On Fri, Sep 20, 2024 at 1:24 AM Carlos Ruiz <carlos.r.do...@gmail.com> wrote:
>
> Hi!
>
> This is my first contribution to the project so please excuse any bad
> etiquette, I tried to read all the FAQs before posting. Would love to start
> by thanking everyone for such an amazing framework you've built!
>
> Anyway, here's my proposed patch to support video resizing when using NVDEC
> hwaccel to decode hevc video (I could look into a similar patch for h264,
> av1, etc if this looks useful). There's a bit more context/explanation in
> the commit description in the patch, but please let me know if the use case
> isn't clear.
>
We don't really leverage these extra functions of NVDEC because it
breaks many assumptions about hwaccels, which are meant to be exact
decoders.
If anything, just fudging the width/height is certainly an API
violation and will likely not be possible as it breaks many
assumptions in the code otherwise, see below.
> ---
> libavcodec/hevc/hevcdec.c | 8 ++++++--
> libavcodec/nvdec.c | 21 +++++++++++++++++----
> 2 files changed, 23 insertions(+), 6 deletions(-)
>
> diff --git a/libavcodec/hevc/hevcdec.c b/libavcodec/hevc/hevcdec.c
> index d915d74d22..d63fc5875f 100644
> --- a/libavcodec/hevc/hevcdec.c
> +++ b/libavcodec/hevc/hevcdec.c
> @@ -351,8 +351,12 @@ static void export_stream_params(HEVCContext *s, const
> HEVCSPS *sps)
> avctx->pix_fmt = sps->pix_fmt;
> avctx->coded_width = sps->width;
> avctx->coded_height = sps->height;
> - avctx->width = sps->width - ow->left_offset -
> ow->right_offset;
> - avctx->height = sps->height - ow->top_offset -
> ow->bottom_offset;
> + if (avctx->width <= 0 || avctx->height <= 0) {
> + avctx->width = sps->width;
> + avctx->height = sps->height;
> + }
> + avctx->width = avctx->width - ow->left_offset -
> ow->right_offset;
> + avctx->height = avctx->height - ow->top_offset -
> ow->bottom_offset;
You cannot do that here. The frame size can change mid-stream, and
this would suppress any such change.
Additionally, if this code runs more then once, then the offset is
applied repeatedly without actually resetting width/height.
- Hendrik
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