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Bug de détection d’ogg
22 mars 2013, par
Mis à jour : Avril 2013
Langue : français
Type : Video
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Getting shifted timestamps when encoding a fragmented h264 mp4 with ffmpeg
14 septembre 2022, par Martin CastinI am trying to encode a fragmented h264 mp4 with ffmpeg. I tried the following command :


ffmpeg -i input.mp4 -movflags +frag_keyframe+separate_moof+omit_tfhd_offset+empty_moov output.mp4


It does give me a fragmented mp4 but the timestamps of the frames seem to be shifted by 0.04s when I read the video with mpv. The first frame has a timestamp of 0.04s instead of 0s, as in the input video (1920x1080, 50 fps). I encountered the problem both with ffmpeg 5.1 and ffmpeg 3.4.11.


I tried to add several flags, as
-avoid_negative_ts make_zeroor-copyts -output_ts_offset -0.04, but it did not help.

I am also trying to achieve this using the ffmpeg libav libraries in C++ but did not get to better result. Here are the code fragments I used.


avformat_alloc_output_context2(&oc, NULL, NULL, filename);

 if (oc_->oformat->flags & AVFMT_GLOBALHEADER) {
 codecCtx_->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
 }
...
 AVDictionary* opts = NULL;

 av_dict_set(&opts, "movflags", "frag_keyframe+separate_moof+omit_tfhd_offset+empty_moov", 0);

 ret = avformat_write_header(oc_, &opts);


Do you know how to avoid this behaviour of shifted timestamps for fragmented mp4, either with ffmpeg or libav ?


Edit : example videos and complete code example


I also tried with the following ffmpeg build


ffmpeg version 5.0.1-static https://johnvansickle.com/ffmpeg/ Copyright (c) 2000-2022 the FFmpeg developers
built with gcc 8 (Debian 8.3.0-6)
configuration: --enable-gpl --enable-version3 --enable-static --disable-debug --disable-ffplay --disable-indev=sndio --disable-outdev=sndio --cc=gcc --enable-fontconfig --enable-frei0r --enable-gnutls --enable-gmp --enable-libgme --enable-gray --enable-libaom --enable-libfribidi --enable-libass --enable-libvmaf --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librubberband --enable-libsoxr --enable-libspeex --enable-libsrt --enable-libvorbis --enable-libopus --enable-libtheora --enable-libvidstab --enable-libvo-amrwbenc --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libdav1d --enable-libxvid --enable-libzvbi --enable-libzimg
libavutil 57. 17.100 / 57. 17.100
libavcodec 59. 18.100 / 59. 18.100
libavformat 59. 16.100 / 59. 16.100
libavdevice 59. 4.100 / 59. 4.100
libavfilter 8. 24.100 / 8. 24.100
libswscale 6. 4.100 / 6. 4.100
libswresample 4. 3.100 / 4. 3.100
libpostproc 56. 3.100 / 56. 3.100


and with the sintel trailer as input video, which is 24fps, and I thus get a timeshift of 83ms. Here is the output I get.


Here is a complete code example, slightly adapted from the
muxing.cffmpeg example (audio removed and adapted for c++). This code shows exactly the same problem.

You can just comment the line 383 (that is calling
av_dict_set) to switch back to a not fragmented mp4 that will not have the timestamp shift.

/*
 * Copyright (c) 2003 Fabrice Bellard
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

/**
 * @file
 * libavformat API example.
 *
 * Output a media file in any supported libavformat format. The default
 * codecs are used.
 * @example muxing.c
 */

#include <cstdlib>
#include <cstdio>
#include <cstring>
#include <cmath>

extern "C"
{
#define __STDC_CONSTANT_MACROS
#include <libavutil></libavutil>avassert.h>
#include <libavutil></libavutil>channel_layout.h>
#include <libavutil></libavutil>opt.h>
#include <libavutil></libavutil>mathematics.h>
#include <libavutil></libavutil>timestamp.h>
#include <libavcodec></libavcodec>avcodec.h>
#include <libavformat></libavformat>avformat.h>
#include <libswscale></libswscale>swscale.h>
#include <libswresample></libswresample>swresample.h>
}

