> On Dec 17, 2024, at 06:48, Scott Theisen <scott.the....@gmail.com> wrote:
>
> On 12/15/24 22:15, Zhao Zhili wrote:
>>
>>> On Dec 15, 2024, at 12:14, Scott Theisen<scott.the....@gmail.com> wrote:
>>>
>>> Based on patches by Lukas Rusak from
>>> https://github.com/lrusak/FFmpeg/commits/v4l2-drmprime-v4
>>>
>>> libavcodec: v4l2m2m: output AVDRMFrameDescriptor
>>> https://github.com/lrusak/FFmpeg/commit/2cb8052ac65a56d8a3f347a1e6f12d4449a5a614
>>>
>>> libavcodec: v4l2m2m: depends on libdrm
>>> https://github.com/lrusak/FFmpeg/commit/ab4cf3e6fb37cffdebccca52e36a7b2deb7e729f
>>>
>>> libavcodec: v4l2m2m: set format_modifier to DRM_FORMAT_MOD_LINEAR
>>> https://github.com/lrusak/FFmpeg/commit/9438a6efa29c7c7ec80c39c9b013b9a12d7b5f33
>>>
>>> libavcodec: v4l2m2m: only mmap the buffer when it is output type and drm
>>> prime is used
>>> https://github.com/lrusak/FFmpeg/commit/093656607863e47630de2d1cfcf0ac8e4b93a69e
>>>
>>> libavcodec: v4l2m2m: allow using software pixel formats
>>> https://github.com/lrusak/FFmpeg/commit/8405b573e83838e6b2fea99825fbef32ee9f7767
>>>
>>> libavcodec: v4l2m2m: implement hwcontext
>>> https://github.com/lrusak/FFmpeg/commit/b2c1f1eb39b54bf034497a7f2a7f23855d0a7cde
>>>
>>> libavcodec: v4l2m2m: implement flush
>>> https://github.com/lrusak/FFmpeg/commit/e793ef82727d6d6f55c40844463d476e7e84efad
>>>
>>> Originally added to MythTV in:
>>> FFmpeg: Patch FFmpeg for V4L2 codecs DRM PRIME support
>>> https://github.com/MythTV/mythtv/commit/cc7572f9b26189ad5d5d504c05f08e53e4e61b54
>>>
>>> FFmpeg: Re-apply v4l2 memory to memory DRM_PRIME support
>>> https://github.com/MythTV/mythtv/commit/1c942720591b5b7820abe9ed0d805afabbdffe3c
>>>
>>> modified in:
>>> V4L2 Codecs: Fix lockup when seeking
>>> https://github.com/MythTV/mythtv/commit/fdc0645aba9a9ad373888bd62ebcbc83a3feb7e5
>>>
>>> v4l2_buffers: Add some libdrm ifdef's
>>> https://github.com/MythTV/mythtv/commit/336df1067abfa4fe7cf611541e5b6f3561fc81a2
>>>
>>> !!!!
>>> NB: libavcodec/v4l2_m2m_dec.c: v4l2_decode_init(): I'm returning -1
>>> since I don't know what error code I should use.
>>>
>>> Note also Lucas Rusak's v5 series:
>>> closer diff to current state, otherwise unchanged
>>> libavcodec: v4l2m2m: output AVDRMFrameDescriptor
>>> https://github.com/lrusak/FFmpeg/commit/c6b85ed30f06ea99513b13cc768a922ebe4d68c2
>>>
>>> new option:
>>> libavcodec: v4l2m2m: add option to specify pixel format used by the decoder
>>> https://github.com/lrusak/FFmpeg/commit/ffc4419f456c00ab71cf93f792b0473c6de14e64
>>>
>>> additional code vs v4
>>> libavcodec: v4l2m2m: implement flush
>>> https://github.com/lrusak/FFmpeg/commit/8595d06d4909bbec0aa14625fcfc869c6bcef696
>>> ---
>>> configure | 1 +
>>> libavcodec/v4l2_buffers.c | 206 +++++++++++++++++++++++++++++++++++---
>>> libavcodec/v4l2_buffers.h | 4 +
>>> libavcodec/v4l2_context.c | 43 +++++++-
>>> libavcodec/v4l2_context.h | 2 +
>>> libavcodec/v4l2_m2m.h | 5 +
>>> libavcodec/v4l2_m2m_dec.c | 62 ++++++++++++
>>> 7 files changed, 305 insertions(+), 18 deletions(-)
>>>
>>> diff --git a/configure b/configure
>>> index bf55ba67fa..5f02cf3b51 100755
>>> --- a/configure
>>> +++ b/configure
>>> @@ -3770,6 +3770,7 @@ sndio_indev_deps="sndio"
>>> sndio_outdev_deps="sndio"
>>> v4l2_indev_deps_any="linux_videodev2_h sys_videoio_h"
>>> v4l2_indev_suggest="libv4l2"
>>> +v4l2_outdev_deps="libdrm"
>> Why v4l2_outdev when the patch is for libavcodec?
