ffserver: fix seeking with ?date=...

Regression since 5f847bf61d.

After this commit, timestamps pushed by FFmpeg won't be relative
anymore, but absolute (based on the date/time at the beginning of the
push). This will allow seeking to work properly. Before this patch, the
seek was done, but ffm timestamps were way smallers than the absolute
requested timestamp (based on a date), so the seek was done, but to the
end of the stream (which was similar to no effect at all).

ffmpeg_opt.c

@@ -1368,8 +1368,11 @@ static int read_ffserver_streams(OptionsContext *o, AVFormatContext *s, const ch
             choose_pixel_fmt(st, codec, st->codec->pix_fmt);
     }
 
+    /* ffserver seeking with date=... needs a date reference */
+    err = parse_option(o, "metadata", "creation_time=now", options);
+
     avformat_close_input(&ic);
-    return 0;
+    return err;
 }
 
 static void init_output_filter(OutputFilter *ofilter, OptionsContext *o,

libavformat/ffm.h

@@ -54,6 +54,7 @@ typedef struct FFMContext {
     int64_t dts;
     uint8_t *packet_ptr, *packet_end;
     uint8_t packet[FFM_PACKET_SIZE];
+    int64_t start_time;
 } FFMContext;
 
 int64_t ffm_read_write_index(int fd);

libavformat/ffmenc.c

@@ -22,6 +22,7 @@
 #include "libavutil/intreadwrite.h"
 #include "libavutil/intfloat.h"
 #include "libavutil/avassert.h"
+#include "libavutil/parseutils.h"
 #include "avformat.h"
 #include "internal.h"
 #include "ffm.h"
@@ -85,11 +86,18 @@ static void ffm_write_data(AVFormatContext *s,
 static int ffm_write_header(AVFormatContext *s)
 {
     FFMContext *ffm = s->priv_data;
+    AVDictionaryEntry *t;
     AVStream *st;
     AVIOContext *pb = s->pb;
     AVCodecContext *codec;
     int bit_rate, i;
 
+    if (t = av_dict_get(s->metadata, "creation_time", NULL, 0)) {
+        int ret = av_parse_time(&ffm->start_time, t->value, 0);
+        if (ret < 0)
+            return ret;
+    }
+
     ffm->packet_size = FFM_PACKET_SIZE;
 
     /* header */
@@ -198,11 +206,12 @@ static int ffm_write_header(AVFormatContext *s)
 
 static int ffm_write_packet(AVFormatContext *s, AVPacket *pkt)
 {
+    FFMContext *ffm = s->priv_data;
     int64_t dts;
     uint8_t header[FRAME_HEADER_SIZE+4];
     int header_size = FRAME_HEADER_SIZE;
 
-    dts = pkt->dts;
+    dts = ffm->start_time + pkt->dts;
     /* packet size & key_frame */
     header[0] = pkt->stream_index;
     header[1] = 0;
@@ -210,7 +219,7 @@ static int ffm_write_packet(AVFormatContext *s, AVPacket *pkt)
         header[1] |= FLAG_KEY_FRAME;
     AV_WB24(header+2, pkt->size);
     AV_WB24(header+5, pkt->duration);
-    AV_WB64(header+8, pkt->pts);
+    AV_WB64(header+8, ffm->start_time + pkt->pts);
     if (pkt->pts != pkt->dts) {
         header[1] |= FLAG_DTS;
         AV_WB32(header+16, pkt->pts - pkt->dts);