[FFmpeg-devel] [PATCH] Support block-level quantization in Theora

[Michael Niedermayer]

On Thu, May 28, 2009 at 01:32:02PM -0400, David Conrad wrote:
> Hi,
>
> This mostly fixes theora_derf.ogg [1]; keyframes are good but interframes 
> degrade due to a bug in libtheora when that file was created (inter quant 
> matrices were assumed to be copied from intra when they shouldn't have been 
> according to the spec.)
>
> Also I reduced the number of planes in qmat to 3 because Theora/vp3 can't 
> have more.
>
> [1] 
> http://ftp.icm.edu.pl/pub/unix/video/mplayer/samples/ogg/Theora/theora_derf.ogg
>

> commit c1a1975b43c1c4f1a2ec62a556348455828a22dd
> Author: David Conrad <lessen42 at gmail.com>
> Date:   Thu May 28 13:30:57 2009 -0400
> 
>     Support block-level quantization in Theora
> 
> diff --git a/libavcodec/vp3.c b/libavcodec/vp3.c
> index 9f7dfb6..5d4be28 100644
> --- a/libavcodec/vp3.c
> +++ b/libavcodec/vp3.c
> @@ -60,6 +60,7 @@ typedef struct Vp3Fragment {
>      uint8_t coding_method;
>      int8_t motion_x;
>      int8_t motion_y;
> +    uint8_t qi;
>  } Vp3Fragment;

what is qi ?
is it what everyone but xiph calls qp? if so i would prefer to follow
what the majority calls it.


[...]
> @@ -477,10 +478,10 @@ static void init_frame(Vp3DecodeContext *s, GetBitContext *gb)
>   * This function sets up the dequantization tables used for a particular
>   * frame.
>   */
> -static void init_dequantizer(Vp3DecodeContext *s)
> +static void init_dequantizer(Vp3DecodeContext *s, int qi)
>  {
> -    int ac_scale_factor = s->coded_ac_scale_factor[s->quality_index];
> -    int dc_scale_factor = s->coded_dc_scale_factor[s->quality_index];

> +    int ac_scale_factor = s->coded_ac_scale_factor[s->qis[qi]];
> +    int dc_scale_factor = s->coded_dc_scale_factor[s->qis[qi]];

qis is hardly a better name than qi btw ...
"quality_index" at least made some sense

[...]
> @@ -963,6 +966,56 @@ static int unpack_vectors(Vp3DecodeContext *s, GetBitContext *gb)
>      return 0;
>  }
>  
> +static int unpack_block_qis(Vp3DecodeContext *s, GetBitContext *gb)
> +{
> +    int qi, i, j, bit, run_length, blocks_decoded, num_blocks_at_qi;
> +    int num_blocks = s->coded_fragment_list_index;
> +
> +    for (qi = 0; qi < s->nqis-1 && num_blocks > 0; qi++) {
> +        i = blocks_decoded = num_blocks_at_qi = 0;
> +
> +        bit = get_bits1(gb);
> +
> +        do {

> +            run_length = get_vlc2(gb, s->superblock_run_length_vlc.table, 6, 2);
> +            if (run_length == 33)
> +                run_length += get_bits(gb, 12);

> +            run_length++;

run_length = get_vlc2(gb, s->superblock_run_length_vlc.table, 6, 2) + 1;


> +            blocks_decoded += run_length;
> +

> +            if (bit) {
> +                for (j = 0; j < run_length; i++) {
> +                    if (i > s->coded_fragment_list_index)
> +                        return -1;
> +
> +                    if (s->all_fragments[s->coded_fragment_list[i]].qi == qi) {
> +                        s->all_fragments[s->coded_fragment_list[i]].qi++;
> +                        j++;
> +                    }
> +                }
> +            } else {
> +                num_blocks_at_qi += run_length;
> +                for (j = 0; j < run_length; i++) {
> +                    if (i > s->coded_fragment_list_index)
> +                        return -1;
> +
> +                    if (s->all_fragments[s->coded_fragment_list[i]].qi == qi)
> +                        j++;
> +                }
> +            }

this could be factorized, though tht would be slower, by a hair in theory
what effect on the whole does this have speedwise?

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

In fact, the RIAA has been known to suggest that students drop out
of college or go to community college in order to be able to afford
settlements. -- The RIAA
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