lavf: make compute_pkt_fields2() return meaningful error values

Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavformat/utils.c

@@ -2867,7 +2867,7 @@ static int compute_pkt_fields2(AVFormatContext *s, AVStream *st, AVPacket *pkt){
             pkt->pts, pkt->dts, st->cur_dts, delay, pkt->size, pkt->stream_index);
 
 /*    if(pkt->pts == AV_NOPTS_VALUE && pkt->dts == AV_NOPTS_VALUE)
-        return -1;*/
+        return AVERROR(EINVAL);*/
 
     /* duration field */
     if (pkt->duration == 0) {
@@ -2902,11 +2902,11 @@ static int compute_pkt_fields2(AVFormatContext *s, AVStream *st, AVPacket *pkt){
         av_log(s, AV_LOG_ERROR,
                "Application provided invalid, non monotonically increasing dts to muxer in stream %d: %"PRId64" >= %"PRId64"\n",
                st->index, st->cur_dts, pkt->dts);
-        return -1;
+        return AVERROR(EINVAL);
     }
     if(pkt->dts != AV_NOPTS_VALUE && pkt->pts != AV_NOPTS_VALUE && pkt->pts < pkt->dts){
         av_log(s, AV_LOG_ERROR, "pts < dts in stream %d\n", st->index);
-        return -1;
+        return AVERROR(EINVAL);
     }
 
 //    av_log(s, AV_LOG_DEBUG, "av_write_frame: pts2:%"PRId64" dts2:%"PRId64"\n", pkt->pts, pkt->dts);