Re: [FFmpeg-devel] Misc mpegvideo patches

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Andreas Rheinhardt:
> Ramiro Polla:
>> On Tue, Mar 4, 2025 at 6:05 PM Andreas Rheinhardt
>> <andreas.rheinhardt@outlook.com> wrote:
>>> Ramiro Polla:
>>>>
>>>> On 3/4/25 14:42, Andreas Rheinhardt wrote:
>>>>> (Mostly trivial) patches attached. A branch is at
>>>>> https://github.com/mkver/FFmpeg/tree/mpegvideo_misc
>>>>
>>>>
>>>> [PATCH 10/40] avcodec/mpegvideo_enc: Move default_mv_penalty to h261enc.c
>>>>
>>>>> diff --git a/libavcodec/h261enc.c b/libavcodec/h261enc.c
>>>>> index dabab9d80a..e33bf35a8a 100644
>>>>> --- a/libavcodec/h261enc.c
>>>>> +++ b/libavcodec/h261enc.c
>>>>> @@ -46,6 +46,7 @@ static struct VLCLUT {
>>>>>      uint16_t code;
>>>>>  } vlc_lut[H261_MAX_RUN + 1][32 /* 0..2 * H261_MAX_LEN are used */];
>>>>>
>>>>> +static uint8_t mv_penalty[MAX_FCODE + 1][MAX_DMV * 2 + 1];
>>>>>  static uint8_t uni_h261_rl_len     [64 * 128];
>>>>>  static uint8_t uni_h261_rl_len_last[64 * 128];
>>>>>  static uint8_t h261_mv_codes[64][2];
>>>>> @@ -370,6 +371,8 @@ av_cold int ff_h261_encode_init(MpegEncContext *s)
>>>>>      s->max_qcoeff       = 127;
>>>>>      s->ac_esc_length    = H261_ESC_LEN;
>>>>>
>>>>> +    s->me.mv_penalty = mv_penalty;
>>>>> +
>>>>>      s->intra_ac_vlc_length      = s->inter_ac_vlc_length      =
>>>>> uni_h261_rl_len;
>>>>>      s->intra_ac_vlc_last_length = s->inter_ac_vlc_last_length =
>>>>> uni_h261_rl_len_last;
>>>>>      ff_thread_once(&init_static_once, h261_encode_init_static);
>>>>
>>>> This global mv_penalty doesn't seem to be ever initialized; it could be
>>>> declared const.
>>>
>>> But then it would no longer be placed in .bss, but instead in .rodata
>>> and increase binary size.
>>
>> Wow, that's a huge array.
>>
>>>> But it also makes me think that whatever code is using this mv_penalty,
>>>> which is always set to zero, might be calculating things wrong.
>>>>
>>>
>>> It is obviously done to avoid branches for the codecs that matter. H.261
>>> does not matter much. Apart from that, it is a very cheap workaround
>>> given that this table is .bss.
>>
>> Could you add some comments (either next to the declaration or the
>> commit message) to reflect this? (save space from .rodata, and this
>> being a noop for h.261, which doesn't matter that much)
>>
>>>> [PATCH 15/40] avcodec/ituh263enc: Make SVQ1+Snowenc stop calling
>>>> ff_h263_encode_init()
>>>>
>>>>> diff --git a/libavcodec/ituh263enc.c b/libavcodec/ituh263enc.c
>>>>> index 02da090ba4..8313b2c2c1 100644
>>>>> --- a/libavcodec/ituh263enc.c
>>>>> +++ b/libavcodec/ituh263enc.c
>>>>> @@ -65,6 +65,127 @@ static uint8_t  uni_h263_inter_rl_len [64*64*2*2];
>>>> [...]
>>>>> +static av_cold void h263_encode_init_static(void)
>>>>> +{
>>>>> +    static uint8_t rl_intra_table[2][2 * MAX_RUN + MAX_LEVEL + 3];
>>>>> +
>>>>> +    ff_rl_init(&ff_rl_intra_aic, rl_intra_table);
>>>>> +    ff_h263_init_rl_inter();
>>>>> +
>>>>> +    init_uni_h263_rl_tab(&ff_rl_intra_aic,  uni_h263_intra_aic_rl_len);
>>>>> +    init_uni_h263_rl_tab(&ff_h263_rl_inter, uni_h263_inter_rl_len);
>>>>> +
>>>>> +    init_mv_penalty_and_fcode();
>>>>> +}
>>>>> +
>>>>> +av_cold const uint8_t (*ff_h263_get_mv_penalty(void))[MAX_DMV*2+1]
>>>>> +{
>>>>> +    static AVOnce init_static_once = AV_ONCE_INIT;
>>>>> +
>>>>> +    ff_thread_once(&init_static_once, h263_encode_init_static);
>>>>> +
>>>>> +    return mv_penalty;
>>>>> +}
>>>>> +
>>>>
>>>> This approach kind of hides the rest of h263_encode_init_static() inside
>>>> ff_h263_get_mv_penalty(), so the name is a bit misleading. I'd expect
>>>> h263 to still call some init function and ff_h263_get_mv_penalty(), and
>>>> SVQ1 and Snow to only call ff_h263_get_mv_penalty(), which would only
>>>> take care of the mv_penalty table.
>>>>
>>>
>>> This would entail using another AVOnce etc. and this level of
>>> granularity is just not worth it.
>>
>> Ok.
>>
>>> The name is chosen for what it does for an outsider (i.e. from the
>>> perspective of svq1enc or snowenc, not the actual H.263 based encoders).
>>
>> I'm still not quite happy with the name and how it's used, but it's
>> good enough so I won't insist.
>>
>>>> [PATCH 20/40] avcodec/mpeg4video: Split ff_mpeg4_pred_dc()
>>>>
>>>>> diff --git a/libavcodec/mpeg4videoenc.c b/libavcodec/mpeg4videoenc.c
>>>>> index 64fb96a0cf..26f9b40ff7 100644
>>>>> --- a/libavcodec/mpeg4videoenc.c
>>>>> +++ b/libavcodec/mpeg4videoenc.c
>>>>> @@ -806,8 +806,14 @@ void ff_mpeg4_encode_mb(MpegEncContext *s,
>>>>> int16_t block[6][64],
>>>>>          const uint8_t *scan_table[6];
>>>>>          int i;
>>>>>
>>>>> -        for (i = 0; i < 6; i++)
>>>>> -            dc_diff[i] = ff_mpeg4_pred_dc(s, i, block[i][0], &dir[i],
>>>>> 1);
>>>>> +        for (int i = 0; i < 6; i++) {
>>>>
>>>> Redeclaring i inside for.
>>>
>>> There are other loops which use this i as loop variable. The shadowing
>>> is IMO less bad than keeping loops in their current form (with iterators
>>> that don't have loop-scope).
>>
>> Agreed. I also prefer scoped iterators.
> 
> I added a comment to #10 and modified #18 as described. I also changed
> #21 to protect the macro in parentheses and simplified the FF_RC_OFFSET
> macro in #31. Furthermore, there are now five more patches. All
> attached. https://github.com/mkver/FFmpeg/tree/mpegvideo_misc has been
> force-pushed.
> 
Will apply this patchset (with the issues pointed out by Ramiro fixed)
tomorrow unless there are objections.

- Andreas

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