Re: [FFmpeg-devel] [PATCH] avutil/frame: use bitfields for some boolean and enum fields

[Lynne <dev@lynne.ee>]

Apr 17, 2023, 16:40 by jamrial@gmail.com:

> Should reduce the size of AVFrame in the next major bump without changing the API.
>
> Suggested-by: Anton Khirnov <anton@khirnov.net>
> Signed-off-by: James Almer <jamrial@gmail.com>
> ---
> This supersedes "avutil/frame: add new interlaced and top_field_first flags"
> and "avutil/frame: add a keyframe flag to AVFrame".
>
>  libavutil/frame.h   | 56 +++++++++++++++++++++++++++++++++++++++++++++
>  libavutil/version.h |  1 +
>  2 files changed, 57 insertions(+)
>
> diff --git a/libavutil/frame.h b/libavutil/frame.h
> index f85d630c5c..c26067f383 100644
> --- a/libavutil/frame.h
> +++ b/libavutil/frame.h
> @@ -416,6 +416,7 @@ typedef struct AVFrame {
>  */
>  int format;
>  
> +#if FF_API_BITFIELDS
>  /**
>  * 1 -> keyframe, 0-> not
>  */
> @@ -425,6 +426,57 @@ typedef struct AVFrame {
>  * Picture type of the frame.
>  */
>  enum AVPictureType pict_type;
> +#else
> +    /**
> +     * 1 -> keyframe, 0-> not
> +     */
> +    unsigned int key_frame: 1;
> +
> +    /**
> +     * The content of the picture is interlaced.
> +     */
> +    unsigned int interlaced_frame: 1;
> +
> +    /**
> +     * If the content is interlaced, is top field displayed first.
> +     */
> +    unsigned int top_field_first: 1;
> +
> +    /**
> +     * Tell user application that palette has changed from previous frame.
> +     */
> +    unsigned int palette_has_changed: 1;
> +
> +    /**
> +     * Reserved. Must not be touched.
> +     */
> +    unsigned int reserved_bitfield: (sizeof(unsigned int) * 8) - 9;
> +
> +    /**
> +     * MPEG vs JPEG YUV range.
> +     * - encoding: Set by user
> +     * - decoding: Set by libavcodec
> +     */
> +    enum AVColorRange color_range: 2;
> +
> +    enum AVChromaLocation chroma_location: 3;
>

Definitely disagree on all non-8bit field limits.
The reserved_bitfield is especially ugly.
A few wasted bits wouldn't affect much, we don't even support building on 6502s.
Use bools, or limit them to 8bits so we can use bools when we bump?
The rest can be limited to 8bits.
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