[FFmpeg-devel] [PATCH 23/24] ffmpeg: simplify the use of OutputStream.frame_number

[Anton Khirnov]

It features in limiting the number of output frames (-frames option) and
currently can be incremented from two places:
- for video encoding (not streamcopy), in do_video_out() after each
  successful avcodec_send_frame() call
- for all other cases, in of_submit_packet()

Not only is this inconsistent and confusing, but also the special
treatment for video encoding is redundant, since
AVCodecContext.frame_count stores the exact same value (number of
successful avcodec_send_frame()) calls.

Replace the use of OutputStream.frame_count in do_video_out() with
AVCodecContext.frame_count. Modify OutputStream.frame_count in the same
way for all streams.
---
 fftools/ffmpeg.c     |  9 ++++-----
 fftools/ffmpeg_mux.c | 19 +++++++------------
 2 files changed, 11 insertions(+), 17 deletions(-)

diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
index 538601e440..aff3cc350e 100644
--- a/fftools/ffmpeg.c
+++ b/fftools/ffmpeg.c
@@ -1031,7 +1031,7 @@ static void do_video_out(OutputFile *of,
 
         switch (ost->vsync_method) {
         case VSYNC_VSCFR:
-            if (ost->frame_number == 0 && delta0 >= 0.5) {
+            if (enc->frame_number == 0 && delta0 >= 0.5) {
                 av_log(NULL, AV_LOG_DEBUG, "Not duplicating %d initial frames\n", (int)lrintf(delta0));
                 delta = duration;
                 delta0 = 0;
@@ -1039,7 +1039,7 @@ static void do_video_out(OutputFile *of,
             }
         case VSYNC_CFR:
             // FIXME set to 0.5 after we fix some dts/pts bugs like in avidec.c
-            if (frame_drop_threshold && delta < frame_drop_threshold && ost->frame_number) {
+            if (frame_drop_threshold && delta < frame_drop_threshold && enc->frame_number) {
                 nb_frames = 0;
             } else if (delta < -1.1)
                 nb_frames = 0;
@@ -1069,7 +1069,7 @@ static void do_video_out(OutputFile *of,
      * But there may be reordering, so we can't throw away frames on encoder
      * flush, we need to limit them here, before they go into encoder.
      */
-    nb_frames = FFMIN(nb_frames, ost->max_frames - ost->frame_number);
+    nb_frames = FFMIN(nb_frames, ost->max_frames - enc->frame_number);
     nb0_frames = FFMIN(nb0_frames, nb_frames);
 
     memmove(ost->last_nb0_frames + 1,
@@ -1081,7 +1081,7 @@ static void do_video_out(OutputFile *of,
         nb_frames_drop++;
         av_log(NULL, AV_LOG_VERBOSE,
                "*** dropping frame %d from stream %d at ts %"PRId64"\n",
-               ost->frame_number, ost->st->index, ost->last_frame->pts);
+               enc->frame_number, ost->st->index, ost->last_frame->pts);
     }
     if (nb_frames > (nb0_frames && ost->last_dropped) + (nb_frames > nb0_frames)) {
         if (nb_frames > dts_error_threshold * 30) {
@@ -1222,7 +1222,6 @@ static void do_video_out(OutputFile *of,
             }
         }
         ost->sync_opts++;
-        ost->frame_number++;
 
         if (vstats_filename && frame_size)
             do_video_stats(ost, frame_size);
diff --git a/fftools/ffmpeg_mux.c b/fftools/ffmpeg_mux.c
index e97ec8ab93..c3666fbba1 100644
--- a/fftools/ffmpeg_mux.c
+++ b/fftools/ffmpeg_mux.c
@@ -200,23 +200,18 @@ static void write_packet(OutputFile *of, OutputStream *ost, AVPacket *pkt)
 
 void of_submit_packet(OutputFile *of, AVPacket *pkt, OutputStream *ost)
 {
-    AVStream *st = ost->st;
     int ret;
 
     /*
-     * Audio encoders may split the packets --  #frames in != #packets out.
-     * But there is no reordering, so we can limit the number of output packets
-     * by simply dropping them here.
-     * Counting encoded video frames needs to be done separately because of
-     * reordering, see do_video_out().
+     * Limit the number of output frames by dropping any excess packets.
+     * This should not trigger for video encoding, which due to possible
+     * reordering needs to be treated specially - see do_video_out().
      */
-    if (!(st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO && ost->encoding_needed)) {
-        if (ost->frame_number >= ost->max_frames) {
-            av_packet_unref(pkt);
-            return;
-        }
-        ost->frame_number++;
+    if (ost->frame_number >= ost->max_frames) {
+        av_packet_unref(pkt);
+        return;
     }
+    ost->frame_number++;
 
     if (of->mux->header_written) {
         write_packet(of, ost, pkt);
-- 
2.33.0