#define STREAM_DURATION 10.0
#define STREAM_FRAME_RATE 25 /* 25 images/s */
#define STREAM_PIX_FMT AV_PIX_FMT_YUV420P /* default pix_fmt */

#define SCALE_FLAGS SWS_BICUBIC

// a wrapper around a single output AVStream
typedef struct OutputStream {
 AVStream *st;
 AVCodecContext *enc;

 /* pts of the next frame that will be generated */
 int64_t next_pts;
 int samples_count;

 AVFrame *frame;
 AVFrame *tmp_frame;

 AVPacket *tmp_pkt;

 float t, tincr, tincr2;

 struct SwsContext *sws_ctx;
 struct SwrContext *swr_ctx;
} OutputStream;

static void log_packet(const AVFormatContext *fmt_ctx, const AVPacket *pkt)
{
 AVRational *time_base = &fmt_ctx->streams[pkt->stream_index]->time_base;

// printf("pts:%s pts_time:%s dts:%s dts_time:%s duration:%s duration_time:%s stream_index:%d\n",
// av_ts2str(pkt->pts), av_ts2timestr(pkt->pts, time_base),
// av_ts2str(pkt->dts), av_ts2timestr(pkt->dts, time_base),
// av_ts2str(pkt->duration), av_ts2timestr(pkt->duration, time_base),
// pkt->stream_index);
}

static int write_frame(AVFormatContext *fmt_ctx, AVCodecContext *c,
 AVStream *st, AVFrame *frame, AVPacket *pkt)
{
 int ret;

 // send the frame to the encoder
 ret = avcodec_send_frame(c, frame);
 if (ret < 0) {
 fprintf(stderr, "Error sending a frame to the encoder");
 exit(1);
 }

 while (ret >= 0) {
 ret = avcodec_receive_packet(c, pkt);
 if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
 break;
 else if (ret < 0) {
 fprintf(stderr, "Error encoding a frame\n");
 exit(1);
 }

 /* rescale output packet timestamp values from codec to stream timebase */
 av_packet_rescale_ts(pkt, c->time_base, st->time_base);
 pkt->stream_index = st->index;

 /* Write the compressed frame to the media file. */
 log_packet(fmt_ctx, pkt);
 ret = av_interleaved_write_frame(fmt_ctx, pkt);
 /* pkt is now blank (av_interleaved_write_frame() takes ownership of
 * its contents and resets pkt), so that no unreferencing is necessary.
 * This would be different if one used av_write_frame(). */
 if (ret < 0) {
 fprintf(stderr, "Error while writing output packet\n");
 exit(1);
 }
 }

 return ret == AVERROR_EOF ? 1 : 0;
}

/* Add an output stream. */
static void add_stream(OutputStream *ost, AVFormatContext *oc,
 const AVCodec **codec,
 enum AVCodecID codec_id)
{
 AVCodecContext *c;
 int i;

 /* find the encoder */
 *codec = avcodec_find_encoder(codec_id);
 if (!(*codec)) {
 fprintf(stderr, "Could not find encoder for '%s'\n",
 avcodec_get_name(codec_id));
 exit(1);
 }

 ost->tmp_pkt = av_packet_alloc();
 if (!ost->tmp_pkt) {
 fprintf(stderr, "Could not allocate AVPacket\n");
 exit(1);
 }

 ost->st = avformat_new_stream(oc, NULL);
 if (!ost->st) {
 fprintf(stderr, "Could not allocate stream\n");
 exit(1);
 }
 ost->st->id = oc->nb_streams-1;
 c = avcodec_alloc_context3(*codec);
 if (!c) {
 fprintf(stderr, "Could not alloc an encoding context\n");
 exit(1);
 }
 ost->enc = c;

