make speed-quality tradeoff configurable

- add compression_level configuration option
- 0 for default
- 1 for the highest quality
- 7 for the fastest

The default in my tests is not set to highest quality.

On my 2017 KabyLake with 848x480@30 HEVC Main10 encoding
, the difference between default and highest quality is:
- 15%/25% GPU render busy
- 7-9 ms/10-12 ms per frame

Related to #6

README.md

@@ -117,8 +117,8 @@ There are just 4 functions and 3 user-visible data types:
 - `hve_close`
 
 ```C
-	struct hve_config hardware_config = {WIDTH, HEIGHT, FRAMERATE, DEVICE,
-			ENCODER, PIXEL_FORMAT, PROFILE, BFRAMES, BITRATE, QP, GOP_SIZE};
+	struct hve_config hardware_config = {WIDTH, HEIGHT, FRAMERATE, DEVICE, ENCODER,
+		PIXEL_FORMAT, PROFILE, BFRAMES, BITRATE, QP, GOP_SIZE, COMPRESSION_LEVEL};
 	struct hve *hardware_encoder=hve_init(&hardware_config);
 	struct hve_frame frame = { 0 };
 

examples/hve_encode_raw_h264.c

@@ -26,6 +26,7 @@ const int BFRAMES=0; //max_b_frames, set to 0 to minimize latency, non-zero to m
 const int BITRATE=0; //average bitrate in VBR mode (bit_rate != 0 and qp == 0)
 const int QP=0; //quantization parameter in CQP mode (qp != 0 and bit_rate == 0)
 const int GOP_SIZE=0; //group of pictures size, 0 for default (determines keyframe period)
+const int COMPRESSION_LEVEL=0; //speed-quality tradeoff, 0 for default, 1 for the highest quality, 7 for the fastest
 
 int encoding_loop(struct hve *hardware_encoder, FILE *output_file);
 int process_user_input(int argc, char* argv[]);
@@ -40,7 +41,7 @@ int main(int argc, char* argv[])
 
 	//prepare library data
 	struct hve_config hardware_config = {WIDTH, HEIGHT, FRAMERATE, DEVICE, ENCODER,
-					PIXEL_FORMAT, PROFILE, BFRAMES, BITRATE, QP, GOP_SIZE};
+			PIXEL_FORMAT, PROFILE, BFRAMES, BITRATE, QP, GOP_SIZE, COMPRESSION_LEVEL};
 	struct hve *hardware_encoder;
 
 	//prepare file for raw H.264 output

examples/hve_encode_raw_hevc10.c

@@ -26,6 +26,7 @@ const int BFRAMES=0; //max_b_frames, set to 0 to minimize latency, non-zero to m
 const int BITRATE=0; //average bitrate in VBR mode (bit_rate != 0 and qp == 0)
 const int QP=0; //quantization parameter in CQP mode (qp != 0 and bit_rate == 0)
 const int GOP_SIZE=0; //group of pictures size, 0 for default (determines keyframe period)
+const int COMPRESSION_LEVEL=0; //speed-quality tradeoff, 0 for default, 1 for the highest quality, 7 for the fastest
 
 int encoding_loop(struct hve *hardware_encoder, FILE *output_file);
 int process_user_input(int argc, char* argv[]);
@@ -40,7 +41,7 @@ int main(int argc, char* argv[])
 
 	//prepare library data
 	struct hve_config hardware_config = {WIDTH, HEIGHT, FRAMERATE, DEVICE, ENCODER,
-					PIXEL_FORMAT, PROFILE, BFRAMES, BITRATE, QP, GOP_SIZE};
+			PIXEL_FORMAT, PROFILE, BFRAMES, BITRATE, QP, GOP_SIZE, COMPRESSION_LEVEL};
 	struct hve *hardware_encoder;
 
 	//prepare file for raw HEVC output

hve.c

@@ -78,6 +78,7 @@ struct hve *hve_init(const struct hve_config *config)
 		h->avctx->profile = config->profile;
 	h->avctx->max_b_frames = config->max_b_frames;
 	h->avctx->bit_rate = config->bit_rate;
+	h->avctx->compression_level = config->compression_level;
 
 	//try to find software pixel format that user wants to upload data in
 	if(config->pixel_format == NULL || config->pixel_format[0] == '\0')

hve.h

@@ -123,6 +123,11 @@ struct hve;
  * Setting gop_size equal to framerate results in one keyframe per second.
  * Use 0 value for default, -1 for intra only.
  *
+ * The compression_level is speed-quality trade-off. Use 0 for driver default.
+ * For highest quality use 1, for fastest encoding use 7.
+ * The default is not highest quality so if you need it, set it explicitly to 1.
+ * The exact interpretation is hardware dependent.
+ *
  * @see hve_init
  */
 struct hve_config
@@ -138,6 +143,7 @@ struct hve_config
 	int bit_rate; //!< average bitrate in VBR mode (bit_rate != 0 and qp == 0)
 	int qp; //!< quantization parameter in CQP mode (qp != 0 and bit_rate == 0)
 	int gop_size; //!<  group of pictures size, 0 for default, -1 for intra only
+	int compression_level; //!< speed-quality tradeoff, 0 for default, 1 for the highest quality, 7 for the fastest
 };
 
 /**