Integrate Constant Rate Factor (CRF) for FFmpegWriter (#186)

* First implementation of CRF (Constant Rate Factor)

* Include AV1 in the codecs that can use crf

* First version that uses SetOption to set crf quality

* Clarify comments

* Delete setting the bitrate for crf in SetVideoOption because it
is not needed, it is set later with SetOptions.

Author: jonoomph

src/FFmpegWriter.cpp

@@ -146,7 +146,7 @@ void FFmpegWriter::SetVideoOptions(bool has_video, string codec, Fraction fps, i
 		info.pixel_ratio.num = pixel_ratio.num;
 		info.pixel_ratio.den = pixel_ratio.den;
 	}
-	if (bit_rate >= 1000)
+	if (bit_rate >= 1000)			// bit_rate is the bitrate in b/s
 		info.video_bit_rate = bit_rate;
 
 	info.interlaced_frame = interlaced;
@@ -237,7 +237,8 @@ void FFmpegWriter::SetOption(StreamType stream, string name, string value)
 
 	// Was option found?
 	if (option || (name == "g" || name == "qmin" || name == "qmax" || name == "max_b_frames" || name == "mb_decision" ||
-			       name == "level" || name == "profile" || name == "slices" || name == "rc_min_rate"  || name == "rc_max_rate"))
+			       name == "level" || name == "profile" || name == "slices" || name == "rc_min_rate"  || name == "rc_max_rate" ||
+					 	 name == "crf"))
 	{
 		// Check for specific named options
 		if (name == "g")
@@ -284,6 +285,39 @@ void FFmpegWriter::SetOption(StreamType stream, string name, string value)
 			// Buffer size
 			convert >> c->rc_buffer_size;
 
+		else if (name == "crf") {
+			// encode quality and special settings like lossless
+			// This might be better in an extra methods as more options
+			// and way to set quality are possible
+			#if  LIBAVCODEC_VERSION_INT >= AV_VERSION_INT(55, 39, 101)
+					switch (c->codec_id) {
+						case AV_CODEC_ID_VP8 :
+							av_opt_set_int(c->priv_data, "crf", min(stoi(value),63), 0);
+							break;
+						case AV_CODEC_ID_VP9 :
+							av_opt_set_int(c->priv_data, "crf", min(stoi(value),63), 0);
+							if (stoi(value) == 0) {
+								av_opt_set_int(c->priv_data, "lossless", 1, 0);
+							 }
+							 break;
+						case AV_CODEC_ID_H264 :
+							av_opt_set_int(c->priv_data, "crf", min(stoi(value),51), 0);
+							break;
+						case AV_CODEC_ID_H265 :
+							av_opt_set_int(c->priv_data, "crf", min(stoi(value),51), 0);
+							if (stoi(value) == 0) {
+								av_opt_set_int(c->priv_data, "lossless", 1, 0);
+							 }
+							break;
+			#ifdef AV_CODEC_ID_AV1
+						case AV_CODEC_ID_AV1 :
+							av_opt_set_int(c->priv_data, "crf", min(stoi(value),63), 0);
+							break;
+			#endif
+					}
+			#endif
+		}
+
 		else
 			// Set AVOption
 			AV_OPTION_SET(st, c->priv_data, name.c_str(), value.c_str(), c);
@@ -934,7 +968,9 @@ AVStream* FFmpegWriter::add_video_stream()
 #endif
 
 	/* Init video encoder options */
-	c->bit_rate = info.video_bit_rate;
+	if (info.video_bit_rate > 1000) {
+		c->bit_rate = info.video_bit_rate;
+	}
 
 	//TODO: Implement variable bitrate feature (which actually works). This implementation throws
 	//invalid bitrate errors and rc buffer underflow errors, etc...