 switch ((*codec)->type) {
 case AVMEDIA_TYPE_VIDEO:
 c->codec_id = codec_id;

 c->bit_rate = 400000;
 /* Resolution must be a multiple of two. */
 c->width = 352;
 c->height = 288;
 /* timebase: This is the fundamental unit of time (in seconds) in terms
 * of which frame timestamps are represented. For fixed-fps content,
 * timebase should be 1/framerate and timestamp increments should be
 * identical to 1. */
 ost->st->time_base = (AVRational){ 1, STREAM_FRAME_RATE };
 c->time_base = ost->st->time_base;

 c->gop_size = 12; /* emit one intra frame every twelve frames at most */
 c->pix_fmt = STREAM_PIX_FMT;
 if (c->codec_id == AV_CODEC_ID_MPEG2VIDEO) {
 /* just for testing, we also add B-frames */
 c->max_b_frames = 2;
 }
 if (c->codec_id == AV_CODEC_ID_MPEG1VIDEO) {
 /* Needed to avoid using macroblocks in which some coeffs overflow.
 * This does not happen with normal video, it just happens here as
 * the motion of the chroma plane does not match the luma plane. */
 c->mb_decision = 2;
 }
 break;

 default:
 break;
 }

 /* Some formats want stream headers to be separate. */
 if (oc->oformat->flags & AVFMT_GLOBALHEADER)
 c->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
}

/**************************************************************/
/* video output */

static AVFrame *alloc_picture(enum AVPixelFormat pix_fmt, int width, int height)
{
 AVFrame *picture;
 int ret;

 picture = av_frame_alloc();
 if (!picture)
 return NULL;

 picture->format = pix_fmt;
 picture->width = width;
 picture->height = height;

 /* allocate the buffers for the frame data */
 ret = av_frame_get_buffer(picture, 0);
 if (ret < 0) {
 fprintf(stderr, "Could not allocate frame data.\n");
 exit(1);
 }

 return picture;
}

static void open_video(AVFormatContext *oc, const AVCodec *codec,
 OutputStream *ost, AVDictionary *opt_arg)
{
 int ret;
 AVCodecContext *c = ost->enc;
 AVDictionary *opt = NULL;

 av_dict_copy(&opt, opt_arg, 0);

 /* open the codec */
 ret = avcodec_open2(c, codec, &opt);
 av_dict_free(&opt);
 if (ret < 0) {
 fprintf(stderr, "Could not open video codec\n");
 exit(1);
 }

 /* allocate and init a re-usable frame */
 ost->frame = alloc_picture(c->pix_fmt, c->width, c->height);
 if (!ost->frame) {
 fprintf(stderr, "Could not allocate video frame\n");
 exit(1);
 }

 /* If the output format is not YUV420P, then a temporary YUV420P
 * picture is needed too. It is then converted to the required
 * output format. */
 ost->tmp_frame = NULL;
 if (c->pix_fmt != AV_PIX_FMT_YUV420P) {
 ost->tmp_frame = alloc_picture(AV_PIX_FMT_YUV420P, c->width, c->height);
 if (!ost->tmp_frame) {
 fprintf(stderr, "Could not allocate temporary picture\n");
 exit(1);
 }
 }

 /* copy the stream parameters to the muxer */
 ret = avcodec_parameters_from_context(ost->st->codecpar, c);
 if (ret < 0) {
 fprintf(stderr, "Could not copy the stream parameters\n");
 exit(1);
 }
}

/* Prepare a dummy image. */
static void fill_yuv_image(AVFrame *pict, int frame_index,
 int width, int height)
{
 int x, y, i;

 i = frame_index;

 /* Y */
 for (y = 0; y < height; y++)
 for (x = 0; x < width; x++)
 pict->data[0][y * pict->linesize[0] + x] = x + y + i * 3;

