media: videobuf2: Fails to scale H264 1080p video on 1920x1080 screen

media: videobuf2: Fails to scale H264 1080p video on 1920x1080 screen

[trung1.dothanh]

Hello,

I am trying to play video with Gstreamer  on a fullHD monitor. The board I’m using is Apalis iMX6.
Playing video works great with v4l2h264dec:

	gst-launch-1.0 filesrc location=1080.mkv ! matroskademux ! h264parse \
                          ! v4l2h264dec capture-io-mode=dmabuf \
                          ! kmssink

However, it fails to scale video to 720p with v4l2convert:

	gst-launch-1.0 filesrc location=1080.mkv ! matroskademux ! h264parse \
                          ! v4l2h264dec capture-io-mode=dmabuf \
                          ! v4l2convert output-io-mode=dmabuf-import \
                          ! video/x-raw,width=1280,height=720 \
                          ! kmssink

Added some debugs and I found that it failed at 'drivers/media/common/videobuf2/videobuf2-v4l2.c:__verify_length()'.

	length = (b->memory == VB2_MEMORY_USERPTR)
		? b->length : vb->planes[0].length;
	if (b->bytesused > length)
		return -EINVAL;

The “b->byteused” is 4177920 (= 2 x 1920 x 1088), while plane length is just 4147200 (= 2 x 1920 x 1080).
The actual frame size of H264 video is 1920x1088, so I added  a bypass for this case and video can be scaled,
but that may not a correct way to fix this problem.

Is this a bug or I need to do extra steps before scale video?

Packages version in my environment are:
* Kernel: 5.10.19
* Gstreamer: 1.18.4

Thank you,
Trung

Re: media: videobuf2: Fails to scale H264 1080p video on 1920x1080 screen

[Nicolas Dufresne]

Le vendredi 20 août 2021 à 08:55 +0000, trung1.dothanh@toshiba.co.jp a écrit :
> Hello,
> 
> I am trying to play video with Gstreamer  on a fullHD monitor. The board I’m using is Apalis iMX6.
> Playing video works great with v4l2h264dec:
> 
> 	gst-launch-1.0 filesrc location=1080.mkv ! matroskademux ! h264parse \
>                           ! v4l2h264dec capture-io-mode=dmabuf \
>                           ! kmssink
> 
> However, it fails to scale video to 720p with v4l2convert:
> 
> 	gst-launch-1.0 filesrc location=1080.mkv ! matroskademux ! h264parse \
>                           ! v4l2h264dec capture-io-mode=dmabuf \
>                           ! v4l2convert output-io-mode=dmabuf-import \
>                           ! video/x-raw,width=1280,height=720 \
>                           ! kmssink
> 
> Added some debugs and I found that it failed at 'drivers/media/common/videobuf2/videobuf2-v4l2.c:__verify_length()'.
> 
> 	length = (b->memory == VB2_MEMORY_USERPTR)

Wrong snippet ? You are using VB2_MEMORY_DMABUF according to your GStreamer
pipeline.

> 		? b->length : vb->planes[0].length;
> 	if (b->bytesused > length)
> 		return -EINVAL;
> 
> The “b->byteused” is 4177920 (= 2 x 1920 x 1088), while plane length is just 4147200 (= 2 x 1920 x 1080).
> The actual frame size of H264 video is 1920x1088, so I added  a bypass for this case and video can be scaled,
> but that may not a correct way to fix this problem.
> 
> Is this a bug or I need to do extra steps before scale video?

I'm not fully certain of what has gone wrong, since this call was added
(1.18.0), this code path is supposed to work:

https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/-/blob/master/sys/v4l2/gstv4l2transform.c#L905

GStreamer will update the driver FMT to padded width/height before calling
streamon and S_SELECTION is used to tell the scaler which part is to be used in
the scaling process.

