Well this does make sense.
If only one type of hardware device is in use, then `-init_hw_device` will
suffice. However, if we use hardware filters with different device types, such
as OpenCL, and we want to switch to a VideoToolbox filter later in the chain,
we will have a issue. Since there is no `hwmap` between OpenCL and
VideoToolbox, we need to perform a `hwdownload` followed by a `hwupload`. If
the `derive_device` option cannot be used with `hwupload` due to
`device_derive` not being implemented, the filter will struggle to find the
correct device for uploading. It may attempt to upload to the OpenCL device
without `device_derive` set if it comes after an OpenCL filter.
> On Feb 23, 2024, at 03:28, Mark Thompson <s...@jkqxz.net> wrote:
>
> On 22/02/2024 18:46, gnattu via ffmpeg-devel wrote:
>> There is no device context to be setup, nor devices to be
>> selected with VideoToolbox. Just a simple return would allow
>> us to use derived device in filters like
>> `hwupload=derive_device=videotoolbox`
>> Signed-off-by: Gnattu OC <gnatt...@me.com>
>> ---
>> libavutil/hwcontext_videotoolbox.c | 9 +++++++++
>> 1 file changed, 9 insertions(+)
>> diff --git a/libavutil/hwcontext_videotoolbox.c
>> b/libavutil/hwcontext_videotoolbox.c
>> index fe469dc161..d13199eca7 100644
>> --- a/libavutil/hwcontext_videotoolbox.c
>> +++ b/libavutil/hwcontext_videotoolbox.c
>> @@ -759,6 +759,14 @@ static int vt_device_create(AVHWDeviceContext *ctx,
>> const char *device,
>> return 0;
>> }
>> +static int vt_device_derive(AVHWDeviceContext *device_ctx,
>> + AVHWDeviceContext *src_ctx, AVDictionary *opts,
>> + int flags)
>> +{
>> + // There is no context to be setup with VT, just return.
>> + return 0;
>> +}
>> +
>> const HWContextType ff_hwcontext_type_videotoolbox = {
>> .type = AV_HWDEVICE_TYPE_VIDEOTOOLBOX,
>> .name = "videotoolbox",
>> @@ -766,6 +774,7 @@ const HWContextType ff_hwcontext_type_videotoolbox = {
>> .frames_priv_size = sizeof(VTFramesContext),
>> .device_create = vt_device_create,
>> + .device_derive = vt_device_derive,
>> .frames_hwctx_size = sizeof(AVVTFramesContext),
>> .frames_init = vt_frames_init,
>> .frames_get_buffer = vt_get_buffer,
>
> This derivation behaviour doesn't make any sense inside libavutil. Features
> which are only for the ffmpeg utility should be implemented inside the ffmpeg
> utility.
>
> (Also, try -init_hw_device.)
>
> Thanks,
>
> - Mark
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