 /* Cb and Cr */
 for (y = 0; y < height / 2; y++) {
 for (x = 0; x < width / 2; x++) {
 pict->data[1][y * pict->linesize[1] + x] = 128 + y + i * 2;
 pict->data[2][y * pict->linesize[2] + x] = 64 + x + i * 5;
 }
 }
}

static AVFrame *get_video_frame(OutputStream *ost)
{
 AVCodecContext *c = ost->enc;

 /* check if we want to generate more frames */
 if (av_compare_ts(ost->next_pts, c->time_base,
 STREAM_DURATION, (AVRational){ 1, 1 }) > 0)
 return NULL;

 /* when we pass a frame to the encoder, it may keep a reference to it
 * internally; make sure we do not overwrite it here */
 if (av_frame_make_writable(ost->frame) < 0)
 exit(1);

 if (c->pix_fmt != AV_PIX_FMT_YUV420P) {
 /* as we only generate a YUV420P picture, we must convert it
 * to the codec pixel format if needed */
 if (!ost->sws_ctx) {
 ost->sws_ctx = sws_getContext(c->width, c->height,
 AV_PIX_FMT_YUV420P,
 c->width, c->height,
 c->pix_fmt,
 SCALE_FLAGS, NULL, NULL, NULL);
 if (!ost->sws_ctx) {
 fprintf(stderr,
 "Could not initialize the conversion context\n");
 exit(1);
 }
 }
 fill_yuv_image(ost->tmp_frame, ost->next_pts, c->width, c->height);
 sws_scale(ost->sws_ctx, (const uint8_t * const *) ost->tmp_frame->data,
 ost->tmp_frame->linesize, 0, c->height, ost->frame->data,
 ost->frame->linesize);
 } else {
 fill_yuv_image(ost->frame, ost->next_pts, c->width, c->height);
 }

 ost->frame->pts = ost->next_pts++;

 return ost->frame;
}

/*
 * encode one video frame and send it to the muxer
 * return 1 when encoding is finished, 0 otherwise
 */
static int write_video_frame(AVFormatContext *oc, OutputStream *ost)
{
 return write_frame(oc, ost->enc, ost->st, get_video_frame(ost), ost->tmp_pkt);
}

static void close_stream(AVFormatContext *oc, OutputStream *ost)
{
 avcodec_free_context(&ost->enc);
 av_frame_free(&ost->frame);
 av_frame_free(&ost->tmp_frame);
 av_packet_free(&ost->tmp_pkt);
 sws_freeContext(ost->sws_ctx);
 swr_free(&ost->swr_ctx);
}

/**************************************************************/
/* media file output */

int main(int argc, char **argv)
{
 OutputStream video_st = { 0 }, audio_st = { 0 };
 const AVOutputFormat *fmt;
 const char *filename;
 AVFormatContext *oc;
 const AVCodec *audio_codec, *video_codec;
 int ret;
 int have_video = 0, have_audio = 0;
 int encode_video = 0, encode_audio = 0;
 AVDictionary *opt = NULL;
 int i;

 if (argc < 2) {
 printf("usage: %s output_file\n"
 "API example program to output a media file with libavformat.\n"
 "This program generates a synthetic audio and video stream, encodes and\n"
 "muxes them into a file named output_file.\n"
 "The output format is automatically guessed according to the file extension.\n"
 "Raw images can also be output by using '%%d' in the filename.\n"
 "\n", argv[0]);
 return 1;
 }

 filename = argv[1];

 av_dict_set(&opt, "movflags", "frag_keyframe+separate_moof+omit_tfhd_offset+empty_moov", 0);

 /* allocate the output media context */
 avformat_alloc_output_context2(&oc, NULL, NULL, filename);
 if (!oc) {
 printf("Could not deduce output format from file extension: using MPEG.\n");
 avformat_alloc_output_context2(&oc, NULL, "mpeg", filename);
 }
 if (!oc)
 return 1;

 fmt = oc->oformat;

 /* Add the audio and video streams using the default format codecs
 * and initialize the codecs. */
 if (fmt->video_codec != AV_CODEC_ID_NONE) {
 add_stream(&video_st, oc, &video_codec, fmt->video_codec);
 have_video = 1;
 encode_video = 1;
 }

