feat: Log configs (#225)

Log simplified versions of the config files to stderr. May be useful in
services, to look at logs later to understand when configs changed, and
how they may have impacted performance.

shaka-streamer

@@ -26,6 +26,7 @@ https://shaka-project.github.io/shaka-streamer/
 """
 
 import argparse
+import json
 import sys
 import time
 import yaml
@@ -84,6 +85,12 @@ See docs: https://shaka-project.github.io/shaka-streamer/cloud_storage.html
                       help='Use FFmpeg, FFprobe and Shaka Packager binaries ' +
                            'found in PATH instead of the ones offered by ' +
                            'Shaka Streamer.')
+  parser.add_argument('--log-configs',
+                      action='store_true',
+                      help='Log simplified versions of the config files to ' +
+                           'stderr. May be useful in services, to look at ' +
+                           'logs later to understand when configs changed, ' +
+                           'and how they may have impacted performance.')
 
   args = parser.parse_args()
 
@@ -100,6 +107,14 @@ See docs: https://shaka-project.github.io/shaka-streamer/cloud_storage.html
     with open(args.bitrate_config) as f:
       bitrate_config_dict = yaml.safe_load(f)
 
+  if args.log_configs:
+    configs = {
+      'input': input_config_dict,
+      'pipeline': pipeline_config_dict,
+      'bitrate': bitrate_config_dict,
+    }
+    print('Configs: {}'.format(json.dumps(configs)), file=sys.stderr)
+
   try:
     if args.cloud_url:
       print('Warning: -c/--cloud-url is deprecated; use -o/--output instead',