On 11/07/2017 11:35 PM, Carlos Rafael Giani wrote:
> I was discussing this with Tim earlier, and there was a little
> confusion. He meant V4L2_FIELD_SEQ_TB/BT, not V4L2_FIELD_INTERLACED.
>
> When I tried out 1080i50 with HDMI in and the i.MX6, I got something
> that looks like V4L2_FIELD_SEQ_TB. The question though is: are the field
> rows always arranged like this with interlaced HDMI? Or does this depend
> on the source? Could it for example be possible that 2 HDMI cameras
> deliver both interlaced video, but the first one delivers
> V4L2_FIELD_INTERLACED, and the second delivers V4L2_FIELD_SEQ_TB? Could
> this happen?
HDMI doesn't deliver any of the V4L2_FIELD_* formats, those are a property
of the DMA engine and/or possible processing blocks earlier in the video
pipeline.
Interlaced formats as transmitted over HDMI are sent as a sequence of fields.
All defined interlaced formats except for one send the top field first, then
the bottom field. The exception (I'm 99% certain of that) is 720x480i (aka NTSC)
which sends the bottom field before the top field.
The video pipeline will typically DMA each field in a separate buffer (i.e.
FIELD_ALTERNATE) or concatenate two fields in one buffer (SEQ_TB or SEQ_BT for
720x480i), although the latter is less common. There is little point to it
since it would just increase the latency with little benefit.
If the video pipeline contains a deinterlacer, then FIELD_NONE is also an
option.
Regards,
Hans
>
>
> On 2017-11-07 19:40, Tim Harvey wrote:
>> Greetings,
>>
>> I'm trying to understand the various field orders supported by v4l2
>> [1]. Do HDMI sources always use V4L2_FIELD_INTERLACED or can they
>> support alternate modes as well?
>>
>> Regards,
>>
>> Tim
>>
>> [1] -
>> https://www.linuxtv.org/downloads/legacy/video4linux/API/V4L2_API/spec/ch03s06.html
>
