lavf: use AV_CODEC_PROP_FIELDS where appropriate

H.264 and mpeg12 parsers need to be adjusted at the same time to stop
using the value of AVCodecContext.ticks_per_frame, because it is not set
correctly unless the codec has been opened. Previously this would result
in both the parser and lavf seeing the same incorrect value, which would
cancel out.
Updating lavf and not the parsers would result in correct value in lavf,
but the wrong one in parsers, which would break some tests.

3 files changed, 29 insertions, 18 deletions

diff --git a/libavformat/avformat.c b/libavformat/avformat.c
index 708d90b38c..fea905693d 100644
--- a/libavformat/avformat.c
+++ b/libavformat/avformat.c
@@ -679,6 +679,7 @@ AVRational av_guess_sample_aspect_ratio(AVFormatContext *format, AVStream *strea
 AVRational av_guess_frame_rate(AVFormatContext *format, AVStream *st, AVFrame *frame)
 {
     AVRational fr = st->r_frame_rate;
+    const AVCodecDescriptor *desc = cffstream(st)->codec_desc;
     AVCodecContext *const avctx = ffstream(st)->avctx;
     AVRational codec_fr = avctx->framerate;
     AVRational   avg_fr = st->avg_frame_rate;
@@ -688,7 +689,7 @@ AVRational av_guess_frame_rate(AVFormatContext *format, AVStream *st, AVFrame *f
         fr = avg_fr;
     }
 
-    if (avctx->ticks_per_frame > 1) {
+    if (desc && (desc->props & AV_CODEC_PROP_FIELDS)) {
         if (   codec_fr.num > 0 && codec_fr.den > 0 &&
             (fr.num == 0 || av_q2d(codec_fr) < av_q2d(fr)*0.7 && fabs(1.0 - av_q2d(av_div_q(avg_fr, fr))) > 0.1))
             fr = codec_fr;
@@ -701,10 +702,12 @@ int avformat_transfer_internal_stream_timing_info(const AVOutputFormat *ofmt,
                                                   AVStream *ost, const AVStream *ist,
                                                   enum AVTimebaseSource copy_tb)
 {
+    const AVCodecDescriptor       *desc = cffstream(ist)->codec_desc;
     const AVCodecContext *const dec_ctx = cffstream(ist)->avctx;
     AVCodecContext       *const enc_ctx =  ffstream(ost)->avctx;
-    AVRational dec_ctx_tb = dec_ctx->framerate.num ? av_inv_q(av_mul_q(dec_ctx->framerate,
-                                                                       (AVRational){dec_ctx->ticks_per_frame, 1}))
+
+    AVRational mul = (AVRational){ desc && (desc->props & AV_CODEC_PROP_FIELDS) ? 2 : 1, 1 };
+    AVRational dec_ctx_tb = dec_ctx->framerate.num ? av_inv_q(av_mul_q(dec_ctx->framerate, mul))
                                                    : (ist->codecpar->codec_type == AVMEDIA_TYPE_AUDIO ? (AVRational){0, 1}
                                                                                                       : ist->time_base);
 
diff --git a/libavformat/demux.c b/libavformat/demux.c
index 2a32bde7f5..dec02a1a6b 100644
--- a/libavformat/demux.c
+++ b/libavformat/demux.c
@@ -213,6 +213,8 @@ FF_ENABLE_DEPRECATION_WARNINGS
         if (ret < 0)
             return ret;
 
+        sti->codec_desc = avcodec_descriptor_get(sti->avctx->codec_id);
+
         sti->need_context_update = 0;
     }
     return 0;
@@ -677,10 +679,11 @@ static void compute_frame_duration(AVFormatContext *s, int *pnum, int *pden,
             *pnum = st->time_base.num;
             *pden = st->time_base.den;
         } else if (codec_framerate.den * 1000LL > codec_framerate.num) {
-            av_assert0(sti->avctx->ticks_per_frame);
+            int ticks_per_frame = (sti->codec_desc &&
+                                   (sti->codec_desc->props & AV_CODEC_PROP_FIELDS)) ? 2 : 1;
             av_reduce(pnum, pden,
                       codec_framerate.den,
-                      codec_framerate.num * (int64_t)sti->avctx->ticks_per_frame,
+                      codec_framerate.num * (int64_t)ticks_per_frame,
                       INT_MAX);
 
             if (pc && pc->repeat_pict) {
@@ -692,7 +695,8 @@ static void compute_frame_duration(AVFormatContext *s, int *pnum, int *pden,
             /* If this codec can be interlaced or progressive then we need
              * a parser to compute duration of a packet. Thus if we have
              * no parser in such case leave duration undefined. */
-            if (sti->avctx->ticks_per_frame > 1 && !pc)
+            if (sti->codec_desc &&
+                (sti->codec_desc->props & AV_CODEC_PROP_FIELDS) && !pc)
                 *pnum = *pden = 0;
         }
         break;
@@ -1288,6 +1292,8 @@ static int read_frame_internal(AVFormatContext *s, AVPacket *pkt)
                 return ret;
             }
 
