* Using v4l2 API example as-is for video capture
@ 2016-01-08 6:25 Ran Shalit
2016-01-08 14:03 ` Ran Shalit
2016-01-11 11:29 ` Hans Verkuil
0 siblings, 2 replies; 4+ messages in thread
From: Ran Shalit @ 2016-01-08 6:25 UTC (permalink / raw)
To: linux-media
Hello,
I am trying to use v4l2 example from API documentation:
inhttp://linuxtv.org/downloads/v4l-dvb-apis/capture-example.html .
As a start, I wanted to first try uding it with vivid (virtual device driver).
I found excelent vivid documentation in the kernel, which is very helpful:
https://www.kernel.org/doc/Documentation/video4linux/vivid.txt
But on trying to use the example as-is for capturing video frames into
file, and playing the file, I encounter difficulties.
I tried the example as-is, and then tried several resolution,
pixelformat, different inputs, but it always result with video with a
sync problems ( the test bars of the video are keep moving in the
horizontal axis, or the text is changing its location for one frame to
the next).
I compiled the v4l2 API example AS-IS from:
http://linuxtv.org/downloads/v4l-dvb-apis/capture-example.html with
minor modification in the --force part of the example (I also tried
the example as is without modifications but it did not help), so that
I choose hd input , and 1920x1080 resolution, V4L2_PIX_FMT_YUV420
(also tried V4L2_PIX_FMT_YUV422P) , progressive.
if (force_format) {
input = 3; // <<-- HD input device
if (-1==xioctl(fd,VIDIOC_S_INPUT,&input))
{
errno_exit("VIDIOC_S_INPUT");
}
fmt.fmt.pix.width = 1920;
fmt.fmt.pix.height = 1080;
fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUV420; // <<-
tried also V4L2_PIX_FMT_YUV422P
fmt.fmt.pix.field = V4L2_FIELD_NONE; // <- trying to
capture progressive
if (-1 == xioctl(fd, VIDIOC_S_FMT, &fmt))
errno_exit("VIDIOC_S_FMT");
} else {
I run the application with (the compiled code using pixelformat =
V4L2_PIX_FMT_YUV420 trial ):
./v4l2_example -f -o -c 10 > cap_yuv420p.yuv
And (the compiled code using pixelformat = V4L2_PIX_FMT_YUV422P trial )
./v4l2_example -f -o -c 10 > cap_yuv422p.yuv
I've tried to play them with:
ffplay -f rawvideo -pixel_format yuv420p -video_size 1920x1080 -i
cap_yuv420p.yuv
And
ffplay -f rawvideo -pixel_format yuv422p -video_size 1920x1080 -i
cap_yuv422p.yuv
These are the captured video files from my above trials:
https://drive.google.com/folderview?id=0B22GsWueReZTUS1tSHBraTAyZ00&usp=sharing
I probably am doing something wrong. Is there any idea what's wrong in
my configurations or how I can debug it better ?
Best Regards,
Ran
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Using v4l2 API example as-is for video capture
2016-01-08 6:25 Using v4l2 API example as-is for video capture Ran Shalit
@ 2016-01-08 14:03 ` Ran Shalit
2016-01-11 11:29 ` Hans Verkuil
1 sibling, 0 replies; 4+ messages in thread
From: Ran Shalit @ 2016-01-08 14:03 UTC (permalink / raw)
To: linux-media
On Fri, Jan 8, 2016 at 8:25 AM, Ran Shalit <ranshalit@gmail.com> wrote:
> Hello,
>
> I am trying to use v4l2 example from API documentation:
> inhttp://linuxtv.org/downloads/v4l-dvb-apis/capture-example.html .
> As a start, I wanted to first try uding it with vivid (virtual device driver).
> I found excelent vivid documentation in the kernel, which is very helpful:
> https://www.kernel.org/doc/Documentation/video4linux/vivid.txt
>
> But on trying to use the example as-is for capturing video frames into
> file, and playing the file, I encounter difficulties.
> I tried the example as-is, and then tried several resolution,
> pixelformat, different inputs, but it always result with video with a
> sync problems ( the test bars of the video are keep moving in the
> horizontal axis, or the text is changing its location for one frame to
> the next).
