[FFmpeg-devel] QSV Decoding - Issues and Regressions

[Ivan Uskov]

Hello Ronald,

Tuesday, August 4, 2015, 5:24:45 AM, you wrote:

RSB> Hi Ivan,

RSB> On Mon, Aug 3, 2015 at 4:50 PM, Ivan Uskov <ivan.uskov at nablet.com> wrote:

>> Hello Ronald,
>>
>> Monday, August 3, 2015, 11:37:22 PM, you wrote:
>>
>> RSB> On Mon, Aug 3, 2015 at 3:25 PM, Ivan Uskov <ivan.uskov at nablet.com>
>> wrote:
>>
>> >> By the way, about old implementation which "worked fine".
>> >> It just did drop all buffered frames at decoder re-init on new
>> >> sequence header, there is nice comment inside old qsvdec_h264.c:
>> >> /* TODO: flush delayed frames on reinit */
>>
>>
>> RSB> Each AVCodec has a flush function which should do this. So as you
>> RSB> suggested, you need a flushing state which means you will output "old"
>> RSB> frames while consuming new frames and caching them internally in some
>> way.
>> RSB> Then, when the decoder is flushed (either because flush was called, or
>> RSB> because all old cached frames have been returned), you can use all
>> queued
>> RSB> packets to reinit the hw and start outputing frames right away.
>> Thank you for suggestion but unfortunately AVCodec::flush is useless
>> for this issue. The AVCodec::flush intended to *drop* decoded frames
>> and reset decoder before seeking and it calls by module outside of decoder.
>> My task is keep all frames without losing and decoder initiates
>> "flushing" by itself. So it is different kind of "flush".


RSB> That's exactly what I said, I think you misunderstood.

RSB> Libav's decoder handles AVCodec.flush inside the size-change function.
But not qsv decoder ;-)
RSB> What I'm saying is to make it a state machine and move that code to
RSB> AVCodec.flush (if it's not there already), and otherwise (as part of your
RSB> state machine) buffer incoming patches after a size change until all
RSB> previous-sized packets have been processed.
I agree all about state machine. But still not sure that AVCodec.flush
(which is really a dummy yet) can be used during handling a frame size changing.
For the qsv decoder case the AVCodec.flush (called before seek)
should:
1. call MFXVideoDECODE_Reset() to reset decoder.
2. discard any buffered frames.
At the same time during handling a frame size changing it is
necessary:
1. defer re-init
2. deliver buffered output (no any discards) buffering input
3. when no frames at #2 destroy (not just reset) decoder, init new
instance.
For this sequence I do not see anything appropriate which can be taken
from AVCodec.flush, sorry.

RSB> Then, N new-sized frames later, you'll have N packets buffered, you can
RSB> input them into the decoder all at once and immediately start outputing
RSB> frames of the new size without additional delay except for the hw reinit.
Yes, it is exactly what will be implemented.
Thank you very much for suggestions.

-- 
Best regards,
 Ivan                            mailto:ivan.uskov at nablet.com