+            sti->codec_desc = avcodec_descriptor_get(sti->avctx->codec_id);
+
             sti->need_context_update = 0;
         }
 
@@ -2164,9 +2170,10 @@ static int get_std_framerate(int i)
 static int tb_unreliable(AVFormatContext *ic, AVStream *st)
 {
     FFStream *const sti = ffstream(st);
+    const AVCodecDescriptor *desc = sti->codec_desc;
     AVCodecContext *c = sti->avctx;
-    AVRational time_base = c->framerate.num ? av_inv_q(av_mul_q(c->framerate,
-                                                                (AVRational){c->ticks_per_frame, 1}))
+    AVRational mul = (AVRational){ desc && (desc->props & AV_CODEC_PROP_FIELDS) ? 2 : 1, 1 };
+    AVRational time_base = c->framerate.num ? av_inv_q(av_mul_q(c->framerate, mul))
                                             /* NOHEADER check added to not break existing behavior */
                                             : (((ic->ctx_flags & AVFMTCTX_NOHEADER) ||
                                                 st->codecpar->codec_type == AVMEDIA_TYPE_AUDIO) ? (AVRational){0, 1}
@@ -2718,13 +2725,14 @@ int avformat_find_stream_info(AVFormatContext *ic, AVDictionary **options)
                 break;
             }
             if (pkt->duration > 0) {
+                const int fields = sti->codec_desc && (sti->codec_desc->props & AV_CODEC_PROP_FIELDS);
                 if (avctx->codec_type == AVMEDIA_TYPE_SUBTITLE && pkt->pts != AV_NOPTS_VALUE && st->start_time != AV_NOPTS_VALUE && pkt->pts >= st->start_time
                     && (uint64_t)pkt->pts - st->start_time < INT64_MAX
                 ) {
                     sti->info->codec_info_duration = FFMIN(pkt->pts - st->start_time, sti->info->codec_info_duration + pkt->duration);
                 } else
                     sti->info->codec_info_duration += pkt->duration;
-                sti->info->codec_info_duration_fields += sti->parser && sti->need_parsing && avctx->ticks_per_frame == 2
+                sti->info->codec_info_duration_fields += sti->parser && sti->need_parsing && fields
                                                          ? sti->parser->repeat_pict + 1 : 2;
             }
         }
@@ -2864,15 +2872,12 @@ int avformat_find_stream_info(AVFormatContext *ic, AVDictionary **options)
                               best_fps, 12 * 1001, INT_MAX);
             }
             if (!st->r_frame_rate.num) {
-                AVRational time_base = avctx->framerate.num ? av_inv_q(av_mul_q(avctx->framerate,
-                                                                       (AVRational){avctx->ticks_per_frame, 1}))
-                                                            /* NOHEADER check added to not break existing behavior */
-                                                            : ((ic->ctx_flags & AVFMTCTX_NOHEADER) ? (AVRational){0, 1}
-                                                                                                   : st->time_base);
-                if (   time_base.den * (int64_t) st->time_base.num
-                    <= time_base.num * (uint64_t)avctx->ticks_per_frame * st->time_base.den) {
-                    av_reduce(&st->r_frame_rate.num, &st->r_frame_rate.den,
-                              time_base.den, (int64_t)time_base.num * avctx->ticks_per_frame, INT_MAX);
+                const AVCodecDescriptor *desc = sti->codec_desc;
+                AVRational mul = (AVRational){ desc && (desc->props & AV_CODEC_PROP_FIELDS) ? 2 : 1, 1 };
+                AVRational  fr = av_mul_q(avctx->framerate, mul);
+
+                if (fr.num && fr.den && av_cmp_q(st->time_base, av_inv_q(fr)) <= 0) {
+                    st->r_frame_rate = fr;
                 } else {
                     st->r_frame_rate.num = st->time_base.den;
                     st->r_frame_rate.den = st->time_base.num;
diff --git a/libavformat/internal.h b/libavformat/internal.h
index 82a79d7488..9fc980601f 100644
--- a/libavformat/internal.h
+++ b/libavformat/internal.h
@@ -23,6 +23,7 @@
 
 #include <stdint.h>
 
+#include "libavcodec/codec_desc.h"
 #include "libavcodec/packet_internal.h"
 
 #include "avformat.h"
@@ -408,6 +409,8 @@ typedef struct FFStream {
      */
     int64_t first_dts;
     int64_t cur_dts;
+
+    const AVCodecDescriptor *codec_desc;
 } FFStream;
 
 static av_always_inline FFStream *ffstream(AVStream *st)