Re: [FFmpeg-devel] [PATCH v2] avutil/frame: add av_frame_replace

[Anton Khirnov <anton@khirnov.net>]

Quoting James Almer (2022-06-05 19:44:58)
> +
> +    /* duplicate the frame data if it's not refcounted */
> +    if (!src->buf[0]) {
> +        for (int i = 0; i < FF_ARRAY_ELEMS(dst->buf); i++)
> +            av_buffer_unref(&dst->buf[i]);
> +        for (int i = 0; i < dst->nb_extended_buf; i++)
> +            av_buffer_unref(&dst->extended_buf[i]);
> +        av_freep(&dst->extended_buf);
> +
> +        memset(dst->data, 0, sizeof(dst->data));
> +        if (dst->extended_data != dst->data)
> +            av_freep(&dst->extended_data);
> +
> +        ret = av_frame_get_buffer(dst, 0);
> +        if (ret < 0)
> +            goto fail;
> +
> +        ret = av_frame_copy(dst, src);
> +        if (ret < 0)
> +            goto fail;
> +
> +        ret = av_buffer_replace(&dst->hw_frames_ctx, src->hw_frames_ctx);
> +        if (ret < 0)
> +            goto fail;

This looks suspicious, since we just allocated normal buffers for dst.
Also, can't t this whole block be replaced by just

if (!src->buf[0]) {
    av_frame_unref(dst);
    return av_frame_ref(dst, src);
}

at the beginning of this function?

> +    if (src->extended_data != src->data) {
> +        int ch = src->ch_layout.nb_channels;
> +
> +#if FF_API_OLD_CHANNEL_LAYOUT
> +FF_DISABLE_DEPRECATION_WARNINGS
> +        if (!ch) {
> +            ch = src->channels;
> +            CHECK_CHANNELS_CONSISTENCY(src);
> +        }
> +FF_ENABLE_DEPRECATION_WARNINGS
> +#endif
> +        if (!ch) {
> +            ret = AVERROR(EINVAL);
> +            goto fail;
> +        }
> +
> +        dst->extended_data = av_malloc_array(sizeof(*dst->extended_data), ch);
> +        if (!dst->extended_data) {
> +            ret = AVERROR(ENOMEM);
> +            goto fail;
> +        }
> +        memcpy(dst->extended_data, src->extended_data, sizeof(*src->extended_data) * ch);

nit: av_memdup()?

> +    } else
> +        dst->extended_data = dst->data;
> +
> +    memcpy(dst->data,     src->data,     sizeof(src->data));
> +    memcpy(dst->linesize, src->linesize, sizeof(src->linesize));
> +
> +    return 0;
> +
> +fail:
> +    av_frame_unref(dst);
> +    return ret;
> +}
> +
>  AVFrame *av_frame_clone(const AVFrame *src)
>  {
>      AVFrame *ret = av_frame_alloc();
> diff --git a/libavutil/frame.h b/libavutil/frame.h
> index 33fac2054c..e5c10e2b66 100644
> --- a/libavutil/frame.h
> +++ b/libavutil/frame.h
> @@ -752,6 +752,19 @@ void av_frame_free(AVFrame **frame);
>   */
>  int av_frame_ref(AVFrame *dst, const AVFrame *src);
>  
> +/**
> + * Ensure the destination frame refers to the same data described by the source
> + * frame by creating a new reference for each AVBufferRef from src if they
> + * differ from those in dst, or if src is not reference counted, by allocating
> + * new buffers and copying data.
> + *
> + * Frame properties on dst will be replaced by those from src.
> + *
> + * @return 0 on success, a negative AVERROR on error. On error, dst is
> + *         unreferenced.
> + */
> +int av_frame_replace(AVFrame *dst, const AVFrame *src);

An important property of av_buffer_replace() is that it's equivalent to
av_buffer_unref(dst) when src is NULL. It would probably be desirable
for av_frame_replace() to work the same way - currently it will try to
call av_frame_get_buffer() with invalid parameters and fail.

-- 
Anton Khirnov
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