All-
"The sample rate converter is not an encoder ..."
Indeed, an encoder creates a compressed bitstream from audio data (typically linear PCM samples), normally for transmission of some type. A sample rate converter generates audio data from audio data, and is normally applied prior to an encoder because it can only accept a limited range of sample rates.
-Jeff
Quoting Pierre-Louis Bossart pierre-louis.bossart@linux.intel.com:
On 8/6/24 12:26, Shengjiu Wang wrote:
Add Sample Rate Converter(SRC) codec support, define the output format and rate for SRC.
Signed-off-by: Shengjiu Wang shengjiu.wang@nxp.com
include/uapi/sound/compress_offload.h | 2 ++ include/uapi/sound/compress_params.h | 9 ++++++++- 2 files changed, 10 insertions(+), 1 deletion(-)
diff --git a/include/uapi/sound/compress_offload.h b/include/uapi/sound/compress_offload.h index 98772b0cbcb7..8b2b72f94e26 100644 --- a/include/uapi/sound/compress_offload.h +++ b/include/uapi/sound/compress_offload.h @@ -112,10 +112,12 @@ struct snd_compr_codec_caps {
- end of the track
- @SNDRV_COMPRESS_ENCODER_DELAY: no of samples inserted by the
encoder at the
- beginning of the track
- @SNDRV_COMPRESS_SRC_RATIO_MOD: Resampling Ratio Modifier for
sample rate converter */ enum sndrv_compress_encoder { SNDRV_COMPRESS_ENCODER_PADDING = 1, SNDRV_COMPRESS_ENCODER_DELAY = 2,
- SNDRV_COMPRESS_SRC_RATIO_MOD = 3,
};
this sounds wrong to me. The sample rate converter is not an "encoder", and the properties for padding/delay are totally specific to an encoder function.
The other point is that I am not sure how standard this ratio_mod parameter is. This could be totally specific to a specific implementation, and another ASRC might have different parameters.
/** diff --git a/include/uapi/sound/compress_params.h b/include/uapi/sound/compress_params.h index ddc77322d571..0843773ea6b4 100644 --- a/include/uapi/sound/compress_params.h +++ b/include/uapi/sound/compress_params.h @@ -43,7 +43,8 @@ #define SND_AUDIOCODEC_BESPOKE ((__u32) 0x0000000E) #define SND_AUDIOCODEC_ALAC ((__u32) 0x0000000F) #define SND_AUDIOCODEC_APE ((__u32) 0x00000010) -#define SND_AUDIOCODEC_MAX SND_AUDIOCODEC_APE +#define SND_AUDIOCODEC_SRC ((__u32) 0x00000011) +#define SND_AUDIOCODEC_MAX SND_AUDIOCODEC_SRC
I am not sure this is wise to change such definitions?
/*
- Profile and modes are listed with bit masks. This allows for a
@@ -324,6 +325,11 @@ struct snd_dec_ape { __u32 seek_table_present; } __attribute__((packed, aligned(4)));
+struct snd_dec_src {
- __u32 format_out;
- __u32 rate_out;
+} __attribute__((packed, aligned(4)));
Again I am not sure how standard those parameters are, and even if they were if their representation is reusable.
And the compressed API has a good split between encoders and decoders, I am not sure how an SRC can be classified as either.
union snd_codec_options { struct snd_enc_wma wma; struct snd_enc_vorbis vorbis; @@ -334,6 +340,7 @@ union snd_codec_options { struct snd_dec_wma wma_d; struct snd_dec_alac alac_d; struct snd_dec_ape ape_d;
- struct snd_dec_src src;
} __attribute__((packed, aligned(4)));
/** struct snd_codec_desc - description of codec capabilities