[FFmpeg-devel] [PATCH 0/1] ffmpeg: Switch cuvid to generic hwaccel

[Timo Rothenpieler]

Am 17.06.2017 um 00:11 schrieb Philip Langdale:
> On Fri, 16 Jun 2017 21:53:22 +0200
> wm4 <nfxjfg at googlemail.com> wrote:
> 
>> On Fri, 16 Jun 2017 20:31:14 +0200
>> Timo Rothenpieler <timo at rothenpieler.org> wrote:
>>
>>> Am 16.06.2017 um 16:41 schrieb Philip Langdale:
>>>> This is mechanically simple, but does the fact that additional
>>>> command line arguments have to be used to get the same results
>>>> count as a compatibility break? Do we need to fix that before we
>>>> can actually make this change?
>>>
>>> I'd consider that as a breaking change, even though things don't
>>> "break", it results in unexpected behavior that is not obvious.
>>
>> Probably, but it's also slightly saner in general if you consider that
>> a user could add video filters. Currently, hwaccel filters and normal
>> filters are completely different beasts, so the user needs to be aware
>> of the difference, and select the appropriate mode. So depending on
>> whether you output hw surfaces by default, you'll break hw filters or
>> sw filters by default. Making sure sw filters work by default seems
>> like the better choice.
>>
>> But yes, maybe we could rename the hwaccel just so that users of the
>> old hwaccel become aware of the change. You could even keep the old
>> hwaccel name, and make it somehow override the -hwaccel_output_format
>> option and print a warning, in case you care enough for compatibility
>> in this case.
> 
> We could use it as an opportunity to rename it to 'cuda' which is more
> accurate.
> 
> Keeping the old specialised code for 'cuvid' would also ensure
> compatibility :-)

One thing to keep in mind is that cuvid is vastly different from other 
hwaccels.
While for example for vaapi, specifying -hwaccel vaapi makes the h264 
decoder use vaapi. But for cuvid, the h264_cuvid decoder always uses 
hardware, and the -hwaccel cuvid flag is essentially used to switch its 
output mode to cuda frames.
With the new approach, there is no apparent difference from using cuvid 
with or without -hwaccel cuvid.
That situation would seem kinda weird and confusing to me.