Re: [FFmpeg-devel] [PATCH v2] avcodec/nvenc: High bit depth encoding for HEVC

[Timo Rothenpieler <timo@rothenpieler.org>]

On 19/04/2024 13:29, Lynne wrote:
> Apr 19, 2024, 10:39 by ffmpeg-devel@ffmpeg.org:
> 
>> From: Diego Felix de Souza <ddesouza@nvidia.com>
>>
>> Adding 10-bit encoding support for HEVC if the input is 8-bit. In
>> case of 8-bit input content, NVENC performs an internal CUDA 8 to
>> 10-bit conversion of the input prior to encoding. Currently, only
>> AV1 supports encoding 8-bit content as 10-bit.
>>
>> Signed-off-by: Diego Felix de Souza <ddesouza@nvidia.com>
>> ---
>>   libavcodec/nvenc.c      | 10 +++++-----
>>   libavcodec/nvenc_hevc.c |  3 +++
>>   2 files changed, 8 insertions(+), 5 deletions(-)
>>
>> diff --git a/libavcodec/nvenc.c b/libavcodec/nvenc.c
>> index 794174a53f..e48224347d 100644
>> --- a/libavcodec/nvenc.c
>> +++ b/libavcodec/nvenc.c
>> @@ -514,7 +514,7 @@ static int nvenc_check_capabilities(AVCodecContext *avctx)
>>   }
>>
>>   ret = nvenc_check_cap(avctx, NV_ENC_CAPS_SUPPORT_10BIT_ENCODE);
>> -    if (IS_10BIT(ctx->data_pix_fmt) && ret <= 0) {
>> +    if ((IS_10BIT(ctx->data_pix_fmt) || ctx->highbitdepth) && ret <= 0) {
>>   av_log(avctx, AV_LOG_WARNING, "10 bit encode not supported\n");
>>   return AVERROR(ENOSYS);
>>   }
>> @@ -1420,8 +1420,8 @@ static av_cold int nvenc_setup_hevc_config(AVCodecContext *avctx)
>>   break;
>>   }
>>
>> -    // force setting profile as main10 if input is 10 bit
>> -    if (IS_10BIT(ctx->data_pix_fmt)) {
>> +    // force setting profile as main10 if input is 10 bit or if it should be encoded as 10 bit
>> +    if (IS_10BIT(ctx->data_pix_fmt) || ctx->highbitdepth) {
>>   cc->profileGUID = NV_ENC_HEVC_PROFILE_MAIN10_GUID;
>>   avctx->profile = AV_PROFILE_HEVC_MAIN_10;
>>   }
>> @@ -1435,8 +1435,8 @@ static av_cold int nvenc_setup_hevc_config(AVCodecContext *avctx)
>>   hevc->chromaFormatIDC = IS_YUV444(ctx->data_pix_fmt) ? 3 : 1;
>>
>>   #ifdef NVENC_HAVE_NEW_BIT_DEPTH_API
>> -    hevc->inputBitDepth = hevc->outputBitDepth =
>> -        IS_10BIT(ctx->data_pix_fmt) ? NV_ENC_BIT_DEPTH_10 : NV_ENC_BIT_DEPTH_8;
>> +    hevc->inputBitDepth = IS_10BIT(ctx->data_pix_fmt) ? NV_ENC_BIT_DEPTH_10 : NV_ENC_BIT_DEPTH_8;
>> +    hevc->outputBitDepth = (IS_10BIT(ctx->data_pix_fmt) || ctx->highbitdepth) ? NV_ENC_BIT_DEPTH_10 : NV_ENC_BIT_DEPTH_8;
>>   #else
>>   hevc->pixelBitDepthMinus8 = IS_10BIT(ctx->data_pix_fmt) ? 2 : 0;
>>   #endif
>> diff --git a/libavcodec/nvenc_hevc.c b/libavcodec/nvenc_hevc.c
>> index b949cb1bd7..d54e5f2512 100644
>> --- a/libavcodec/nvenc_hevc.c
>> +++ b/libavcodec/nvenc_hevc.c
>> @@ -183,6 +183,9 @@ static const AVOption options[] = {
>>   { "fullres",      "Two Pass encoding is enabled where first Pass is full resolution",
>>   0,                    AV_OPT_TYPE_CONST, { .i64 = NV_ENC_TWO_PASS_FULL_RESOLUTION },    0,                          0,                               VE, .unit = "multipass" },
>>   #endif
>> +#ifdef NVENC_HAVE_NEW_BIT_DEPTH_API
>> +    { "highbitdepth", "Enable 10 bit encode for 8 bit input",OFFSET(highbitdepth),AV_OPT_TYPE_BOOL,  { .i64 = 0 }, 0, 1, VE },
>> +#endif
>>   #ifdef NVENC_HAVE_LDKFS
>>   { "ldkfs",        "Low delay key frame scale; Specifies the Scene Change frame size increase allowed in case of single frame VBV and CBR",
>>   OFFSET(ldkfs),        AV_OPT_TYPE_INT,   { .i64 = 0 }, 0, UCHAR_MAX, VE },
>> --
>> 2.34.1
>>
> 
> Rather than introducing a new setting, could you
> instead use AVCodecContext.sw_pix_fmt?
> It's currently documented as being unused for encoding,
> but it fits the purpose.
> Vulkan can also use it.

I'm not sure I'm a fan of that.
Setting sw_pix_fmt to some arbitrary 10bit format seems super random.
How would that even look like from a users point of view who wanted to 
utilize this up-conversion mode via cli?
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