On Wed, 2020-09-02 at 20:37 +0100, Mark Thompson wrote: > > > I still don't see the full picture. What I am looking for at the > > > first > > > place is how maintainers and architects envision hwaccel to work > > > in > > > general. Basically, there are few ways to specify the device (- > > > hwaccel, > > > -init_hw_device, -filter_hw_device), questions are: > > > 1. What's scope of applicability of each option w/ explanation > > > why > > > each > > > of the option is actually needed (as one of the examples: why - > > > filter_hw_device is needed and why -init_hw_device can't be used > > > instead? > > -init_hw_device is a global option which defines a device and adds it > to the list in ffmpeg; you can have as many of these as you like. > > When setting up a codec which might be able to use a device it tries > to match against that list, unless you have an explicit > -hwaccel_device option for that input. If you do, then it looks for > the device with that name. > > To maintain compatibility with old command-lines where > -hwaccel_device took a string interpreted by special code for each > API in ffmpeg (now removed), if it doesn't find a device with the > given name then it will try to use it to create a new one. > > (So "-hwaccel foo -hwaccel_device bar" when "bar" hasn't been > previously defined ends up with the effect of "-init_hw_device > foo=quux:bar -hwaccel foo -hwaccel_device quux".) > > This doesn't apply to the libmfx decoders, because they have their > own ad-hoc code. Getting rid of that so they work in the same way as > everything else would be a good thing. > > -filter_hw_device selects a device from the list to use while > filtering (e.g. by hwupload). > > If there is exactly one device in the list when making a filter graph > then it will use that, but if there are multiple then it has no way > to guess which one you meant so the option is needed.
Hm. I am pretty sure I saw the case when for one of qsv pipelines when I was forced to add -filter_hw_device to make things workable thought there was only one device specified. That's why I was specially asking about the filter option. This was long ago however and I don't remember what exactly I ran. Besides, this might have messed up with the fact that qsv decoder don't work with -init_hw_device... I think I need to pay attention on this long past use case after we will deal with the decoder story... If I will note some strange behavior, I'll post update. > > > 2. Since there are few methods how component can get a device: > > > what's > > > the priority order? (for example, if device can be deducted from > > > incoming frames, is there a way to override it w/ some command > > > line > > > options?) > > Devices from incoming frames have to win, because they are stored on > that device - it doesn't make sense to select a different device at > that point (you would need a separate download/upload or mapping step > to do that). > > - Mark Thank you, Mark. Your description greatly helps and aligns with expectations I have. > _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
