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Sur d’autres sites (7711)
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How do you properly free a BitStreamFilter (bsf) without getting a double free error ?
19 janvier 2021, par Alexis WilkeI'm trying to write a C++ class handling MP4 movies via ffmpeg.


First I created a couple of functions to use with
std::unique<>()so that way things get released even on exceptions.

However, I get a double free when I try to free the BitStreamFilter object, yet the documentation clearly says that each
av_bsf_alloc()must be paired with anav_bsf_free()call.



@param ctxa pointer into which the pointer to the newly-allocated context
will be written. It must be freed withav_bsf_free()after the
filtering is done.



Note : emphasis mine.


However, at the time I call the
avformat_close_input()I get a double free error, even if I haven't used the two contexts for anything !? I'm thinking that there may be a packet that both allocate and both try to free. But since these two contexts are not directly connected, I really don't understand how they end up freeing something twice.

Below is code which reproduce the error (at least on an amd64 platform). Once compiled, you can just execute it. Make sure to specify a filename as in :


./ffmpeg_demuxer_test mymovie.mp4


I used the following command to compile & link the code :


$ /usr/bin/c++ -std=c++17 -DDEBUG -D_DEBUG -D_GLIBCXX_ASSERTIONS -g -O0 \
 -fsanitize=address -fsanitize=enum -fsanitize=unreachable \
 -o ffmpeg_demuxer_test ffmpeg_demuxer_test.cpp \
 -lavformat -lavcodec


Notice the
-fsanitize=...options to capture errors such as a double free error.

Here is the code :


extern "C" {
#include <libavformat></libavformat>avformat.h>
#include <libavformat></libavformat>avio.h>
#include <libavcodec></libavcodec>avcodec.h>
}
#include <iostream>
#include <memory>


void ffmpeg_demuxer_avformat_context_free(AVFormatContext * context)
{
 if(context != nullptr) avformat_close_input(&context);
}

void ffmpeg_demuxer_av_bsf_free(AVBSFContext * context)
{
 if(context != nullptr) av_bsf_free(&context);
}


int main(int argc, char * argv [])
{
 if(argc != 2)
 {
 std::cout << "Usage: " << argv[0] << " movie.mp4" << std::endl;
 exit(1);
 }

 // init the AV libraries
 //
 av_register_all();
 avformat_network_init();

 // allocate the AVFormatContext
 //
 AVFormatContext * format_context(nullptr);
 int const r1(avformat_open_input(
 &format_context
 , argv[1]
 , nullptr // input format
 , nullptr)); // options
 if(r1 != 0
 || format_context == nullptr)
 {
 throw std::bad_alloc();
 }

 auto f_format_context = std::unique_ptr<
 AVFormatContext
 , decltype(&ffmpeg_demuxer_avformat_context_free)>(
 format_context
 , &ffmpeg_demuxer_avformat_context_free);


 // now allocate a stream
 //
 if(avformat_find_stream_info(f_format_context.get(), nullptr) < 0)
 {
 throw std::runtime_error("ffmpeg: Could not find stream info");
 }

 auto f_video_stream_index = av_find_best_stream(
 f_format_context.get()
 , AVMEDIA_TYPE_VIDEO
 , -1 // wanted stream (any)
 , -1 // related stream (none)
 , nullptr // AVCodec *
 , 0); // flags
 if(f_video_stream_index < 0)
 {
 throw std::runtime_error("ffmpeg: Could not find stream in input file");
 }
 if(static_cast<unsigned int="int">(f_video_stream_index) >= f_format_context->nb_streams)
 {
 throw std::range_error("ffmpeg: Stream index out of range");
 }

 auto f_stream = f_format_context->streams[f_video_stream_index];

 auto f_video_codec = f_stream->codecpar->codec_id;

 int f_bit_depth(0);
 switch(f_stream->codecpar->format)
 {
 case AV_PIX_FMT_YUV420P10LE:
 f_bit_depth = 10;
 break;

 case AV_PIX_FMT_YUV420P12LE:
 f_bit_depth = 12;
 break;

 default:
 f_bit_depth = 8;
 break;