>
> Lukas Rusak appears to have only submitted up to v3 of his patches in 2018.
>
> This appears to be from a comment in
> https://patchwork.ffmpeg.org/project/ffmpeg/patch/4bbeff66-6123-9296-5775-96d75809e...@jkqxz.net/
>
> However, with the `#if CONFIG_LIBDRM`s added by Mark Kendall for MythTV, I
> don't think it is a hard dependency.
>
> ...
>>> diff --git a/libavcodec/v4l2_m2m_dec.c b/libavcodec/v4l2_m2m_dec.c
>>> index aa2d759e1e..cfeee7f2fb 100644
>>> --- a/libavcodec/v4l2_m2m_dec.c
>>> +++ b/libavcodec/v4l2_m2m_dec.c
>>> @@ -23,12 +23,17 @@
>>>
>>> #include <linux/videodev2.h>
>>> #include <sys/ioctl.h>
>>> +
>>> +#include "libavutil/hwcontext.h"
>>> +#include "libavutil/hwcontext_drm.h"
>>> #include "libavutil/pixfmt.h"
>>> #include "libavutil/pixdesc.h"
>>> #include "libavutil/opt.h"
>>> #include "libavcodec/avcodec.h"
>>> #include "codec_internal.h"
>>> #include "libavcodec/decode.h"
>>> +#include "libavcodec/internal.h"
>>> +#include "libavcodec/hwconfig.h"
>>>
>>> #include "v4l2_context.h"
>>> #include "v4l2_m2m.h"
>>> @@ -205,7 +210,44 @@ static av_cold int v4l2_decode_init(AVCodecContext
>>> *avctx)
>>> capture->av_codec_id = AV_CODEC_ID_RAWVIDEO;
>>> capture->av_pix_fmt = avctx->pix_fmt;
>>>
>>> + /* the client requests the codec to generate DRM frames:
>>> + * - data[0] will therefore point to the returned
>>> AVDRMFrameDescriptor
>>> + * check the ff_v4l2_buffer_to_avframe conversion function.
>>> + * - the DRM frame format is passed in the DRM frame descriptor
>>> layer.
>>> + * check the v4l2_get_drm_frame function.
>>> + */
>>> + {
>>> + const enum AVPixelFormat *pix_fmts = NULL;
>>> + int num_pix_fmts = 0;
>>> + ret = avcodec_get_supported_config(avctx, NULL,
>>> AV_CODEC_CONFIG_PIX_FORMAT,
>>> + 0, (const void **) &pix_fmts,
>>> &num_pix_fmts);
>> I don’t think here is the meant use case for avcodec_get_supported_config.
>> Specify available pixel format directly in pix_fmts.
>>
>>> + if (ret < 0)
>>> + return ret;
>>> + if (pix_fmts == NULL || num_pix_fmts < 1)
>>> + return -1;
>> There is no which error code to use issue after remove
>> avcodec_get_supported_config.
>>
>
> AVCodec::pix_fmts was deprecated, so I replaced it with
> avcodec_get_supported_config() in
> https://github.com/ulmus-scott/FFmpeg/commit/7ac4b4fc2282b4fdda78ffb1a446ceb85b681661
>
> Was that incorrect?
Firstly, AVCodec::pix_fmts was deprecated, which should be replaced by
FFCodec::get_supported_config
callback for **internal implementation**. avcodec_get_supported_config is
towards for libavcodec API users.
Secondly, AVCodec::pix_fmts and FFCodec::get_supported_config is for
**encoder**. For decoder, it’s
AVCodecContext::get_format callback to do the negotiate, for example,
h264_slice.c get_pixel_format().
