Re: [FFmpeg-devel] [PATCH v2 1/8] avutil/hwcontext: Add hwdevice type for V4L2 Request API

[Jonas Karlman <jonas@kwiboo.se>]

Hi Lynne,

On 2024-08-06 14:46, Lynne via ffmpeg-devel wrote:
> On 06/08/2024 11:06, Jonas Karlman wrote:
>> Add a hwdevice type for V4L2 Request API with transfer_data_from support
>> for AV_PIX_FMT_DRM_PRIME, based on AV_HWDEVICE_TYPE_DRM.
>>
>> AVV4L2RequestDeviceContext.media_fd can be set by the application or a
>> media device path can be supplied when hwdevice is created. When none
>> is supplied it default to -1 and hwaccel will auto-detect a media device
>> with a capable video device.
>>
>> Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
>> ---
>>   configure                         |   7 +
>>   libavutil/Makefile                |   3 +
>>   libavutil/hwcontext.c             |   4 +
>>   libavutil/hwcontext.h             |   1 +
>>   libavutil/hwcontext_internal.h    |   1 +
>>   libavutil/hwcontext_v4l2request.c | 261 ++++++++++++++++++++++++++++++
>>   libavutil/hwcontext_v4l2request.h |  41 +++++
>>   7 files changed, 318 insertions(+)
>>   create mode 100644 libavutil/hwcontext_v4l2request.c
>>   create mode 100644 libavutil/hwcontext_v4l2request.h
>>

[snip]

>> diff --git a/libavutil/hwcontext_v4l2request.h b/libavutil/hwcontext_v4l2request.h
>> new file mode 100644
>> index 0000000000..0fe42f97b4
>> --- /dev/null
>> +++ b/libavutil/hwcontext_v4l2request.h
>> @@ -0,0 +1,41 @@
>> +/*
>> + * This file is part of FFmpeg.
>> + *
>> + * FFmpeg is free software; you can redistribute it and/or
>> + * modify it under the terms of the GNU Lesser General Public
>> + * License as published by the Free Software Foundation; either
>> + * version 2.1 of the License, or (at your option) any later version.
>> + *
>> + * FFmpeg is distributed in the hope that it will be useful,
>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> + * Lesser General Public License for more details.
>> + *
>> + * You should have received a copy of the GNU Lesser General Public
>> + * License along with FFmpeg; if not, write to the Free Software
>> + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
>> + */
>> +
>> +#ifndef AVUTIL_HWCONTEXT_V4L2REQUEST_H
>> +#define AVUTIL_HWCONTEXT_V4L2REQUEST_H
>> +
>> +/**
>> + * @file
>> + * An API-specific header for AV_HWDEVICE_TYPE_V4L2REQUEST.
>> + */
>> +
>> +/**
>> + * V4L2 Request API device details.
>> + *
>> + * Allocated as AVHWDeviceContext.hwctx
>> + */
>> +typedef struct AVV4L2RequestDeviceContext {
>> +    /**
>> +     * File descriptor of media device.
>> +     *
>> +     * Defaults to -1 for auto-detect.
>> +     */
>> +    int media_fd;
>> +} AVV4L2RequestDeviceContext;
>> +
>> +#endif /* AVUTIL_HWCONTEXT_V4L2REQUEST_H */
> 
> Any reason you're not using hwcontext_drm.h?
> 

The DRM hwdevice/hwcontext requires a DRM/DRI device, however V4L2
decoding does not require a DRM/DRI device at all to do decode.

This became fully apparent on a Rockchip RK3588 device that at the time
did not have gpu or display support in mainline, yet it had a working
AV1 decoder. Using a DRM hwdevice/hwcontext required an application to
supply a path to a none existing DRI device.

Instead a separate new hwdevice type is introduced, for now it can be
used to define a specific media device to use /dev/mediaX, in future it
could be extended to support options to specify what /dev/videoX device
to use for decoding.

These hwaccels only want to produce AV_PIX_FMT_DRM_PRIME output buffers
and does not want to be tied to any DRM/DRI device, if there is better
ways to do this, please advise.

Regards,
Jonas

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