[FFmpeg-devel] [PATCH v2] fftools/ffmpeg: accelerate seeking while reading input at native frame rate

[Linjie Fu]

From: Linjie Fu <linjie.justin.fu at gmail.com>

Skip the logic of frame rate emulation until the input reaches the
specified start time.

Test CMD:
   $ffmpeg -re -ss 30 -i input.mp4 -pix_fmt yuv420p -f sdl2 -

Before the patch:
first time to got frame, it takes 257305 us
After this patch:
first time to got frame, it takes 48879 us

Signed-off-by: Linjie Fu <linjie.justin.fu at gmail.com>
---
[v2]: fixed the mixed declaration and code warning
Calculate the time to get the first frame:
https://github.com/fulinjie/ffmpeg/commit/2aa4762e1e65709997b1ab9dd596332244db80ed
 fftools/ffmpeg.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
index e97d879cb3..c8849e4250 100644
--- a/fftools/ffmpeg.c
+++ b/fftools/ffmpeg.c
@@ -4221,10 +4221,14 @@ static int get_input_packet(InputFile *f, AVPacket **pkt)
 {
     if (f->rate_emu) {
         int i;
+        int64_t pts;
+        int64_t now;
         for (i = 0; i < f->nb_streams; i++) {
             InputStream *ist = input_streams[f->ist_index + i];
-            int64_t pts = av_rescale(ist->dts, 1000000, AV_TIME_BASE);
-            int64_t now = av_gettime_relative() - ist->start;
+            if (!ist->got_output)
+                continue;
+            pts = av_rescale(ist->dts, 1000000, AV_TIME_BASE);
+            now = av_gettime_relative() - ist->start;
             if (pts > now)
                 return AVERROR(EAGAIN);
         }
-- 
2.31.1