032 100644
--- a/README.md
+++ b/README.md
@@ -54,6 +54,7 @@ Ultimate camera streaming application with support RTSP, WebRTC, HomeKit, FFmpeg
     * [Source: FFmpeg Device](#source-ffmpeg-device)
     * [Source: Exec](#source-exec)
     * [Source: Echo](#source-echo)
+    * [Source: Expr](#source-expr)
     * [Source: HomeKit](#source-homekit)
     * [Source: Bubble](#source-bubble)
     * [Source: DVRIP](#source-dvrip)
@@ -186,6 +187,7 @@ Available source types:
 - [ffmpeg:device](#source-ffmpeg-device) - local USB Camera or Webcam
 - [exec](#source-exec) - get media from external app output
 - [echo](#source-echo) - get stream link from bash or python
+- [expr](#source-expr) - get stream link via built-in expression language
 - [homekit](#source-homekit) - streaming from HomeKit Camera
 - [bubble](#source-bubble) - streaming from ESeeCloud/dvr163 NVR
 - [dvrip](#source-dvrip) - streaming from DVR-IP NVR
@@ -426,6 +428,10 @@ streams:
   apple_hls: echo:python3 hls.py https://developer.apple.com/streaming/examples/basic-stream-osx-ios5.html
 ```
 
+#### Source: Expr
+
+Like `echo` source, but uses the built-in [expr](https://github.com/antonmedv/expr) expression language ([read more](https://github.com/AlexxIT/go2rtc/blob/master/internal/expr/README.md)).
+
 #### Source: HomeKit
 
 **Important:**
diff --git a/internal/expr/README.md b/internal/expr/README.md
index c1f38cb1..35e3c612 100644
--- a/internal/expr/README.md
+++ b/internal/expr/README.md
@@ -1,12 +1,91 @@
+# Expr
+
+[Expr](https://github.com/antonmedv/expr) - expression language and expression evaluation for Go.
+
+- [language definition](https://expr.medv.io/docs/Language-Definition) - takes best from JS, Python, Jinja2 syntax
+- your expression should return a link of any supported source
+- expression supports multiple operation, but:
+  - all operations must be separated by a semicolon
+  - all operations, except the last one, must declare a new variable (`let s = "abc";`)
+  - the last operation should return a string
+- go2rtc supports additional functions:
+  - `fetch` - JS-like HTTP requests
+  - `match` - JS-like RegExp queries
+
+## Examples
+
+**Two way audio for Dahua VTO**
+
+```yaml
+streams:
+  dahua_vto: |
+    expr: let host = "admin:password@192.168.1.123";
+    fetch("http://"+host+"/cgi-bin/configManager.cgi?action=setConfig&Encode[0].MainFormat[0].Audio.Compression=G.711A&Encode[0].MainFormat[0].Audio.Frequency=8000").ok
+        ? "rtsp://"+host+"/cam/realmonitor?channel=1&subtype=0&unicast=true&proto=Onvif" : ""
+```
+
+**dom.ru**
+
+You can get credentials via:
+
+- https://github.com/alexmorbo/domru (file `/share/domru/accounts`)
+- https://github.com/ad/domru
+
+```yaml
+streams:
+  dom_ru: |
+    expr: let camera = "99999999"; let token = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"; let operator = 99;
+    fetch("https://myhome.novotelecom.ru/rest/v1/forpost/cameras/"+camera+"/video", {
+      headers: {Authorization: "Bearer "+token, Operator: operator}
+    }).json().data.URL
+```
+
+**Parse HLS files from Apple**
+
+Same example in two languages - python and expr.
+
+```yaml
+streams:
+  example_python: |
+    echo:python -c 'from urllib.request import urlopen; import re
+
+    # url1 = "https://devstreaming-cdn.apple.com/videos/streaming/examples/bipbop_16x9/bipbop_16x9_variant.m3u8"
+    html1 = urlopen("https://developer.apple.com/streaming/examples/basic-stream-osx-ios5.html").read().decode("utf-8")
+    url1 = re.search(r"https.+?m3u8", html1)[0]
+
+    # url2 = "gear1/prog_index.m3u8"
+    html2 = urlopen(url1).read().decode("utf-8")
+    url2 = re.search(r"^[a-z0-1/_]+\.m3u8$", html2, flags=re.MULTILINE)[0]
+
+    # url3 = "https://devstreaming-cdn.apple.com/videos/streaming/examples/bipbop_16x9/gear1/prog_index.m3u8"
+    url3 = url1[:url1.rindex("/")+1] + url2
+
+    print("ffmpeg:" + url3 + "#video=copy")'
+
+  example_expr: |
+    expr:
+
+    let html1 = fetch("https://developer.apple.com/streaming/examples/basic-stream-osx-ios5.html").text;
+    let url1 = match(html1, "https.+?m3u8")[0];
+
+    let html2 = fetch(url1).text;
+    let url2 = match(html2, "^[a-z0-1/_]+\\.m3u8$", "m")[0];
+
+    let url3 = url1[:lastIndexOf(url1, "/")+1] + url2;
+
+    "ffmpeg:" + url3 + "#video=copy"
+```
+
 ## Comparsion
 
-| expr                     | python                   | js                             |
-|--------------------------|--------------------------|--------------------------------|
-| let x = 1;               | x = 1                    | let x = 1                      |
-| {a: 1, b: 2}             | {"a": 1, "b": 2}         | {a: 1, b: 2}                   |
-| r = fetch(url, {method}) | r = request(method, url) | r = await fetch(url, {method}) |
-| r.ok                     | r.ok                     | r.ok                           |
-| r.status                 | r.status_code            | r.status                       |
-| r.text                   | r.text                   | await r.text()                 |
-| r.json()                 | r.json()                 | await r.json()                 |
-| r.headers                | r.headers                | r.headers                      |
+| expr                         | python                     | js                             |
+|------------------------------|----------------------------|--------------------------------|
+| let x = 1;                   | x = 1                      | let x = 1                      |
+| {a: 1, b: 2}                 | {"a": 1, "b": 2}           | {a: 1, b: 2}                   |
+| let r = fetch(url, {method}) | r = request(method, url)   | r = await fetch(url, {method}) |
+| r.ok                         | r.ok                       | r.ok                           |
+| r.status                     | r.status_code              | r.status                       |
+| r.text                       | r.text                     | await r.text()                 |
+| r.json()                     | r.json()                   | await r.json()                 |
+| r.headers                    | r.headers                  | r.headers                      |
+| let m = match(text, "abc")   | m = re.search("abc", text) | let m = text.match(/abc/)      |