fftools/ffmpeg: stop calling check_output_constraints() for streamcopy

That function only contains two checks now - whether the muxer returned
EOF and whether the packet timestamp is before requested output start
time.

The first check is unnecessary, since the packet will just be rejected
by the muxer. The second check is better combined with a related check
directly in do_streamcopy().

fftools/ffmpeg.c

@@ -976,10 +976,14 @@ static void do_streamcopy(InputStream *ist, OutputStream *ost, const AVPacket *p
         !ost->copy_initial_nonkeyframes)
         return;
 
-    if (!ost->streamcopy_started && !ost->copy_prior_start) {
+    if (!ost->streamcopy_started) {
-        if (pkt->pts == AV_NOPTS_VALUE ?
+        if (!ost->copy_prior_start &&
+            (pkt->pts == AV_NOPTS_VALUE ?
              ist->pts < ost->ts_copy_start :
-            pkt->pts < av_rescale_q(ost->ts_copy_start, AV_TIME_BASE_Q, ist->st->time_base))
+             pkt->pts < av_rescale_q(ost->ts_copy_start, AV_TIME_BASE_Q, ist->st->time_base)))
+            return;
+
+        if (of->start_time != AV_NOPTS_VALUE && ist->pts < of->start_time)
             return;
     }
 
@@ -1830,8 +1834,7 @@ static int process_input_packet(InputStream *ist, const AVPacket *pkt, int no_eo
 
     for (int oidx = 0; oidx < ist->nb_outputs; oidx++) {
         OutputStream *ost = ist->outputs[oidx];
-        if (!check_output_constraints(ist, ost) || ost->enc_ctx ||
+        if (ost->enc_ctx || (!pkt && no_eof))
-            (!pkt && no_eof))
             continue;
 
         do_streamcopy(ist, ost, pkt);