Configurable CRF (#34)

* Added CRF support

* fixed gop parameter in the README examples

* PR review fixes

---------

Co-authored-by: Alexey Shtern <alexey.shtern@xtend.me>

Author: shtern

README.md

@@ -84,15 +84,16 @@ The plugin has a few parameters that allow for some amount of control.
 - ``gop_size``: The number of frames inbetween keyframes. Default is ``15``.
   The larger this number the more latency you will have, but also the more efficient
   the transmission becomes.
-- ``bit_rate``: The max bit rate [in bits/s] that the encoding will target. Default is ``8242880`.
+- ``bit_rate``: The max bit rate [in bits/s] that the encoding will target. Default is ``8242880``.
+- ``crf``: Constant Rate Factor, affects the image quality. Value range is ``[0, 51]``; ``0`` is lossless, ``23`` is default, ``51`` is worst quality.
 
 The parameters are under the ``ffmpeg_image_transport`` variable block. So if you launch
 your publisher node (camera driver), you can give it a parameter list on the way like so:
 ```
         parameters=[{'ffmpeg_image_transport.encoding': 'hevc_nvenc',
                      'ffmpeg_image_transport.profile': 'main',
                      'ffmpeg_image_transport.preset': 'll',
-                     'ffmpeg_image_transport.gop': 15}]
+                     'ffmpeg_image_transport.gop_size': 15}]
 ```
 
 ### Subscriber (viewer)
@@ -189,7 +190,7 @@ nvmpi like so:
         parameters=[{'ffmpeg_image_transport.encoding': 'h264_nvmpi',
                      'ffmpeg_image_transport.profile': 'main',
                      'ffmpeg_image_transport.preset': 'll',
-                     'ffmpeg_image_transport.gop': 15}]
+                     'ffmpeg_image_transport.gop_size': 15}]
 ```
 
 

include/ffmpeg_image_transport/ffmpeg_encoder.hpp

@@ -138,6 +138,7 @@ class FFMPEGEncoder
   std::string preset_;     // e.g. "slow", "medium", "lossless"
   std::string profile_;    // e.g. "main", "high", "rext"
   std::string tune_;       // e.g. "tune"
+  std::string crf_;        // Range is [0, 51]; 0 is lossless, 23 is default, 51 is worst quality.
   std::string delay_;      // default is 4 frames for parallel processing. 0 is lowest latency
   int qmax_{0};            // max allowed quantization. The lower the better quality
   int GOPSize_{15};        // distance between two keyframes

src/ffmpeg_encoder.cpp

@@ -96,6 +96,7 @@ void FFMPEGEncoder::setParameters(rclcpp::Node * node)
   preset_ = get_safe_param<std::string>(node, ns + "preset", "");
   tune_ = get_safe_param<std::string>(node, ns + "tune", "");
   delay_ = get_safe_param<std::string>(node, ns + "delay", "");
+  crf_ = get_safe_param<std::string>(node, ns + "crf", "");
   qmax_ = get_safe_param<int>(node, ns + "qmax", 10);
   bitRate_ = get_safe_param<int64_t>(node, ns + "bit_rate", 8242880);
   GOPSize_ = get_safe_param<int64_t>(node, ns + "gop_size", 15);
@@ -227,6 +228,7 @@ void FFMPEGEncoder::doOpenCodec(int width, int height)
   setAVOption("preset", preset_);
   setAVOption("tune", tune_);
   setAVOption("delay", delay_);
+  setAVOption("crf", crf_);
   RCLCPP_DEBUG(
     logger_,
     "codec: %10s, profile: %10s, preset: %10s,"