fftools/ffmpeg_mux: set stream duration after the timebase is certainly known

Stop assuming the encoder knows the muxing timebase, which does not
always have to hold (e.g. due to bitstream filters).

fftools/ffmpeg_enc.c

@@ -445,10 +445,6 @@ int enc_open(OutputStream *ost, AVFrame *frame)
     if (ost->st->time_base.num <= 0 || ost->st->time_base.den <= 0)
         ost->st->time_base = av_add_q(ost->enc_ctx->time_base, (AVRational){0, 1});
 
-    // copy estimated duration as a hint to the muxer
-    if (ost->st->duration <= 0 && ist && ist->st->duration > 0)
-        ost->st->duration = av_rescale_q(ist->st->duration, ist->st->time_base, ost->st->time_base);
-
     ost->mux_timebase = enc_ctx->time_base;
 
     ret = of_stream_init(of, ost);

fftools/ffmpeg_mux.c

@@ -666,6 +666,11 @@ int of_stream_init(OutputFile *of, OutputStream *ost)
     if (ret < 0)
         return ret;
 
+    if (ms->stream_duration) {
+        ost->st->duration = av_rescale_q(ms->stream_duration, ms->stream_duration_tb,
+                                         ost->st->time_base);
+    }
+
     ost->initialized = 1;
 
     return mux_check_init(mux);

fftools/ffmpeg_mux.h

@@ -69,6 +69,9 @@ typedef struct MuxStream {
      * used for making up missing dts values */
     int64_t last_mux_dts;
 
+    int64_t    stream_duration;
+    AVRational stream_duration_tb;
+
     // audio streamcopy - state for av_rescale_delta()
     int64_t ts_rescale_delta_last;
 

fftools/ffmpeg_mux_init.c

@@ -914,10 +914,6 @@ static int streamcopy_init(const Muxer *mux, OutputStream *ost)
             ost->st->time_base = av_add_q(av_stream_get_codec_timebase(ost->st), (AVRational){0, 1});
     }
 
-    // copy estimated duration as a hint to the muxer
-    if (ost->st->duration <= 0 && ist->st->duration > 0)
-        ost->st->duration = av_rescale_q(ist->st->duration, ist->st->time_base, ost->st->time_base);
-
     if (!ms->copy_prior_start) {
         ms->ts_copy_start = (mux->of.start_time == AV_NOPTS_VALUE) ?
                             0 : mux->of.start_time;
@@ -1283,6 +1279,12 @@ static OutputStream *ost_add(Muxer *mux, const OptionsContext *o,
             exit_program(1);
     }
 
+    // copy estimated duration as a hint to the muxer
+    if (ost->ist && ost->ist->st->duration > 0) {
+        ms->stream_duration    = ist->st->duration;
+        ms->stream_duration_tb = ist->st->time_base;
+    }
+
     return ost;
 }