>
> I compiled the v4l2 API example AS-IS from:
> http://linuxtv.org/downloads/v4l-dvb-apis/capture-example.html with
> minor modification in the --force part of the example (I also tried
> the example as is without modifications but it did not help), so that
> I choose hd input , and 1920x1080 resolution, V4L2_PIX_FMT_YUV420
> (also tried V4L2_PIX_FMT_YUV422P) , progressive.
>
> if (force_format) {
> input = 3; // <<-- HD input device
> if (-1==xioctl(fd,VIDIOC_S_INPUT,&input))
> {
> errno_exit("VIDIOC_S_INPUT");
> }
> fmt.fmt.pix.width = 1920;
> fmt.fmt.pix.height = 1080;
> fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUV420; // <<-
> tried also V4L2_PIX_FMT_YUV422P
> fmt.fmt.pix.field = V4L2_FIELD_NONE; // <- trying to
> capture progressive
>
> if (-1 == xioctl(fd, VIDIOC_S_FMT, &fmt))
> errno_exit("VIDIOC_S_FMT");
>
> } else {
>
> I run the application with (the compiled code using pixelformat =
> V4L2_PIX_FMT_YUV420 trial ):
>
> ./v4l2_example -f -o -c 10 > cap_yuv420p.yuv
>
> And (the compiled code using pixelformat = V4L2_PIX_FMT_YUV422P trial )
>
> ./v4l2_example -f -o -c 10 > cap_yuv422p.yuv
>
> I've tried to play them with:
>
> ffplay -f rawvideo -pixel_format yuv420p -video_size 1920x1080 -i
> cap_yuv420p.yuv
>
> And
>
> ffplay -f rawvideo -pixel_format yuv422p -video_size 1920x1080 -i
> cap_yuv422p.yuv
>
> These are the captured video files from my above trials:
>
> https://drive.google.com/folderview?id=0B22GsWueReZTUS1tSHBraTAyZ00&usp=sharing
>
> I probably am doing something wrong. Is there any idea what's wrong in
> my configurations or how I can debug it better ?
>
> Best Regards,
> Ran
Hi,
I did manage to play the video with the example as-is (no code modification)
But It seems that the captured video is always the same: 422 YUYV.
I tried to change in code to other formats (in the section below force
option as I wrote in the previous post) ,
but although it gives no error (and VIDIOC_G_FMT returns the new
format) , and yet - the final video is always in 422, YUYV format.
Is there any hint why we can't change the format to YUV420 ?
Regards,
Ran
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Using v4l2 API example as-is for video capture
2016-01-08 6:25 Using v4l2 API example as-is for video capture Ran Shalit
2016-01-08 14:03 ` Ran Shalit
@ 2016-01-11 11:29 ` Hans Verkuil
2016-01-11 11:56 ` Ran Shalit
1 sibling, 1 reply; 4+ messages in thread
From: Hans Verkuil @ 2016-01-11 11:29 UTC (permalink / raw)
To: Ran Shalit, linux-media
On 01/08/2016 07:25 AM, Ran Shalit wrote:
> Hello,
>
> I am trying to use v4l2 example from API documentation:
> inhttp://linuxtv.org/downloads/v4l-dvb-apis/capture-example.html .
> As a start, I wanted to first try uding it with vivid (virtual device driver).
> I found excelent vivid documentation in the kernel, which is very helpful:
> https://www.kernel.org/doc/Documentation/video4linux/vivid.txt
>
> But on trying to use the example as-is for capturing video frames into
> file, and playing the file, I encounter difficulties.
> I tried the example as-is, and then tried several resolution,
> pixelformat, different inputs, but it always result with video with a
> sync problems ( the test bars of the video are keep moving in the
> horizontal axis, or the text is changing its location for one frame to
> the next).
>
> I compiled the v4l2 API example AS-IS from:
> http://linuxtv.org/downloads/v4l-dvb-apis/capture-example.html with
> minor modification in the --force part of the example (I also tried
> the example as is without modifications but it did not help), so that
> I choose hd input , and 1920x1080 resolution, V4L2_PIX_FMT_YUV420
> (also tried V4L2_PIX_FMT_YUV422P) , progressive.