> 
> Packages version in my environment are:
> * Kernel: 5.10.19
> * Gstreamer: 1.18.4
> 
> Thank you,
> Trung
> 

RE: media: videobuf2: Fails to scale H264 1080p video on 1920x1080 screen

[trung1.dothanh]

Thank you for your reply. Sorry for not make it clear.

> 	length = (b->memory == VB2_MEMORY_USERPTR)
>		? b->length : vb->planes[0].length;

> Wrong snippet ? You are using VB2_MEMORY_DMABUF according to your GStreamer pipeline.

That's right. "b->memory" is VB2_MEMORY_DMABUF, then "length" is " vb->planes[0].length",
which has value 4147200 (= 2 x 1920 x 1080).
My issue is the decoded frame of H264 video is 1920x1088, while plane is only 1920x1080,
and that makes __verify_length return '-EINVAL'.
I am wondering if this function should have a special check for the case like this:
fullHD H264 frame (1920x1088) with fullHD screen (1920x1080).

 > I'm not fully certain of what has gone wrong, since this call was added (1.18.0), this code path is supposed to work:

> https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/-/blob/master/sys/v4l2/gstv4l2transform.c#L905

> GStreamer will update the driver FMT to padded width/height before calling streamon and S_SELECTION is used to tell the scaler which part is to be used in the scaling process.

Thank you. I will check this code to see what I'm missing.

Thanks,
Trung

-----Original Message-----
From: Nicolas Dufresne [mailto:nicolas@ndufresne.ca] 
Sent: Friday, August 20, 2021 9:36 PM
To: do thanh trung(ＴＳＤＶ Ｅｎｇ　１) <trung1.dothanh@toshiba.co.jp>; linux-media@vger.kernel.org
Subject: Re: media: videobuf2: Fails to scale H264 1080p video on 1920x1080 screen

Le vendredi 20 août 2021 à 08:55 +0000, trung1.dothanh@toshiba.co.jp a écrit :
> Hello,
> 
> I am trying to play video with Gstreamer  on a fullHD monitor. The board I’m using is Apalis iMX6.
> Playing video works great with v4l2h264dec:
> 
> 	gst-launch-1.0 filesrc location=1080.mkv ! matroskademux ! h264parse \
>                           ! v4l2h264dec capture-io-mode=dmabuf \
>                           ! kmssink
> 
> However, it fails to scale video to 720p with v4l2convert:
> 
> 	gst-launch-1.0 filesrc location=1080.mkv ! matroskademux ! h264parse \
>                           ! v4l2h264dec capture-io-mode=dmabuf \
>                           ! v4l2convert output-io-mode=dmabuf-import \
>                           ! video/x-raw,width=1280,height=720 \
>                           ! kmssink
> 
> Added some debugs and I found that it failed at 'drivers/media/common/videobuf2/videobuf2-v4l2.c:__verify_length()'.
> 
> 	length = (b->memory == VB2_MEMORY_USERPTR)

Wrong snippet ? You are using VB2_MEMORY_DMABUF according to your GStreamer pipeline.

> 		? b->length : vb->planes[0].length;
> 	if (b->bytesused > length)
> 		return -EINVAL;
> 
> The “b->byteused” is 4177920 (= 2 x 1920 x 1088), while plane length is just w
> The actual frame size of H264 video is 1920x1088, so I added  a bypass 
> for this case and video can be scaled, but that may not a correct way to fix this problem.
> 
> Is this a bug or I need to do extra steps before scale video?

I'm not fully certain of what has gone wrong, since this call was added (1.18.0), this code path is supposed to work:

https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/-/blob/master/sys/v4l2/gstv4l2transform.c#L905

GStreamer will update the driver FMT to padded width/height before calling streamon and S_SELECTION is used to tell the scaler which part is to be used in the scaling process.

> 
> Packages version in my environment are:
> * Kernel: 5.10.19
> * Gstreamer: 1.18.4
> 
> Thank you,
> Trung
>