Re: [FFmpeg-devel] [PATCH 1/1] Add vpx range encoder support

[Peter Ross <pross@xvid.org>]

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On Wed, Mar 05, 2025 at 09:59:34PM +0530, MihirGore wrote:
> From: MihirGore23 <mihirvgore@outlook.com>
>

Hi,

comments below.
 
> ---
>  libavcodec/vpx_rac.h | 75 ++++++++++++++++++++++++++++++++++----------
>  1 file changed, 59 insertions(+), 16 deletions(-)
> 
> diff --git a/libavcodec/vpx_rac.h b/libavcodec/vpx_rac.h
> index b158cc0754..f01358f71f 100644
> --- a/libavcodec/vpx_rac.h
> +++ b/libavcodec/vpx_rac.h
> @@ -20,7 +20,7 @@
>  
>  /**
>   * @file
> - * Common VP5-VP9 range decoder stuff
> + * Common VP5-VP9 range encoder and decoder functions
>   */
>  
>  #ifndef AVCODEC_VPX_RAC_H
> @@ -34,24 +34,25 @@
>  
>  typedef struct VPXRangeCoder {
>      int high;
> -    int bits; /* stored negated (i.e. negative "bits" is a positive number of
> -                 bits left) in order to eliminate a negate in cache refilling */
> +    int bits; 
                ^^^^^
there is some some unnecessary whitespace after 'bits;'
also why did you delete the original comment?

>      const uint8_t *buffer;
>      const uint8_t *end;
>      unsigned int code_word;
>      int end_reached;
> +    uint8_t *output_buffer; // Added for encoding
> +    uint8_t *output_end;    // Added for encoding
>  } VPXRangeCoder;
>  
>  extern const uint8_t ff_vpx_norm_shift[256];
> +
> +/*Decoder Functions */
> +
>  int ff_vpx_init_range_decoder(VPXRangeCoder *c, const uint8_t *buf, int buf_size);
>  
> -/**
> - * returns 1 if the end of the stream has been reached, 0 otherwise.
> - */
>  static av_always_inline int vpx_rac_is_end(VPXRangeCoder *c)
>  {
>      if (c->end <= c->buffer && c->bits >= 0)
> -        c->end_reached ++;
> +        c->end_reached++;
>      return c->end_reached > 10;
>  }
>  
> @@ -64,7 +65,7 @@ static av_always_inline unsigned int vpx_rac_renorm(VPXRangeCoder *c)
>      c->high   <<= shift;
>      code_word <<= shift;
>      bits       += shift;
> -    if(bits >= 0 && c->buffer < c->end) {
> +    if (bits >= 0 && c->buffer < c->end) {
>          code_word |= bytestream_get_be16(&c->buffer) << bits;
>          bits -= 16;
>      }
> @@ -72,12 +73,6 @@ static av_always_inline unsigned int vpx_rac_renorm(VPXRangeCoder *c)
>      return code_word;
>  }
>  
> -#if   ARCH_ARM
> -#include "arm/vpx_arith.h"
> -#elif ARCH_X86
> -#include "x86/vpx_arith.h"
> -#endif
> -
>  #ifndef vpx_rac_get_prob
>  #define vpx_rac_get_prob vpx_rac_get_prob
>  static av_always_inline int vpx_rac_get_prob(VPXRangeCoder *c, uint8_t prob)
> @@ -95,7 +90,6 @@ static av_always_inline int vpx_rac_get_prob(VPXRangeCoder *c, uint8_t prob)
>  #endif
>  
>  #ifndef vpx_rac_get_prob_branchy
> -// branchy variant, to be used where there's a branch based on the bit decoded
>  static av_always_inline int vpx_rac_get_prob_branchy(VPXRangeCoder *c, int prob)
>  {
>      unsigned long code_word = vpx_rac_renorm(c);
> @@ -117,7 +111,6 @@ static av_always_inline int vpx_rac_get_prob_branchy(VPXRangeCoder *c, int prob)
>  static av_always_inline int vpx_rac_get(VPXRangeCoder *c)
>  {
>      unsigned int code_word = vpx_rac_renorm(c);
> -    /* equiprobable */
>      int low = (c->high + 1) >> 1;
>      unsigned int low_shift = low << 16;
>      int bit = code_word >= low_shift;
> @@ -132,4 +125,54 @@ static av_always_inline int vpx_rac_get(VPXRangeCoder *c)
>      return bit;
>  }
>  
> +//Encoder Functions
> +
> +int ff_vpx_init_range_encoder(VPXRangeCoder *c, uint8_t *buf, int buf_size);
> +

ff_vpx_init_range_encoder function is not defined anywhere.
did you forget to commit vpx_rac.c changes?

> +static av_always_inline void vpx_rac_flush(VPXRangeCoder *c)
> +{
> +    for (int i = 0; i < 4; i++) {
> +        if (c->output_buffer < c->output_end) {
> +            *c->output_buffer++ = c->code_word >> 24;
> +        }
> +        c->code_word <<= 8;
> +    }
> +}

after calling vpx_rac_flush() how does the caller determine the final size
of the output buffer?

finally, does the output of your encoder work with the existing decoder?
simple test case:

```
    VPXRangeCoder e;
    uint8_t buf[1024] = {0};
    ff_vpx_init_range_encoder(&e, buf, sizeof(buf));
    vpx_rac_put(&e, 1);
    vpx_rac_put(&e, 0);
    vpx_rac_put(&e, 1);
    vpx_rac_flush(&e);

    VPXRangeCoder d;
    ff_vpx_init_range_decoder(&d, buf, e.output_buffer - buf);
    printf("%d\n", vpx_rac_get(&d));
    printf("%d\n", vpx_rac_get(&d));
    printf("%d\n", vpx_rac_get(&d));
```

-- Peter
(A907 E02F A6E5 0CD2 34CD 20D2 6760 79C5 AC40 DD6B)

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