>
> if (force_format) {
> input = 3; // <<-- HD input device
> if (-1==xioctl(fd,VIDIOC_S_INPUT,&input))
> {
> errno_exit("VIDIOC_S_INPUT");
> }
> fmt.fmt.pix.width = 1920;
> fmt.fmt.pix.height = 1080;
> fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUV420; // <<-
> tried also V4L2_PIX_FMT_YUV422P
> fmt.fmt.pix.field = V4L2_FIELD_NONE; // <- trying to
> capture progressive
>
> if (-1 == xioctl(fd, VIDIOC_S_FMT, &fmt))
> errno_exit("VIDIOC_S_FMT");
>
> } else {
>
> I run the application with (the compiled code using pixelformat =
> V4L2_PIX_FMT_YUV420 trial ):
>
> ./v4l2_example -f -o -c 10 > cap_yuv420p.yuv
I'm not sure what you're doing, but this just works for me (I use yuv420p to
play this back).
Note: you can find the same code in v4l-utils in contrib/test. That's the code
I used (with you modifications).
Regards,
Hans
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Using v4l2 API example as-is for video capture
2016-01-11 11:29 ` Hans Verkuil
@ 2016-01-11 11:56 ` Ran Shalit
0 siblings, 0 replies; 4+ messages in thread
From: Ran Shalit @ 2016-01-11 11:56 UTC (permalink / raw)
To: Hans Verkuil; +Cc: linux-media
On Mon, Jan 11, 2016 at 1:29 PM, Hans Verkuil <hverkuil@xs4all.nl> wrote:
> On 01/08/2016 07:25 AM, Ran Shalit wrote:
>> Hello,
>>
>> I am trying to use v4l2 example from API documentation:
>> inhttp://linuxtv.org/downloads/v4l-dvb-apis/capture-example.html .
>> As a start, I wanted to first try uding it with vivid (virtual device driver).
>> I found excelent vivid documentation in the kernel, which is very helpful:
>> https://www.kernel.org/doc/Documentation/video4linux/vivid.txt
>>
>> But on trying to use the example as-is for capturing video frames into
>> file, and playing the file, I encounter difficulties.
>> I tried the example as-is, and then tried several resolution,
>> pixelformat, different inputs, but it always result with video with a
>> sync problems ( the test bars of the video are keep moving in the
>> horizontal axis, or the text is changing its location for one frame to
>> the next).
>>
>> I compiled the v4l2 API example AS-IS from:
>> http://linuxtv.org/downloads/v4l-dvb-apis/capture-example.html with
>> minor modification in the --force part of the example (I also tried
>> the example as is without modifications but it did not help), so that
>> I choose hd input , and 1920x1080 resolution, V4L2_PIX_FMT_YUV420
>> (also tried V4L2_PIX_FMT_YUV422P) , progressive.
>>
>> if (force_format) {
>> input = 3; // <<-- HD input device
>> if (-1==xioctl(fd,VIDIOC_S_INPUT,&input))
>> {
>> errno_exit("VIDIOC_S_INPUT");
>> }
>> fmt.fmt.pix.width = 1920;
>> fmt.fmt.pix.height = 1080;
>> fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUV420; // <<-
>> tried also V4L2_PIX_FMT_YUV422P
>> fmt.fmt.pix.field = V4L2_FIELD_NONE; // <- trying to
>> capture progressive
>>
>> if (-1 == xioctl(fd, VIDIOC_S_FMT, &fmt))
>> errno_exit("VIDIOC_S_FMT");
>>
>> } else {
>>
>> I run the application with (the compiled code using pixelformat =
>> V4L2_PIX_FMT_YUV420 trial ):
>>
>> ./v4l2_example -f -o -c 10 > cap_yuv420p.yuv
>
> I'm not sure what you're doing, but this just works for me (I use yuv420p to
> play this back).
>
> Note: you can find the same code in v4l-utils in contrib/test. That's the code
> I used (with you modifications).
>
> Regards,
>
> Hans
>
Right,
It works for me. I work with Centos 7.2 which comes with kernel
3.10.0. The YUV420 format are missing there, I understood it after
delving into this issue.
Thanks you !
Ran
^ permalink raw reply [flat|nested] 4+ messages in thread
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2016-01-08 14:03 ` Ran Shalit
2016-01-11 11:29 ` Hans Verkuil
2016-01-11 11:56 ` Ran Shalit
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