 }

 bool f_mp4_h264 = f_video_codec == AV_CODEC_ID_H264 && (
 strcmp(f_format_context->iformat->long_name, "QuickTime / MOV") == 0
 || strcmp(f_format_context->iformat->long_name, "FLV (Flash Video)") == 0
 || strcmp(f_format_context->iformat->long_name, "Matroska / WebM") == 0
 );

 if(f_mp4_h264)
 {
 AVBitStreamFilter const * bsf_stream_filter(av_bsf_get_by_name("h264_mp4toannexb"));
 if(bsf_stream_filter == nullptr)
 {
 throw std::runtime_error("av_bsf_get_by_name(\"h264_mp4toannexb\") failed");
 }
 AVBSFContext * bsf_context(nullptr);
 int const r2(av_bsf_alloc(bsf_stream_filter, &bsf_context));
 if(r2 < 0
 || bsf_context == nullptr)
 {
 throw std::bad_alloc();
 }
 auto f_bsf_context = std::unique_ptr<
 AVBSFContext
 , decltype(&ffmpeg_demuxer_av_bsf_free)>(
 bsf_context
 , &ffmpeg_demuxer_av_bsf_free);
 f_bsf_context->par_in = f_stream->codecpar;
 if(av_bsf_init(f_bsf_context.get()) < 0)
 {
 throw std::runtime_error("av_bsf_init() failed");
 }
 }

 return 0;
}
</unsigned></memory></iostream>

So. Am I misreading the documentation or misusing one of the free/close function ? I don't think that the
AVBSFContextitself gets released when I close theAVFormatContext, but I may be mistaken ?

I won't put "C" as a tag since it will get removed even though this applies to C. It's not because I use C++ that I get a double free (i.e. it happens in the ffmpeg C library).


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Avoiding ffmpeg audio drift for live dash output
22 mai 2021, par mdaleHave people experienced playback drift with ffmpeg based dash segment generation ? For example :


ffmpeg -threads 2 -re -fflags +genpts -stream_loop -1 -i AVSyncTest.mp4 \
-af "aresample=async=1:min_hard_comp=0.100000:first_pts=0" \
-c:v:0 libx264 \
-pix_fmt:0 yuv420p \
-preset:0 medium \
-a53cc:0 1 \
-nal-hrd:0 cbr \
-x264opts:0 scenecut=-1:rc_lookahead=0 -b:v:0 5000k -bufsize:0 500k \
-force_key_frames:0 "expr:gte(t,n_forced*2)" \
-bf:0 8 \
-r 30 \
-c:a:0 aac -ar 48000 \
-b:a:1 96k \
-f tee -map 0:v \
-map 0:a "[f=dash:media_seg_name='chunk-stream_\$RepresentationID\$-\$Number%05d\$.mp4':init_seg_name='init-stream_\$RepresentationID\$.mp4':seg_duration=2:utc_timing_url=https\\\://time.akamai.com\\?iso:remove_at_exit=0:use_timeline=0:http_user_agent=ffmpeg_encoder.0:streaming=1:index_correction=1:timeout=1:dash_segment_type=mp4:method=PUT:http_persistent=1:adaptation_sets='id=0,streams=v\:0 id=1,streams=a' ]http://localhost:5000/out.mpd "


After a bit of playback it starts audio starts to drift. Analysis of the moof (with tools like mp4box) shows 1024 sample size with 93 Moofs with Moof->traf->default_sample_duration=1024 at 48000 sample rate giving segment duration of 1.984 seconds with every 3rd segment or so with 92 Moofs with duration of 1.962 … While each segment starts aligned ( if you reset playback you get alignment) it drifts against continuous playback.


Other examples like Akamai’s public stream. show 94 Moofs or 2.005 duration with every 3rd segment or so at the 1.984 duration. (what one would want)


Akamai’s (presumably ffmepg based) stream is averaging out to the 2s target where the above ffmpeg command is not …


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Upload video file to amazon S3 after FFMPEG conversions - Laravel
11 mai 2018, par SiddharthI’m trying to upload file to s3 using ffmpeg, and its creating a 0B file, what could be the reason behind this ?
My Code is as follows :
exec('ffmpeg -i '.config('medialibrary.s3.domain').'/listing_video/intromain.mp4'.' -vf "drawtext=fontfile='.storage_path('assets/video/FutuMd.ttf').': text='.$listing->car->name.': x=680: y=500: fontsize=55: fontcolor=white: enable=\'between(t,4,6)\'" '.Storage::put('intromainfinal.mp4', '').'');
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