From: Hans Verkuil <hverkuil@xs4all.nl>
To: Tomasz Figa <tfiga@chromium.org>
Cc: "Linux Media Mailing List" <linux-media@vger.kernel.org>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
"Mauro Carvalho Chehab" <mchehab@kernel.org>,
"Pawel Osciak" <posciak@chromium.org>,
"Alexandre Courbot" <acourbot@chromium.org>,
"Kamil Debski" <kamil@wypas.org>,
"Andrzej Hajda" <a.hajda@samsung.com>,
"Kyungmin Park" <kyungmin.park@samsung.com>,
"Jeongtae Park" <jtp.park@samsung.com>,
"Philipp Zabel" <p.zabel@pengutronix.de>,
"Tiffany Lin (林慧珊)" <tiffany.lin@mediatek.com>,
"Andrew-CT Chen (陳智迪)" <andrew-ct.chen@mediatek.com>,
"Stanimir Varbanov" <stanimir.varbanov@linaro.org>,
"Todor Tomov" <todor.tomov@linaro.org>,
"Nicolas Dufresne" <nicolas@ndufresne.ca>,
"Paul Kocialkowski" <paul.kocialkowski@bootlin.com>,
"Laurent Pinchart" <laurent.pinchart@ideasonboard.com>,
dave.stevenson@raspberrypi.org,
"Ezequiel Garcia" <ezequiel@collabora.com>,
"Maxime Jourdan" <maxi.jourdan@wanadoo.fr>
Subject: Re: [PATCH v3 2/2] media: docs-rst: Document memory-to-memory video encoder interface
Date: Mon, 8 Apr 2019 10:43:31 +0200 [thread overview]
Message-ID: <fded491f-8a25-3283-76c4-dee3dd56045e@xs4all.nl> (raw)
In-Reply-To: <CAAFQd5AqRzGehW6fN4P=_oVdPdH+bJQqKhxgP6zsu80p-74bXA@mail.gmail.com>
On 4/8/19 10:36 AM, Tomasz Figa wrote:
> On Mon, Mar 25, 2019 at 10:12 PM Hans Verkuil <hverkuil@xs4all.nl> wrote:
>>
>> Another comment found while creating compliance tests:
>>
>> On 1/24/19 11:04 AM, Tomasz Figa wrote:
>>> +Drain
>>> +=====
>>> +
>>> +To ensure that all the queued ``OUTPUT`` buffers have been processed and the
>>> +related ``CAPTURE`` buffers are given to the client, the client must follow the
>>> +drain sequence described below. After the drain sequence ends, the client has
>>> +received all encoded frames for all ``OUTPUT`` buffers queued before the
>>> +sequence was started.
>>> +
>>> +1. Begin the drain sequence by issuing :c:func:`VIDIOC_ENCODER_CMD`.
>>> +
>>> + * **Required fields:**
>>> +
>>> + ``cmd``
>>> + set to ``V4L2_ENC_CMD_STOP``
>>> +
>>> + ``flags``
>>> + set to 0
>>> +
>>> + ``pts``
>>> + set to 0
>>> +
>>> + .. warning::
>>> +
>>> + The sequence can be only initiated if both ``OUTPUT`` and ``CAPTURE``
>>> + queues are streaming. For compatibility reasons, the call to
>>> + :c:func:`VIDIOC_ENCODER_CMD` will not fail even if any of the queues is
>>> + not streaming, but at the same time it will not initiate the `Drain`
>>> + sequence and so the steps described below would not be applicable.
>>> +
>>> +2. Any ``OUTPUT`` buffers queued by the client before the
>>> + :c:func:`VIDIOC_ENCODER_CMD` was issued will be processed and encoded as
>>> + normal. The client must continue to handle both queues independently,
>>> + similarly to normal encode operation. This includes:
>>> +
>>> + * queuing and dequeuing ``CAPTURE`` buffers, until a buffer marked with the
>>> + ``V4L2_BUF_FLAG_LAST`` flag is dequeued,
>>> +
>>> + .. warning::
>>> +
>>> + The last buffer may be empty (with :c:type:`v4l2_buffer`
>>> + ``bytesused`` = 0) and in that case it must be ignored by the client,
>>> + as it does not contain an encoded frame.
>>> +
>>> + .. note::
>>> +
>>> + Any attempt to dequeue more buffers beyond the buffer marked with
>>> + ``V4L2_BUF_FLAG_LAST`` will result in a -EPIPE error from
>>> + :c:func:`VIDIOC_DQBUF`.
