use correct field number for video according to specs, patch by Thierry Foucu,...

use correct field number for video according to specs, patch by Thierry Foucu, tfoucu at gmail dot com

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@17214 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavformat/gxfenc.c

@@ -728,11 +728,19 @@ static int gxf_parse_mpeg_frame(GXFStreamContext *sc, const uint8_t *buf, int si
 static int gxf_write_media_preamble(ByteIOContext *pb, GXFContext *ctx, AVPacket *pkt, int size)
 {
     GXFStreamContext *sc = ctx->fc->streams[pkt->stream_index]->priv_data;
-    int64_t dts = av_rescale_rnd(pkt->dts, ctx->sample_rate, sc->codec->time_base.den, AV_ROUND_UP);
+    unsigned field_nb;
+    /* If the video is frame-encoded, the frame numbers shall be represented by
+     * even field numbers.
+     * see SMPTE360M-2004  6.4.2.1.3 Media field number */
+    if (sc->codec->codec_type == CODEC_TYPE_VIDEO) {
+        field_nb = ctx->nb_fields;
+    } else {
+        field_nb = av_rescale_rnd(pkt->dts, ctx->sample_rate, sc->codec->time_base.den, AV_ROUND_UP);
+    }
 
     put_byte(pb, sc->media_type);
     put_byte(pb, sc->index);
-    put_be32(pb, dts);
+    put_be32(pb, field_nb);
     if (sc->codec->codec_type == CODEC_TYPE_AUDIO) {
         put_be16(pb, 0);
         put_be16(pb, size / 2);
@@ -754,7 +762,7 @@ static int gxf_write_media_preamble(ByteIOContext *pb, GXFContext *ctx, AVPacket
         put_be24(pb, 0);
     } else
         put_be32(pb, size);
-    put_be32(pb, dts);
+    put_be32(pb, field_nb);
     put_byte(pb, 1); /* flags */
     put_byte(pb, 0); /* reserved */
     return 16;