avcodec: add duration field to AVCodecParserContext

This will allow parsers to export the duration of the current frame being
output, if known, instead of using AVCodecContext.frame_size.

doc/APIchanges

@@ -13,6 +13,9 @@ libavutil:   2011-04-18
 
 API changes, most recent first:
 
+2012-xx-xx - xxxxxxx - lavc 54.x.x
+  Add duration field to AVCodecParserContext
+
 2012-02-xx - xxxxxxx - lavu 51.23.1 - mathematics.h
   Add av_rescale_q_rnd()
 

libavcodec/avcodec.h

@@ -3994,6 +3994,13 @@ typedef struct AVCodecParserContext {
      * Previous frame byte position.
      */
     int64_t last_pos;
+
+    /**
+     * Duration of the current frame.
+     * For audio, this is in units of 1 / AVCodecContext.sample_rate.
+     * For all other types, this is in units of AVCodecContext.time_base.
+     */
+    int duration;
 } AVCodecParserContext;
 
 typedef struct AVCodecParser {

libavformat/utils.c

@@ -1039,6 +1039,20 @@ static int read_frame_internal(AVFormatContext *s, AVPacket *pkt)
                 if (pkt->size) {
                 got_packet:
                     pkt->duration = 0;
+                    if (st->codec->codec_type == AVMEDIA_TYPE_AUDIO) {
+                        if (st->codec->sample_rate > 0) {
+                            pkt->duration = av_rescale_q_rnd(st->parser->duration,
+                                                             (AVRational){ 1, st->codec->sample_rate },
+                                                             st->time_base,
+                                                             AV_ROUND_DOWN);
+                        }
+                    } else if (st->codec->time_base.num != 0 &&
+                               st->codec->time_base.den != 0) {
+                        pkt->duration = av_rescale_q_rnd(st->parser->duration,
+                                                         st->codec->time_base,
+                                                         st->time_base,
+                                                         AV_ROUND_DOWN);
+                    }
                     pkt->stream_index = st->index;
                     pkt->pts = st->parser->pts;
                     pkt->dts = st->parser->dts;