[FFmpeg-devel] [PATCH/WIP] lavf/gif: fix timing.

[Clément Bœsch]

On Thu, Apr 18, 2013 at 03:14:43PM +0200, Clément Bœsch wrote:
> ---
> Delay between frames in GIF are expressed in ms, or 1/100.
> Unfortunately, I need to use 1/1000 and rescale manually the
> pkt->duration because they are otherwise incorrect: using
> avpriv_set_pts_info(..., 1, 100) leads to pkt->duration=1 for any rate.
> 
> Can be reproduced with -f lavfi testsrc=r={1,10,30,100...} or -r option
> with a random input.
> 
> Any idea what could cause this?
> 
> Note: patch as WIP for this reason and the required FATE update.

  19:33:53 < michaelni> ubitux, iam not sure your use of duration in the muxer is a good idea
  19:34:15 < michaelni> currently its set from ff_compute_frame_duration()
  19:34:52 < michaelni> so its not the actual durations just values based on frame rate

So delay is now done with just pkt->pts diff.

I'll apply this patch on top of the gif FATE test patch, so FATE unchanged
in the current version.

-- 
Clément B.
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From ef07177e13f6e69fd1bb46ed7adc35ae59d97587 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Cl=C3=A9ment=20B=C5=93sch?= <ubitux at gmail.com>
Date: Thu, 18 Apr 2013 15:09:37 +0200
Subject: [PATCH] lavf/gif: fix timing.

pkt->duration can not be used since the values are only based on frame
rate.
---
 libavformat/gif.c | 22 ++++++++++------------
 1 file changed, 10 insertions(+), 12 deletions(-)

diff --git a/libavformat/gif.c b/libavformat/gif.c
index 3d86f23..92a94d3 100644
--- a/libavformat/gif.c
+++ b/libavformat/gif.c
@@ -22,6 +22,7 @@
  */
 
 #include "avformat.h"
+#include "internal.h"
 #include "libavutil/avassert.h"
 #include "libavutil/imgutils.h"
 #include "libavutil/log.h"
@@ -67,6 +68,7 @@ static int gif_image_write_header(AVIOContext *pb, int width, int height,
 typedef struct {
     AVClass *class;         /** Class for private options. */
     int loop;
+    int64_t prev_pts;
 } GIFContext;
 
 static int gif_write_header(AVFormatContext *s)
@@ -89,6 +91,7 @@ static int gif_write_header(AVFormatContext *s)
     width  = video_enc->width;
     height = video_enc->height;
 
+    avpriv_set_pts_info(s->streams[0], 64, 1, 100);
     if (avpriv_set_systematic_pal2(palette, video_enc->pix_fmt) < 0) {
         av_assert0(video_enc->pix_fmt == AV_PIX_FMT_PAL8);
         gif_image_write_header(pb, width, height, gif->loop, NULL);
@@ -102,25 +105,19 @@ static int gif_write_header(AVFormatContext *s)
 
 static int gif_write_packet(AVFormatContext *s, AVPacket *pkt)
 {
-    AVCodecContext *enc = s->streams[pkt->stream_index]->codec;
+    GIFContext *gif = s->priv_data;
     AVIOContext *pb = s->pb;
-    int jiffies;
+    int duration;
+
+    duration = pkt->pts == AV_NOPTS_VALUE ? 0 : av_clip_uint16(pkt->pts - gif->prev_pts);
+    gif->prev_pts = pkt->pts;
 
     /* graphic control extension block */
     avio_w8(pb, 0x21);
     avio_w8(pb, 0xf9);
     avio_w8(pb, 0x04); /* block size */
     avio_w8(pb, 0x04); /* flags */
-
-    /* 1 jiffy is 1/70 s */
-    /* the delay_time field indicates the number of jiffies - 1 */
-    /* XXX: should use delay, in order to be more accurate */
-    /* instead of using the same rounded value each time */
-    /* XXX: don't even remember if I really use it for now */
-    jiffies = (70 * enc->time_base.num / enc->time_base.den) - 1;
-
-    avio_wl16(pb, jiffies);
-
+    avio_wl16(pb, duration);
     avio_w8(pb, 0x1f); /* transparent color index */
     avio_w8(pb, 0x00);
 
@@ -165,4 +162,5 @@ AVOutputFormat ff_gif_muxer = {
     .write_packet   = gif_write_packet,
     .write_trailer  = gif_write_trailer,
     .priv_class     = &gif_muxer_class,
+    .flags          = AVFMT_VARIABLE_FPS,
 };
-- 
1.8.2.1

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