 /* Now that all the parameters are set, we can open the audio and
 * video codecs and allocate the necessary encode buffers. */
 if (have_video)
 open_video(oc, video_codec, &video_st, opt);


 av_dump_format(oc, 0, filename, 1);

 /* open the output file, if needed */
 if (!(fmt->flags & AVFMT_NOFILE)) {
 ret = avio_open(&oc->pb, filename, AVIO_FLAG_WRITE);
 if (ret < 0) {
 fprintf(stderr, "Could not open '%s'\n", filename);
 return 1;
 }
 }

 /* Write the stream header, if any. */
 ret = avformat_write_header(oc, &opt);
 if (ret < 0) {
 fprintf(stderr, "Error occurred when opening output file\n");
 return 1;
 }

 while (encode_video || encode_audio) {
 /* select the stream to encode */
 if (encode_video &&
 (!encode_audio || av_compare_ts(video_st.next_pts, video_st.enc->time_base,
 audio_st.next_pts, audio_st.enc->time_base) <= 0)) {
 encode_video = !write_video_frame(oc, &video_st);
 }
 }

 av_write_trailer(oc);

 /* Close each codec. */
 if (have_video)
 close_stream(oc, &video_st);
 if (have_audio)
 close_stream(oc, &audio_st);

 if (!(fmt->flags & AVFMT_NOFILE))
 /* Close the output file. */
 avio_closep(&oc->pb);

 /* free the stream */
 avformat_free_context(oc);