>>> +
>>> + * dequeuing processed ``OUTPUT`` buffers, until all the buffers queued
>>> + before the ``V4L2_ENC_CMD_STOP`` command are dequeued,
>>> +
>>> + * dequeuing the ``V4L2_EVENT_EOS`` event, if the client subscribes to it.
>>> +
>>> + .. note::
>>> +
>>> + For backwards compatibility, the encoder will signal a ``V4L2_EVENT_EOS``
>>> + event when the last frame has been decoded and all frames are ready to be
>>> + dequeued. It is deprecated behavior and the client must not rely on it.
>>> + The ``V4L2_BUF_FLAG_LAST`` buffer flag should be used instead.
>>> +
>>> +3. Once all ``OUTPUT`` buffers queued before the ``V4L2_ENC_CMD_STOP`` call are
>>> + dequeued and the last ``CAPTURE`` buffer is dequeued, the encoder is stopped
>>> + and it will accept, but not process any newly queued ``OUTPUT`` buffers
>>> + until the client issues any of the following operations:
>>> +
>>> + * ``V4L2_ENC_CMD_START`` - the encoder will not be reset and will resume
>>> + operation normally, with all the state from before the drain,
>>
>> I assume that calling CMD_START when *not* draining will succeed but does nothing.
>>
>> In other words: while draining is in progress START will return EBUSY. When draining
>> was finished, then START will resume the encoder. In all other cases it just returns
>> 0 since the encoder is really already started.
>>
>
> Yes, that was the intention and seems to be the closest to the
> behavior described in the existing documentation.
>
>>> +
>>> + * a pair of :c:func:`VIDIOC_STREAMOFF` and :c:func:`VIDIOC_STREAMON` on the
>>> + ``CAPTURE`` queue - the encoder will be reset (see the `Reset` sequence)
>>> + and then resume encoding,
>>> +
>>> + * a pair of :c:func:`VIDIOC_STREAMOFF` and :c:func:`VIDIOC_STREAMON` on the
>>> + ``OUTPUT`` queue - the encoder will resume operation normally, however any
>>> + source frames queued to the ``OUTPUT`` queue between ``V4L2_ENC_CMD_STOP``
>>> + and :c:func:`VIDIOC_STREAMOFF` will be discarded.
>>> +
>>> +.. note::
>>> +
>>> + Once the drain sequence is initiated, the client needs to drive it to
>>> + completion, as described by the steps above, unless it aborts the process by
>>> + issuing :c:func:`VIDIOC_STREAMOFF` on any of the ``OUTPUT`` or ``CAPTURE``
>>> + queues. The client is not allowed to issue ``V4L2_ENC_CMD_START`` or
>>> + ``V4L2_ENC_CMD_STOP`` again while the drain sequence is in progress and they
>>> + will fail with -EBUSY error code if attempted.
>>
>> I assume calling STOP again once the drain sequence completed just returns 0 and
>> doesn't do anything else (since we're already stopped).
>>
>
> Right.
>
>>> +
>>> + Although mandatory, the availability of encoder commands may be queried
>>> + using :c:func:`VIDIOC_TRY_ENCODER_CMD`.
>>
>> Some corner cases:
>>
>> 1) No buffers are queued on either vb2_queue, but STREAMON is called for both queues.
>> Now ENC_CMD_STOP is issued. What should happen?
>>
>> Proposal: the next time the applications queues a CAPTURE buffer it is returned
>> at once as an empty buffer with FLAG_LAST set.
>>
>
> SGTM. It's actually similar to a relatively common case where all
> CAPTURE buffers have been dequeued and the application has to refill
> the CAPTURE queue, but in the meantime a drain request needs to be
> issued.
>
>> 2) Both queues are streaming and buffers have been encoded, but currently no buffers
>> are queued on either vb2_queue. Now ENC_CMD_STOP is issued. What should happen?
>>
>> Proposal: the next time the applications queues a CAPTURE buffer it is returned
>> at once as an empty buffer with FLAG_LAST set. This is consistent with the
>> previous corner case.
>
> Agreed.
>
>>
>> 3) The CAPTURE queue contains buffers, the OUTPUT queue does not. Now ENC_CMD_STOP
>> is issued. What should happen?
