add prefix to VAAPI specific options

- low power is VAAPI specific\
- compression level is codec/encoder dependent
  - clarify above and VAAPI meaning

Implements #38

README.md

@@ -118,7 +118,7 @@ There are just 4 functions and 3 user-visible data types:
 ```C
 	struct hve_config hardware_config = {WIDTH, HEIGHT, INPUT_WIDTH, INPUT_HEIGHT, FRAMERATE,
 	                                     DEVICE, ENCODER, PIXEL_FORMAT, PROFILE, BFRAMES,
-	                                     BITRATE, QP, GOP_SIZE, COMPRESSION_LEVEL, LOW_POWER};
+	                                     BITRATE, QP, GOP_SIZE, COMPRESSION_LEVEL, VAAPI_LOW_POWER};
 
 	struct hve *hardware_encoder=hve_init(&hardware_config);
 	struct hve_frame frame = { 0 };

examples/hve_encode_raw_h264.c

@@ -29,7 +29,7 @@ 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
-const int LOW_POWER=0; //alternative limited low-power encoding path if non-zero
+const int VAAPI_LOW_POWER=0; //alternative VAAPI limited low-power encoding path if non-zero
 
 int encoding_loop(struct hve *hardware_encoder, FILE *output_file);
 int process_user_input(int argc, char* argv[]);
@@ -45,7 +45,7 @@ int main(int argc, char* argv[])
 	//prepare library data
 	struct hve_config hardware_config = {WIDTH, HEIGHT, INPUT_WIDTH, INPUT_HEIGHT, FRAMERATE,
 	                                     DEVICE, ENCODER, PIXEL_FORMAT, PROFILE, BFRAMES,
-	                                     BITRATE, QP, GOP_SIZE, COMPRESSION_LEVEL, LOW_POWER};
+	                                     BITRATE, QP, GOP_SIZE, COMPRESSION_LEVEL, VAAPI_LOW_POWER};
 	struct hve *hardware_encoder;
 
 	//prepare file for raw H.264 output

examples/hve_encode_raw_hevc10.c

@@ -29,7 +29,7 @@ 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
-const int LOW_POWER=0; //alternative limited low-power encoding path if non-zero
+const int VAAPI_LOW_POWER=0; //alternative VAAPI limited low-power encoding path if non-zero
 
 int encoding_loop(struct hve *hardware_encoder, FILE *output_file);
 int process_user_input(int argc, char* argv[]);
@@ -45,7 +45,7 @@ int main(int argc, char* argv[])
 	//prepare library data
 	struct hve_config hardware_config = {WIDTH, HEIGHT, INPUT_WIDTH, INPUT_HEIGHT, FRAMERATE,
 	                                     DEVICE, ENCODER, PIXEL_FORMAT, PROFILE, BFRAMES,
-	                                     BITRATE, QP, GOP_SIZE, COMPRESSION_LEVEL, LOW_POWER};
+	                                     BITRATE, QP, GOP_SIZE, COMPRESSION_LEVEL, VAAPI_LOW_POWER};
 	struct hve *hardware_encoder;
 
 	//prepare file for raw HEVC output

hve.c

@@ -131,7 +131,7 @@ struct hve *hve_init(const struct hve_config *config)
 	if(config->qp && av_dict_set_int(&opts, "qp", config->qp, 0) < 0)
 		return hve_close_and_return_null(h, "failed to initialize option dictionary (qp)");
 
-	if(config->low_power && av_dict_set_int(&opts, "low_power", config->low_power != 0, 0) < 0)
+	if(config->vaapi_low_power && av_dict_set_int(&opts, "low_power", config->vaapi_low_power != 0, 0) < 0)
 		return hve_close_and_return_null(h, "failed to initialize option dictionary (low_power)");
 
 	if((err = avcodec_open2(h->avctx, codec, &opts)) < 0)

hve.h

@@ -137,12 +137,13 @@ 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 (VAAPI specific) is speed-quality trade-off. Use 0 for driver default.
+ * The compression_level is codec/encoder specific
+ * For VAAPI it 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.
  *
- * The low_power (VAAPI specific) enables alternative encoding path available on some Intel platforms.
+ * The vaapi_low_power (VAAPI specific) enables alternative encoding path available on some Intel platforms.
  *
  * You may check support with vainfo (entrypoints ending with LP):
  * @code
@@ -172,8 +173,8 @@ 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 (VAAPI specific)
-	int low_power; //!< alternative limited low-power encoding if non-zero (VAAPI specific)
+	int compression_level; //!< encoder/codec dependent, 0 for default, for VAAPI 1-7 speed-quality tradeoff, 1 highest quality, 7 fastest
+	int vaapi_low_power; //!< VAAPI specific alternative limited low-power encoding if non-zero
 };
 
 /**