 return 0;
}
</cmath></cstring></cstdio></cstdlib>

-
Audio is lost on transcoding from DTS to AAC
18 octobre 2015, par cirkoOn a Synology drive, I’m trying to transcode audio in an .MKV file from DTS to AAC using the native ffmpeg encoder. But without any error message (at least I don’t recognize any here), the audio stream is just missing in the output files. I tried it on several different files, all with the same result, leading to the conclusion that either I’m unable to see the error or something’s wrong with FFMPEG. I used the standard FFMPEG package provided with OPKG.
This is the output I usually get :CirkosDaten> ffmpeg -i encodertest.mkv -map 0 -c:v copy -c:s copy -c:a aac
-strict experimental output.mkv
ffmpeg version 2.0.2 Copyright (c) 2000-2013 the FFmpeg developers
built on Jun 3 2015 06:25:48 with gcc 4.6.4 (Marvell GCC release
20150204-c4af733b 64K MAXPAGESIZE ALIGN CVE-2015-0235)
configuration: --prefix=/usr/syno --incdir='${prefix}/include/ffmpeg'
--arch=arm --target-os=linux --cross-prefix=/usr/local/arm-marvell-linux-
gnueabi/bin/arm-marvell-linux-gnueabi- --enable-cross-compile --enable-
optimizations --enable-pic --enable-gpl --enable-shared --disable-static
--enable-version3 --enable-nonfree --enable-libfaac --enable-encoders
--enable-pthreads --disable-bzlib --disable-protocol=rtp --disable-
muxer=image2 --disable-muxer=image2pipe --disable-swscale-alpha --disable-
ffserver --disable-ffplay --disable-devices --disable-bzlib --disable-
altivec --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-
libmp3lame --disable-vaapi --disable-decoder=amrnb --disable-encoder=zmbv
--disable-encoder=dca --disable-encoder=ac3 --disable-encoder=ac3_fixed
--disable-encoder=eac3 --disable-decoder=dca --disable-decoder=eac3
--disable-decoder=truehd --cc=/usr/local/arm-marvell-linux-gnueabi/bin/arm-
marvell-linux-gnueabi-ccache-gcc
libavutil 52. 38.100 / 52. 38.100
libavcodec 55. 18.102 / 55. 18.102
libavformat 55. 12.100 / 55. 12.100
libavdevice 55. 3.100 / 55. 3.100
libavfilter 3. 79.101 / 3. 79.101
libswscale 2. 3.100 / 2. 3.100
libswresample 0. 17.102 / 0. 17.102
libpostproc 52. 3.100 / 52. 3.100
Guessed Channel Layout for Input Stream #0.1 : 5.1
Guessed Channel Layout for Input Stream #0.2 : 5.1
Input #0, matroska,webm, from 'encodertest.mkv':
Metadata:
title : encodingtest
creation_time : 2012-09-23 09:38:19
Duration: 00:01:00.94, start: 0.000000, bitrate: 9624 kb/s
Chapter #0.0: start 0.000000, end 55.347000
Metadata:
title : 00:00:00.000
Chapter #0.1: start 55.347000, end 60.936000
Metadata:
title : 00:04:56.171
Stream #0:0: Video: h264 (High), yuv420p, 1920x816 [SAR 1:1 DAR 40:17], 23.98 fps, 23.98 tbr, 1k tbn, 47.95 tbc (default)
Metadata:
title : encodingtest
Stream #0:1(ger): Audio: dts, 48000 Hz, 5.1 (default)
Metadata:
title : DTS
Stream #0:2(eng): Audio: dts, 48000 Hz, 5.1
Metadata:
title : DTS
Stream #0:3(ger): Subtitle: subrip (default)
Metadata:
title : Forced Subs
Output #0, matroska, to 'output.mkv':
Metadata:
title : encodingtest
encoder : Lavf55.12.100
Chapter #0.0: start 0.000000, end 55.347000
Metadata:
title : 00:00:00.000
Chapter #0.1: start 55.347000, end 60.936000
Metadata:
title : 00:04:56.171
Stream #0:0: Video: h264 (H264 / 0x34363248), yuv420p, 1920x816 [SAR 1:1 DAR 40:17], q=2-31, 23.98 fps, 1k tbn, 1k tbc (default)
Metadata:
title : encodingtest
Stream #0:1(ger): Subtitle: subrip (default)
Metadata:
title : Forced Subs
Stream mapping:
Stream #0:0 -> #0:0 (copy)
Stream #0:3 -> #0:1 (copy)
Press [q] to stop, [?] for help
frame= 1461 fps=528 q=-1.0 Lsize= 54636kB time=00:01:00.81 bitrate=7360.1kbits/s
video:54624kB audio:0kB subtitle:0 global headers:0kB muxing overhead
0.023249%encodingtestWhen I additionally set the bitrate, the output says
Codec AVOption b (set bitrate (in bits/s)) specified for output file #0
(output.mkv) has not been used for any stream. The most likely reason is
either wrong type (e.g. a video option with no video streams) or that it is
a private option of some encoder which was not actually used for any stream.This indicates that somehow the 5.1, 48kHz DTS stream isn’t considered as an input. Why ?
EDIT : Is it possible that DTS decoding is turned off somewhere here ? I reckoned maybe that’s why I get no errors. But I didn’t see any obvious option for that in the output.
-
ffmpeg converting video to images while video file is being written
15 octobre 2015, par user3398227Hopefully an easy question for an ffmpeg expert !
I’m currently converting large (+6GB) mpeg video into an image sequence - which is working well using the below ffmpeg command :
ffmpeg -i "input.mpeg" -vf - fps=fps=2 -f image2 -qscale 1 -s 1026x768 "output%6d.jpg"
however i have to wait for the file to finish being written to disk before i kick off ffmpeg - but this takes a good hour or so to finish writing, but what i’ve noticed is that ffmpeg can start reading the file while its being written to disk - the only snag here is it gets to the end of the file and stops before the file has finished being written...
Question is, is there a way that ffmpeg can convert to an image sequence at the same pace the video is being written (and not exit out ?)... or know to wait for the next frame to be written from the source. (unfortunately the input doesn’t support streaming, I only get a network drive and file to work off.. ) I thought i read somewhere that ffmpeg can process at the video frame rate but cant seem to find this command for love or money in the doco !!
Thanks !
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