ffmpeg: pass output stream duration as a hint to the muxer

Signed-off-by: Tobias Rapp <t.rapp@noa-archive.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

ffmpeg.c

@@ -2908,6 +2908,10 @@ static int init_output_stream_streamcopy(OutputStream *ost)
     if (ost->st->time_base.num <= 0 || ost->st->time_base.den <= 0)
         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);
+
     // copy disposition
     ost->st->disposition = ist->st->disposition;
 
@@ -3333,6 +3337,11 @@ static int init_output_stream(OutputStream *ost, char *error, int error_len)
         // copy timebase while removing common factors
         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->st->codec->codec= ost->enc_ctx->codec;
     } else if (ost->stream_copy) {
         ret = init_output_stream_streamcopy(ost);

libavformat/avformat.h

@@ -930,6 +930,9 @@ typedef struct AVStream {
      * Decoding: duration of the stream, in stream time base.
      * If a source file does not specify a duration, but does specify
      * a bitrate, this value will be estimated from bitrate and file size.
+     *
+     * Encoding: May be set by the caller before avformat_write_header() to
+     * provide a hint to the muxer about the estimated duration.
      */
     int64_t duration;