On Wed, 1 Feb 2017 21:32:21 +0000
Mark Thompson <[email protected]> wrote:
> For use by codec implementations which can allocate frames internally.
> ---
> Now with explicit prohibition on the user reading either field.
>
>
> doc/APIchanges | 3 +++
> libavcodec/avcodec.h | 23 ++++++++++++++++++++++-
> libavcodec/decode.c | 1 +
> libavcodec/utils.c | 1 +
> libavcodec/version.h | 2 +-
> 5 files changed, 28 insertions(+), 2 deletions(-)
>
> diff --git a/doc/APIchanges b/doc/APIchanges
> index c161618d9..694058574 100644
> --- a/doc/APIchanges
> +++ b/doc/APIchanges
> @@ -13,6 +13,9 @@ libavutil: 2015-08-28
>
> API changes, most recent first:
>
> +2017-xx-xx - xxxxxxx - lavc 57.34.0 - avcodec.h
> + Add AVCodecContext.hw_device_ctx.
> +
> 2017-02-01 - xxxxxxx - lavc - avcodec.h
> Deprecate AVCodecContext.refcounted_frames. This was useful for deprecated
> API only (avcodec_decode_video2/avcodec_decode_audio4). The new decode APIs
> diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
> index 8d8fa594a..5c3ce59b1 100644
> --- a/libavcodec/avcodec.h
> +++ b/libavcodec/avcodec.h
> @@ -3093,7 +3093,8 @@ typedef struct AVCodecContext {
> /**
> * A reference to the AVHWFramesContext describing the input (for
> encoding)
> * or output (decoding) frames. The reference is set by the caller and
> - * afterwards owned (and freed) by libavcodec.
> + * afterwards owned (and freed) by libavcodec - it should never be read
> by
> + * the caller after being set.
> *
> * - decoding: This field should be set by the caller from the
> get_format()
> * callback. The previous reference (if any) will always be
> @@ -3139,6 +3140,26 @@ typedef struct AVCodecContext {
> * (with the display dimensions being determined by the crop_* fields).
> */
> int apply_cropping;
> +
> + /**
> + * A reference to the AVHWDeviceContext describing the device which will
> + * be used by a hardware encoder/decoder. The reference is set by the
> + * caller and afterwards owned (and freed) by libavcodec - it should
> never
> + * be read by the caller after being set.
> + *
> + * This should only be used if either the codec device does not require
> + * hardware frames or any that are used are allocated internally by
> + * libavcodec. If the user wishes to supply any of the frames used as
> + * encoder input or decoder output then hw_frames_ctx should be used
> + * instead.
> + *
> + * - decoding: This field should be set by the caller from the
> get_format()
> + * callback. The previous reference (if any) will always be
> + * unreffed by libavcodec before the get_format() call.
> + *
> + * - encoding: This field should be set before avcodec_open2() is called.
> + */
> + AVBufferRef *hw_device_ctx;
I'm getting confused about what we want here. Wouldn't it be better to:
- make this field freely accessible, except read-only after
avcodec_open2() is called
- do not allow get_format to change the device, and require the user to
hw_frames_ctx instead
We have 2 use cases for this field:
- wrappers for "full" decoders - these generally can't change the
device, or it's not a use-case for which we need to make their
implementations more complex
- hwaccels - for these we provide the API for convenience, and
complexer interactions can be implemented by setting hw_frames_ctx
manually
For the hwaccel case, we could in particular provide an API which
returns codec- or profile-specific parameters like surface format and
surface count, which would make changing to hw_frames_ctx rather
unproblematic for a user.
But I don't know if I'm on the right way here.
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