video: readd codec delay estimation

Approximately reverts commit 3ccac74d. This failed with some avi files,
which do pseudo-VFR by sending packets with empty frames (or repeat
frames, depending on point of view). Specifically, these packets are not
0 bytes, so they don't get skipped by libavformat, as with the usual VFR
avi hack. Instead, the packet contains a VOP with vop_coded=0, so
libavcodec will just return no frame. We could probably distinguish such
skipped frames and delayed frames by explicitly measuring the codec
delay by counting how long it takes to get the very first frame (and
then treat skips as explicit drops), but we may as well simply reinstate
the old code.

To appease to at least one semi-broken case, do not enable this logic on
the RPI, as the FFmpeg MMAL wrapper has arbitrary buffering (and MMAL
itself is asynchronous).

3 files changed, 18 insertions, 0 deletions

diff --git a/video/decode/dec_video.c b/video/decode/dec_video.c
index af55c66811..509daf7cd8 100644
--- a/video/decode/dec_video.c
+++ b/video/decode/dec_video.c
@@ -211,6 +211,10 @@ bool video_init_best_codec(struct dec_video *d_video, char* video_decoders)
 static void add_avi_pts(struct dec_video *d_video, double pts)
 {
     if (pts != MP_NOPTS_VALUE) {
+        int delay = -1;
+        video_vd_control(d_video, VDCTRL_QUERY_UNSEEN_FRAMES, &delay);
+        if (delay >= 0 && delay < d_video->num_buffered_pts)
+            d_video->num_buffered_pts = delay;
         if (d_video->num_buffered_pts == MP_ARRAY_SIZE(d_video->buffered_pts)) {
             MP_ERR(d_video, "Too many buffered pts\n");
         } else {
diff --git a/video/decode/vd.h b/video/decode/vd.h
index 2c812dd4e1..6f5016ac37 100644
--- a/video/decode/vd.h
+++ b/video/decode/vd.h
@@ -42,6 +42,7 @@ extern const vd_functions_t *const mpcodecs_vd_drivers[];
 
 enum vd_ctrl {
     VDCTRL_RESET = 1, // reset decode state after seeking
+    VDCTRL_QUERY_UNSEEN_FRAMES, // current decoder lag
     VDCTRL_FORCE_HWDEC_FALLBACK, // force software decoding fallback
     VDCTRL_GET_HWDEC,
 };
diff --git a/video/decode/vd_lavc.c b/video/decode/vd_lavc.c
index bae0224e02..923fec308b 100644
--- a/video/decode/vd_lavc.c
+++ b/video/decode/vd_lavc.c
@@ -722,6 +722,19 @@ static int control(struct dec_video *vd, int cmd, void *arg)
     case VDCTRL_RESET:
         reset_avctx(vd);
         return CONTROL_TRUE;
+    case VDCTRL_QUERY_UNSEEN_FRAMES: {
+        AVCodecContext *avctx = ctx->avctx;
+        if (!ctx)
+            break;
+        if (ctx->hwdec && ctx->hwdec->type == HWDEC_RPI)
+            break; // MMAL has arbitrary buffering, thus unknown
+        int delay = avctx->has_b_frames;
+        assert(delay >= 0);
+        if (avctx->active_thread_type & FF_THREAD_FRAME)
+            delay += avctx->thread_count - 1;
+        *(int *)arg = delay;
+        return CONTROL_TRUE;
+    }
     case VDCTRL_GET_HWDEC: {
         int hwdec = ctx->hwdec ? ctx->hwdec->type : 0;
         if (!ctx->software_fallback_decoder)