[FFmpeg-devel] [PATCH v2] cbs_h2645: Implement replace-PS with a table rather than many functions

[James Almer]

On 2/16/2021 12:16 PM, Nuo Mi wrote:
> On Tue, Feb 16, 2021 at 7:20 AM Mark Thompson <sw at jkqxz.net> wrote:
> 
>> While this is mode source code, it generates less binary code and can be
>> more cleanly extended to H.266.
>> ---
>> On 14/02/2021 19:45, Andreas Rheinhardt wrote:
>>> Nuo Mi:
>>>> From: Mark Thompson <sw at jkqxz.net>
>>
>> Hi Andreas & Mark,
> thanks for the suggestion.
> 
> Hi Mark,
> vvc's xps does not need active_offset.

The change you suggest here is not needed to handle this, as you only 
need to define a H266_PS_TYPE macro that does not set .active_offset 
(When using designated initializers, fields that are not set will be 
zeroed).
But at the end of the day, it's a cosmetic choice, so whatever you two 
prefer is fine.

 > vvc's picture header does not need id_offset. see [1], [2] for details

This one most likely needs the change you suggested below, though.

> How about we change the patch like this:
> 
> $git diff
> diff --git a/libavcodec/cbs_h2645.c b/libavcodec/cbs_h2645.c
> index 6c44e781fa..57c419aa05 100644
> --- a/libavcodec/cbs_h2645.c
> +++ b/libavcodec/cbs_h2645.c
> @@ -690,20 +690,24 @@ static int cbs_h2645_replace_ps(CodedBitstreamContext
> *ctx,
>           size_t active_offset;
>       } PSType;
> 
> -#define H2645_PS_TYPE(codec, nal, cname, uname, count, id_name,
> active_field) { \
> +#define H26456_PS_TYPE(codec, nal, cname, uname, count, id_off,
> active_off) { \
>           .codec_id         = AV_CODEC_ID_ ## codec, \
>           .nal_unit_type    = nal, \
>           .name             = #cname, \
>           .id_count         = count, \
> -        .id_offset        = offsetof(codec ## Raw ## cname, \
> -                                     id_name ## _parameter_set_id), \
> +        .id_offset        = id_off, \
>           .ref_array_offset = offsetof(CodedBitstream ## codec ## Context, \
>                                        uname ## _ref), \
>           .ptr_array_offset = offsetof(CodedBitstream ## codec ## Context, \
>                                        uname), \
> -        .active_offset    = offsetof(CodedBitstream ## codec ## Context, \
> -                                     active_field), \
> +        .active_offset    = active_off, \
>       }
> +
> +#define H2645_PS_TYPE(codec, nal, cname, uname, count, id_name,
> active_field) \
> +        H26456_PS_TYPE(codec, nal, cname, uname, count, \
> +            offsetof(codec ## Raw ## cname, id_name ## _parameter_set_id),
> \
> +            offsetof(CodedBitstream ## codec ## Context, active_field))
> +
>   #define H264_PS_TYPE(cname, uname, id_name) \
>       H2645_PS_TYPE(H264, H264_NAL_ ## cname, cname, uname, \
>                     H264_MAX_ ## cname ## _COUNT, \
> @@ -724,7 +728,7 @@ static int cbs_h2645_replace_ps(CodedBitstreamContext
> *ctx,
>       const PSType *ps_type;
>       AVBufferRef **ref_array;
>       void **ptr_array;
> -    int err, id, i;
> +    int err, id = 0, i;
> 
>       ps_type = NULL;
>       for (i = 0; i < FF_ARRAY_ELEMS(ps_types); i++) {
> @@ -736,12 +740,14 @@ static int cbs_h2645_replace_ps(CodedBitstreamContext
> *ctx,
>       }
>       av_assert0(ps_type);
> 
> -    id = *((uint8_t*)unit->content + ps_type->id_offset);
> +    if (ps_type->id_offset) {
> +        id = *((uint8_t*)unit->content + ps_type->id_offset);
> 
> -    if (id >= ps_type->id_count) {
> -        av_log(ctx->log_ctx, AV_LOG_ERROR, "Invalid %s id: %d.\n",
> -               ps_type->name, id);
> -        return AVERROR_INVALIDDATA;
> +        if (id >= ps_type->id_count) {
> +            av_log(ctx->log_ctx, AV_LOG_ERROR, "Invalid %s id: %d.\n",
> +                ps_type->name, id);
> +            return AVERROR_INVALIDDATA;
> +        }
>       }
> 
>       err = ff_cbs_make_unit_refcounted(ctx, unit);
> 
> 
> [1]:
> https://patchwork.ffmpeg.org/project/ffmpeg/patch/20210211143611.5663-5-nuomi2021@gmail.com/
> [2] h266_ps_types in
> https://patchwork.ffmpeg.org/project/ffmpeg/patch/20210211143611.5663-6-nuomi2021@gmail.com/
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