Re: [FFmpeg-devel] [PATCH 2/4 v6] avformat: add a Tile Grid stream group type

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

James Almer:
> On 1/31/2024 3:08 PM, Andreas Rheinhardt wrote:
>> James Almer:
>>> This will be used to support tiled image formats like HEIF.
>>>
>>> Signed-off-by: James Almer<jamrial@gmail.com>
>>> ---
>>>   libavformat/avformat.c |   5 +++
>>>   libavformat/avformat.h | 100 +++++++++++++++++++++++++++++++++++++++++
>>>   libavformat/dump.c     |  29 ++++++++++++
>>>   libavformat/options.c  |  32 +++++++++++++
>>>   4 files changed, 166 insertions(+)
>>>
>>> diff --git a/libavformat/avformat.c b/libavformat/avformat.c
>>> index 8e8c6fbe55..32ef440207 100644
>>> --- a/libavformat/avformat.c
>>> +++ b/libavformat/avformat.c
>>> @@ -100,6 +100,11 @@ void ff_free_stream_group(AVStreamGroup **pstg)
>>>          
>>> av_iamf_mix_presentation_free(&stg->params.iamf_mix_presentation);
>>>           break;
>>>       }
>>> +    case AV_STREAM_GROUP_PARAMS_TILE_GRID:
>>> +        av_opt_free(stg->params.tile_grid);
>>> +        av_freep(&stg->params.tile_grid->offsets);
>>> +        av_freep(&stg->params.tile_grid);
>>> +        break;
>>>       default:
>>>           break;
>>>       }
>>> diff --git a/libavformat/avformat.h b/libavformat/avformat.h
>>> index 5d0fe82250..6577f13ef1 100644
>>> --- a/libavformat/avformat.h
>>> +++ b/libavformat/avformat.h
>>> @@ -1018,10 +1018,109 @@ typedef struct AVStream {
>>>       int pts_wrap_bits;
>>>   } AVStream;
>>>   +/**
>>> + * AVStreamGroupTileGrid holds information on how to combine several
>>> + * independent images on a single grid for presentation. None of the
>>> tiles may
>>> + * overlap inside the grid.
>>> + *
>>> + * The following is an example of a simple grid with 3 rows and 4
>>> columns:
>>> + *
>>> + * +---+---+---+---+
>>> + * | 0 | 1 | 2 | 3 |
>>> + * +---+---+---+---+
>>> + * | 4 | 5 | 6 | 7 |
>>> + * +---+---+---+---+
>>> + * | 8 | 9 |10 |11 |
>>> + * +---+---+---+---+
>>> + *
>>> + * Assuming all tiles have a dimension of 512x512, the
>>> + * @ref AVStreamGroupTileGrid.offsets "offset" of the topleft pixel of
>>> + * the first @ref AVStreamGroup.streams "stream" in the group is
>>> "0,0", the
>>> + * @ref AVStreamGroupTileGrid.offsets "offset" of the topleft pixel of
>>> + * the second @ref AVStreamGroup.streams "stream" in the group is
>>> "512,0", the
>>> + * @ref AVStreamGroupTileGrid.offsets "offset" of the topleft pixel of
>>> + * the fifth @ref AVStreamGroup.streams "stream" in the group is
>>> "0,512", the
>>> + * @ref AVStreamGroupTileGrid.offsets "offset", of the topleft pixel of
>>> + * the sixth @ref AVStreamGroup.streams "stream" in the group is
>>> "512,512",
>>> + * etc.
>>> + *
>>> + * sizeof(AVStreamGroupTileGrid) is not a part of the ABI. No new
>>> fields may be
>>> + * added to this struct without a major version bump.
>> This is inconsistent. I think you mean that sizeof is part of the ABI.
> 
> No? It's not a part of the ABI because AVStreamGroupTileGrid must not be
> ever used on stack, or allocated by anything other than AVStreamGroup.
> That way we can add fields to it without waiting for a major bump.

"No new fields may be added to this struct without a major version bump"

- Andreas

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