>
>>> + switch (ff_get_format(avctx, pix_fmts)) {
>>> + case AV_PIX_FMT_DRM_PRIME:
>>> + s->output_drm = 1;
>>> + break;
>>> + case AV_PIX_FMT_NONE:
>>> + return 0;
>>> + break;
>> Why return 0 for AV_PIX_FMT_NONE? It’s suspicious.
>> ‘break’ can be removed.
>
> That is from
> https://github.com/lrusak/FFmpeg/commit/8405b573e83838e6b2fea99825fbef32ee9f7767
>
> I agree return 0 is strange. All I can say is that is what the code used by
> MythTV is and has been for years. (Maybe MythTV always requests
> AV_PIX_FMT_DRM_PRIME?)
>
> This change is not used by MythTV but maybe
> https://github.com/lrusak/FFmpeg/commit/ffc4419f456c00ab71cf93f792b0473c6de14e64
> is related or an alternate way of requesting the pixel format?
>
>>> + default:
>>> + break;
>>> + }
>>> + }
>>> +
>>> + s->device_ref = av_hwdevice_ctx_alloc(AV_HWDEVICE_TYPE_DRM);
>>> + if (!s->device_ref) {
>>> + ret = AVERROR(ENOMEM);
>>> + return ret;
>>> + }
>> I’m not sure whether there is use case to let user specify device?
>
> This is from
> https://github.com/lrusak/FFmpeg/commit/b2c1f1eb39b54bf034497a7f2a7f23855d0a7cde
>
> I don't know what you mean by "let user specify device".
User can create a DRM hw device directly via hwcontext API, and provided to
decoder via
AVCodecContext::hw_device_ctx. It don’t looks right to always create hw device
directly inside
the decoder implementation.
>
>>
>>> +
>>> s->avctx = avctx;
>>> + ret = av_hwdevice_ctx_init(s->device_ref);
>>> + if (ret < 0)
>>> + return ret;
>>> +
>>> ret = ff_v4l2_m2m_codec_init(priv);
>>> if (ret) {
>>> av_log(avctx, AV_LOG_ERROR, "can't configure decoder\n");
>>> @@ -220,6 +262,16 @@ static av_cold int v4l2_decode_close(AVCodecContext
>>> *avctx)
>>> return ff_v4l2_m2m_codec_end(avctx->priv_data);
>>> }
>>>
>>> +static void v4l2_flush(AVCodecContext *avctx)
>>> +{
>>> + V4L2m2mPriv *priv = avctx->priv_data;
>>> + V4L2m2mContext* s = priv->context;
>>> +
>>> + /* wait for pending buffer references */
>>> + if (atomic_load(&s->refcount))
>>> + while(sem_wait(&s->refsync) == -1 && errno == EINTR);
>>> +}
>> Does refcount depends on users behavior like holding a frame? Is it possible
>> to run into deadlock here, e.g.,
>> user request flush while holding some frames?
>
> I don't know, but Lukas Rusak removed that in his v5 patch (not used by
> MythTV)
> https://github.com/lrusak/FFmpeg/commit/8595d06d4909bbec0aa14625fcfc869c6bcef696
>
> Original v4 patch for reference:
> https://github.com/lrusak/FFmpeg/commit/e793ef82727d6d6f55c40844463d476e7e84efad
>
>>> +
>>> #define OFFSET(x) offsetof(V4L2m2mPriv, x)
>>> #define FLAGS AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_DECODING_PARAM
>>>
>>> @@ -230,6 +282,11 @@ static const AVOption options[] = {
>>> { NULL},
>>> };
>>>
>>> +static const AVCodecHWConfigInternal *v4l2_m2m_hw_configs[] = {
>>> + HW_CONFIG_INTERNAL(DRM_PRIME),
>> Depends on whether allow user to specify drm device.
>
> This is from the main patch
> https://github.com/lrusak/FFmpeg/commit/2cb8052ac65a56d8a3f347a1e6f12d4449a5a614
>
> Unless this is used internally by FFmpeg, MythTV does not appear to use it.
>
> Regards,
>
> Scott Theisen
> _______________________________________________
> ffmpeg-devel mailing list
> ffmpeg-devel@ffmpeg.org
> https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>
> To unsubscribe, visit link above, or email
> ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
_______________________________________________
ffmpeg-devel mailing list
ffmpeg-devel@ffmpeg.org
https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
To unsubscribe, visit link above, or email
ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
