avcodec/nvenc: refactor dts calculation logic

The old approach used some highly complex delta computation math and
output-delaying.
I do not remember what the initial reasoning behind that was, but given
that we can just offset the dts by the amount of bframes, it seems wholy
unnecessary.

This leaves open an issue with VFR content, for which some more complex
logic might be needed.
Signed-off-by: Timo Rothenpieler <timo@rothenpieler.org>

libavcodec/nvenc.c

@@ -1245,9 +1245,6 @@ static av_cold int nvenc_setup_encoder(AVCodecContext *avctx)
         ctx->encode_config.gopLength = 1;
     }
 
-    ctx->initial_pts[0] = AV_NOPTS_VALUE;
-    ctx->initial_pts[1] = AV_NOPTS_VALUE;
-
     nvenc_recalc_surfaces(avctx);
 
     nvenc_setup_rate_control(avctx);
@@ -1819,30 +1816,9 @@ static int nvenc_set_timestamp(AVCodecContext *avctx,
     NvencContext *ctx = avctx->priv_data;
 
     pkt->pts = params->outputTimeStamp;
+    pkt->dts = timestamp_queue_dequeue(ctx->timestamp_list);
 
-    /* generate the first dts by linearly extrapolating the
-     * first two pts values to the past */
-    if (avctx->max_b_frames > 0 && !ctx->first_packet_output &&
-        ctx->initial_pts[1] != AV_NOPTS_VALUE) {
-        int64_t ts0 = ctx->initial_pts[0], ts1 = ctx->initial_pts[1];
-        int64_t delta;
-
-        if ((ts0 < 0 && ts1 > INT64_MAX + ts0) ||
-            (ts0 > 0 && ts1 < INT64_MIN + ts0))
-            return AVERROR(ERANGE);
-        delta = ts1 - ts0;
-
-        if ((delta < 0 && ts0 > INT64_MAX + delta) ||
-            (delta > 0 && ts0 < INT64_MIN + delta))
-            return AVERROR(ERANGE);
-        pkt->dts = ts0 - delta;
-
-        ctx->first_packet_output = 1;
-    } else {
-        pkt->dts = timestamp_queue_dequeue(ctx->timestamp_list);
-    }
-
-    pkt->dts -= avctx->max_b_frames;
+    pkt->dts -= FFMAX(avctx->max_b_frames, 0) * FFMIN(avctx->ticks_per_frame, 1);
 
     return 0;
 }
@@ -1981,12 +1957,6 @@ static int output_ready(AVCodecContext *avctx, int flush)
     NvencContext *ctx = avctx->priv_data;
     int nb_ready, nb_pending;
 
-    /* when B-frames are enabled, we wait for two initial timestamps to
-     * calculate the first dts */
-    if (!flush && avctx->max_b_frames > 0 &&
-        (ctx->initial_pts[0] == AV_NOPTS_VALUE || ctx->initial_pts[1] == AV_NOPTS_VALUE))
-        return 0;
-
     nb_ready   = av_fifo_size(ctx->output_surface_ready_queue)   / sizeof(NvencSurface*);
     nb_pending = av_fifo_size(ctx->output_surface_queue)         / sizeof(NvencSurface*);
     if (flush)
@@ -2109,9 +2079,6 @@ int ff_nvenc_send_frame(AVCodecContext *avctx, const AVFrame *frame)
             return AVERROR_EOF;
 
         ctx->encoder_flushing = 0;
-        ctx->first_packet_output = 0;
-        ctx->initial_pts[0] = AV_NOPTS_VALUE;
-        ctx->initial_pts[1] = AV_NOPTS_VALUE;
         av_fifo_reset(ctx->timestamp_list);
     }
 
@@ -2196,11 +2163,6 @@ int ff_nvenc_send_frame(AVCodecContext *avctx, const AVFrame *frame)
     if (frame) {
         av_fifo_generic_write(ctx->output_surface_queue, &in_surf, sizeof(in_surf), NULL);
         timestamp_queue_enqueue(ctx->timestamp_list, frame->pts);
-
-        if (ctx->initial_pts[0] == AV_NOPTS_VALUE)
-            ctx->initial_pts[0] = frame->pts;
-        else if (ctx->initial_pts[1] == AV_NOPTS_VALUE)
-            ctx->initial_pts[1] = frame->pts;
     }
 
     /* all the pending buffers are now ready for output */

libavcodec/nvenc.h

@@ -161,11 +161,6 @@ typedef struct NvencContext
      * AVCodecContext.pix_fmt when using hwaccel frames on input */
     enum AVPixelFormat data_pix_fmt;
 
-    /* timestamps of the first two frames, for computing the first dts
-     * when B-frames are present */
-    int64_t initial_pts[2];
-    int first_packet_output;
-
     int support_dyn_bitrate;
 
     void *nvencoder;