>>
>> Proposal: the oldest CAPTURE buffer in the ready queue is returned as an empty
>> buffer with FLAG_LAST set.
>
> Generally agreed, but not sure if there is a reason to specifically
> refer to the oldest buffer. (I'm personally for keeping the queues
> ordered, though...)
Feel free to rephrase. Perhaps: "an empty CAPTURE buffer with FLAG_LAST set should be
queued up for userspace to signal that the encoder has stopped." Or something along
those lines.
Regards,
Hans
>
>>
>> 4) Both queues have queued buffers. ENC_CMD_STOP is issued to start the drain process.
>> Before the drain process completes STREAMOFF is called for either CAPTURE or
>> OUTPUT queue. What should happen?
>>
>> Proposal for STREAMOFF(CAPTURE): aborts the drain process and all CAPTURE buffers are
>> returned to userspace. If encoding is restarted, then any remaining OUTPUT buffers
>> will be used as input to the encoder.
>>
>
> Agreed.
>
>> Proposal for STREAMOFF(OUTPUT): the next capture buffer will be empty and have
>> FLAG_LAST set.
>
> Agreed.
>
>>
>> Some of this might have to be documented, but these corner cases should certainly be
>> tested by v4l2-compliance. Before I write those tests I'd like to know if you agree
>> with this.
>
> Agreed with just one minor comment. Thanks for checking with me!
>
> Best regards,
> Tomasz
>
next prev parent reply other threads:[~2019-04-08 8:43 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-24 10:04 [PATCH v3 0/2] Document memory-to-memory video codec interfaces Tomasz Figa
2019-01-24 10:04 ` [PATCH v3 1/2] media: docs-rst: Document memory-to-memory video decoder interface Tomasz Figa
2019-01-29 13:11 ` Hans Verkuil
2019-01-31 10:45 ` Hans Verkuil
2019-01-31 12:30 ` Hans Verkuil
2019-01-31 12:38 ` Hans Verkuil
2019-01-31 12:44 ` Philipp Zabel
2019-01-31 13:19 ` Hans Verkuil
2019-02-07 8:51 ` Tomasz Figa
2019-04-05 10:59 ` Philipp Zabel
2019-04-05 11:21 ` Hans Verkuil
2019-04-09 10:28 ` Tomasz Figa
2019-04-09 16:57 ` Philipp Zabel
2019-04-10 9:29 ` Hans Verkuil
2019-01-24 10:04 ` [PATCH v3 2/2] media: docs-rst: Document memory-to-memory video encoder interface Tomasz Figa
2019-01-29 13:52 ` Hans Verkuil
2019-03-14 13:57 ` Hans Verkuil
2019-04-05 8:12 ` Tomasz Figa
2019-04-05 10:03 ` Hans Verkuil
2019-04-08 9:23 ` Tomasz Figa
2019-04-08 11:11 ` Hans Verkuil
2019-04-09 9:35 ` Tomasz Figa
2019-04-10 8:50 ` Hans Verkuil
2019-04-10 16:05 ` Nicolas Dufresne
2019-04-15 8:56 ` Tomasz Figa
2019-04-15 12:30 ` Nicolas Dufresne
2019-04-05 5:53 ` Tomasz Figa
2019-04-05 7:09 ` Hans Verkuil
2019-03-21 10:10 ` Hans Verkuil
2019-04-08 6:59 ` Tomasz Figa
2019-04-08 7:43 ` Hans Verkuil
2019-04-08 9:35 ` Tomasz Figa
2019-03-25 13:12 ` Hans Verkuil
2019-03-25 16:33 ` Hans Verkuil
2019-04-08 8:40 ` Tomasz Figa
2019-04-08 8:36 ` Tomasz Figa
2019-04-08 8:43 ` Hans Verkuil [this message]
2019-04-09 7:11 ` Tomasz Figa
2019-04-09 9:37 ` Hans Verkuil
2019-04-09 9:43 ` Tomasz Figa
2019-05-22 8:43 ` Tomasz Figa
2019-05-22 8:51 ` Hans Verkuil
2019-05-22 14:16 ` Michael Tretter
2019-04-30 17:34 ` Michael Tretter
2019-05-14 8:12 ` Tomasz Figa
2019-05-16 8:37 ` Michael Tretter
2019-05-16 8:48 ` Tomasz Figa
2019-01-24 10:38 ` [PATCH v3 0/2] Document memory-to-memory video codec interfaces Hans Verkuil
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