Re: [FFmpeg-devel] [PATCH v2] avcodec/nvenc: add option to skip padding OBUs

[Timo Rothenpieler <timo@rothenpieler.org>]

On 29.03.2025 21:58, Cameron Gutman wrote:
> Some scenarios (such as game streaming or videoconferencing) may use CBR
> to strictly cap the maximum encoded bitrate, but they don't mind the
> bitrate falling below the target if the encoder doesn't need the
> additional headroom.

But why aren't they using vbr with a maxrate then?
I didn't add this conditionally since when in CBR mode, you actually 
really want a constant bitrate.
If you're okay with it dropping lower, why not use another mode with a 
maxrate set?

> Allow users to opt-out of filler data in CBR mode for those usecases
> where it is unwanted.
> 
> Signed-off-by: Cameron Gutman <aicommander@gmail.com>
> ---
> v2: Rebased to resolve conflicts against master
> ---
>   libavcodec/nvenc.c     | 2 +-
>   libavcodec/nvenc.h     | 1 +
>   libavcodec/nvenc_av1.c | 2 ++
>   3 files changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/libavcodec/nvenc.c b/libavcodec/nvenc.c
> index 0f5e772b3e..0f2336b0ec 100644
> --- a/libavcodec/nvenc.c
> +++ b/libavcodec/nvenc.c
> @@ -1624,7 +1624,7 @@ static av_cold int nvenc_setup_av1_config(AVCodecContext *avctx)
>   
>       av1->idrPeriod = cc->gopLength;
>   
> -    if (IS_CBR(cc->rcParams.rateControlMode)) {
> +    if (ctx->filler_data && IS_CBR(cc->rcParams.rateControlMode)) {
>           av1->enableBitstreamPadding = 1;
>       }
>   
> diff --git a/libavcodec/nvenc.h b/libavcodec/nvenc.h
> index e035e123c6..3431457422 100644
> --- a/libavcodec/nvenc.h
> +++ b/libavcodec/nvenc.h
> @@ -309,6 +309,7 @@ typedef struct NvencContext
>       int unidir_b;
>       int split_encode_mode;
>       int mdm, cll;
> +    int filler_data;
>   } NvencContext;
>   
>   int ff_nvenc_encode_init(AVCodecContext *avctx);
> diff --git a/libavcodec/nvenc_av1.c b/libavcodec/nvenc_av1.c
> index 01626113ab..c00817af7b 100644
> --- a/libavcodec/nvenc_av1.c
> +++ b/libavcodec/nvenc_av1.c
> @@ -156,6 +156,8 @@ static const AVOption options[] = {
>                                                               OFFSET(extra_sei),    AV_OPT_TYPE_BOOL,  { .i64 = 1 }, 0, 1, VE },
>       { "a53cc",        "Use A53 Closed Captions (if available)", OFFSET(a53_cc),   AV_OPT_TYPE_BOOL,  { .i64 = 1 }, 0, 1, VE },
>       { "s12m_tc",      "Use timecode (if available)",        OFFSET(s12m_tc),      AV_OPT_TYPE_BOOL,  { .i64 = 1 }, 0, 1, VE },
> +    { "filler_data",  "Use filler data to ensure CBR bitrate is strictly adhered to",
> +                                                            OFFSET(filler_data),  AV_OPT_TYPE_BOOL,  { .i64 = 1 }, 0, 1, VE },
>   #ifdef NVENC_HAVE_H264_AND_AV1_TEMPORAL_FILTER
>       { "tf_level",     "Specifies the strength of the temporal filtering",
>                                                               OFFSET(tf_level),     AV_OPT_TYPE_INT,   { .i64 = -1 }, -1, INT_MAX, VE, .unit = "tf_level" },

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