Re: [FFmpeg-devel] [PATCH] avcodec/nvenc: Rework on DTS generation

[Timo Rothenpieler <timo@rothenpieler.org>]

On 17/07/2024 11:47, Zhao Zhili wrote:
> From: Zhao Zhili <zhilizhao@tencent.com>
> 
> Before the patch, the method to generate DTS only works with
> timebase equal to 1/fps. With timebase like 1/1000
> 
> ./ffmpeg -i foo.mp4 -an -c:v h264_nvenc -enc_time_base 1/1000 bar.mp4
> 
> pts 0    dts -3
> pts 160  dts 37
> pts 80   dts 77
> pts 40   dts 117 <-- invalid
> pts 120  dts 157
> pts 320  dts 197
> pts 240  dts 237
> pts 200  dts 277 <-- invalid
> pts 280  dts 317 <-- invalid
> 
> The generated DTS can be larger than PTS, since it only reorder the
> input PTS and minus the number of frame delay, which doesn't take
> timebase into account. It should minus the "time" of frame delay.
> 
> 9a245bd trying to fix the issue, but the implementation is incomplete,
> which only use time_base.num. Then it got reverted by ac7c265b33b.
> 
> After this patch:
> 
> pts 0    dts -120
> pts 160  dts -80
> pts 80   dts -40
> pts 40   dts 0
> pts 120  dts 40
> pts 320  dts 80
> pts 240  dts 120
> pts 200  dts 160
> pts 280  dts 200
> ---
>   libavcodec/nvenc.c | 62 ++++++++++++++++++++++++++++++++++++++--------
>   libavcodec/nvenc.h |  3 +++
>   2 files changed, 55 insertions(+), 10 deletions(-)
> 
> diff --git a/libavcodec/nvenc.c b/libavcodec/nvenc.c
> index ab92395ed6..34448462f0 100644
> --- a/libavcodec/nvenc.c
> +++ b/libavcodec/nvenc.c
> @@ -1893,7 +1893,8 @@ static av_cold int nvenc_setup_surfaces(AVCodecContext *avctx)
>       if (!ctx->frame_data_array)
>           return AVERROR(ENOMEM);
>   
> -    ctx->timestamp_list = av_fifo_alloc2(ctx->nb_surfaces, sizeof(int64_t), 0);
> +    ctx->timestamp_list = av_fifo_alloc2(ctx->nb_surfaces + ctx->encode_config.frameIntervalP,
> +                                         sizeof(int64_t), 0);
>       if (!ctx->timestamp_list)
>           return AVERROR(ENOMEM);
>   
> @@ -2347,26 +2348,65 @@ static inline int64_t timestamp_queue_dequeue(AVFifo *queue)
>       return timestamp;
>   }
>   
> +static inline int64_t timestamp_queue_peek(AVFifo *queue, size_t index)
> +{
> +    int64_t timestamp = AV_NOPTS_VALUE;
> +    av_fifo_peek(queue, &timestamp, 1, index);
> +
> +    return timestamp;
> +}
> +
>   static int nvenc_set_timestamp(AVCodecContext *avctx,
>                                  NV_ENC_LOCK_BITSTREAM *params,
>                                  AVPacket *pkt)
>   {
>       NvencContext *ctx = avctx->priv_data;
> +    int delay;
> +    int64_t delay_time;
>   
>       pkt->pts = params->outputTimeStamp;
>   
> -    if (avctx->codec_descriptor->props & AV_CODEC_PROP_REORDER) {
> -FF_DISABLE_DEPRECATION_WARNINGS
> -        pkt->dts = timestamp_queue_dequeue(ctx->timestamp_list) -
> -#if FF_API_TICKS_PER_FRAME
> -            FFMAX(avctx->ticks_per_frame, 1) *
> -#endif
> -            FFMAX(ctx->encode_config.frameIntervalP - 1, 0);
> -FF_ENABLE_DEPRECATION_WARNINGS
> -    } else {
> +    if (!(avctx->codec_descriptor->props & AV_CODEC_PROP_REORDER)) {
>           pkt->dts = pkt->pts;
> +        return 0;
> +    }
> +
> +    // This can be more than necessary, but we don't know the real reorder delay.
> +    delay = FFMAX(ctx->encode_config.frameIntervalP - 1, 0);
> +    if (ctx->output_frame_num >= delay) {
> +        pkt->dts = timestamp_queue_dequeue(ctx->timestamp_list);
> +        ctx->output_frame_num++;
> +        return 0;
>       }
>   
> +    delay_time = ctx->initial_delay_time;
> +    if (!delay_time) {
> +        int64_t t1, t2, t3;
> +        t1 = timestamp_queue_peek(ctx->timestamp_list, delay);
> +        t2 = timestamp_queue_peek(ctx->timestamp_list, 0);
> +        t3 = (delay > 1) ? timestamp_queue_peek(ctx->timestamp_list, 1) : t1;
> +
> +        if (t1 != AV_NOPTS_VALUE) {
> +            delay_time = t1 - t2;
> +        } else if (avctx->framerate.num > 0 && avctx->framerate.den > 0) {
> +            delay_time = av_rescale_q(delay, (AVRational) {avctx->framerate.den, avctx->framerate.num},
> +                                      avctx->time_base);
> +        } else if (t3 != AV_NOPTS_VALUE) {
> +            delay_time = delay * (t3 - t2);
> +        } else {
> +            delay_time = delay;
> +        }
> +        ctx->initial_delay_time = delay_time;
> +    }
> +
> +    /* The following method is simple, but doesn't guarantee monotonic with VFR
> +     * when delay_time isn't accurate (that is, t1 == AV_NOPTS_VALUE)
> +     *
> +     * dts = timestamp_queue_peek(ctx->timestamp_list, ctx->output_frame_num) - delay_time
> +     */
> +    pkt->dts = timestamp_queue_peek(ctx->timestamp_list, 0) - delay_time * (delay - ctx->output_frame_num) / delay;
> +    ctx->output_frame_num++;
> +
>       return 0;
>   }
>   
> @@ -2902,4 +2942,6 @@ av_cold void ff_nvenc_encode_flush(AVCodecContext *avctx)
>   
>       nvenc_send_frame(avctx, NULL);
>       av_fifo_reset2(ctx->timestamp_list);
> +    ctx->output_frame_num = 0;
> +    ctx->initial_delay_time = 0;
>   }
> diff --git a/libavcodec/nvenc.h b/libavcodec/nvenc.h
> index 09de00badc..dc7fe41951 100644
> --- a/libavcodec/nvenc.h
> +++ b/libavcodec/nvenc.h
> @@ -206,6 +206,9 @@ typedef struct NvencContext
>       AVFifo *output_surface_queue;
>       AVFifo *output_surface_ready_queue;
>       AVFifo *timestamp_list;
> +    // This is for DTS calculating, reset after flush
> +    int64_t output_frame_num;
> +    int64_t initial_delay_time;
>   
>       NV_ENC_SEI_PAYLOAD *sei_data;
>       int sei_data_size;

This looks good on first glance, but I'm away from any nvenc capable PC 
for the next two weeks, so it'll unfortunately be a while until I can 
properly test and apply.


Timo
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