audio: skip samples and adjust timestamps ourselves

This gets rid of this warning:

  Could not update timestamps for skipped samples.

This required an API addition to FFmpeg (otherwise it would instead
doing arithmetic on the timestamps itself), so whether it works depends
on the FFmpeg version.

audio/decode/ad_lavc.c

@@ -25,6 +25,7 @@
 #include <libavcodec/avcodec.h>
 #include <libavutil/opt.h>
 #include <libavutil/common.h>
+#include <libavutil/intreadwrite.h>
 
 #include "talloc.h"
 
@@ -100,6 +101,22 @@ static void set_data_from_avframe(struct dec_audio *da)
     da->decoded.samples = priv->avframe->nb_samples;
     for (int n = 0; n < da->decoded.num_planes; n++)
         da->decoded.planes[n] = priv->avframe->data[n];
+
+#if HAVE_AVFRAME_SKIP_SAMPLES
+    AVFrameSideData *sd =
+        av_frame_get_side_data(priv->avframe, AV_FRAME_DATA_SKIP_SAMPLES);
+    if (sd && sd->size >= 10) {
+        char *d = sd->data;
+        uint32_t skip = AV_RL32(d + 0);
+        uint32_t pad = AV_RL32(d + 4);
+        if (skip <= da->decoded.samples) {
+            mp_audio_skip_samples(&da->decoded, skip);
+            da->pts_offset += skip;
+        }
+        if (pad <= da->decoded.samples)
+            da->decoded.samples -= pad;
+    }
+#endif
 }
 
 static int init(struct dec_audio *da, const char *decoder)
@@ -139,6 +156,9 @@ static int init(struct dec_audio *da, const char *decoder)
     av_opt_set_double(lavc_context, "drc_scale", opts->ac3drc,
                       AV_OPT_SEARCH_CHILDREN);
 
+    // Let decoder add AV_FRAME_DATA_SKIP_SAMPLES.
+    av_opt_set(lavc_context, "flags2", "+skip_manual", AV_OPT_SEARCH_CHILDREN);
+
     mp_set_avopts(da->log, lavc_context, opts->avopts);
 
     lavc_context->codec_tag = sh->format;
@@ -258,14 +278,14 @@ static int decode_packet(struct dec_audio *da)
     if (!got_frame)
         return mpkt ? AD_OK : AD_EOF;
 
-    set_data_from_avframe(da);
-
     double out_pts = mp_pts_from_av(priv->avframe->pkt_pts, NULL);
     if (out_pts != MP_NOPTS_VALUE) {
         da->pts = out_pts;
         da->pts_offset = 0;
     }
 
+    set_data_from_avframe(da);
+
     MP_DBG(da, "Decoded %d -> %d samples\n", in_len, da->decoded.samples);
     return 0;
 }

old-configure

@@ -828,6 +828,12 @@ api_statement_check \
     libavutil/frame.h \
     'av_frame_get_metadata(NULL)'
 
+api_statement_check \
+    "libavutil AVFrame skip samples metadata" \
+    HAVE_AVFRAME_SKIP_SAMPLES \
+    libavutil/frame.h \
+    'enum AVFrameSideDataType type = AV_FRAME_DATA_SKIP_SAMPLES'
+
 api_statement_check \
     "libavutil QP API" \
     HAVE_AVUTIL_QP_API \

wscript

@@ -422,6 +422,12 @@ Libav libraries ({0}). Aborting.".format(" ".join(libav_pkg_config_checks))
         'func': check_statement('libavutil/frame.h',
                                 'av_frame_get_metadata(NULL)',
                                 use='libav')
+    }, {
+        'name': 'avframe-skip-samples',
+        'desc': 'libavutil AVFrame skip samples metadata',
+        'func': check_statement('libavutil/frame.h',
+                                'enum AVFrameSideDataType type = AV_FRAME_DATA_SKIP_SAMPLES',
+                                use='libav')
     }
 ]