[Libav-user] Reuse of format context after free and reallocate?

Tue Mar 16 21:56:27 EET 2021

I found the issue I was freeing the codecs (audio and video) before the format context was being freed.  Simple removing the avcodec_free_context() calls from before the format context free fixes the issue.

Thanks
________________________________
From: william keeling <williamkeeling at hotmail.com>
Sent: Wednesday, March 3, 2021 8:42 PM
To: This list is about using libavcodec, libavformat, libavutil, libavdevice and libavfilter. <libav-user at ffmpeg.org>
Subject: Re: [Libav-user] Reuse of format context after free and reallocate?

Again, Thanks for your input -- never said the code was bug free or even not buggy -- but I do know the free of all the context listed are being called and other than avformat_free_context() which has no way to check it worked  (not sure way it was written like that) are validated.

code is here https://github.com/wkeeling63/racecam

Please let me know if you have any ideas

Thanks

________________________________
From: Libav-user <libav-user-bounces at ffmpeg.org> on behalf of Paul B Mahol <onemda at gmail.com>
Sent: Wednesday, March 3, 2021 1:28 PM
To: This list is about using libavcodec, libavformat, libavutil, libavdevice and libavfilter. <libav-user at ffmpeg.org>
Subject: Re: [Libav-user] Reuse of format context after free and reallocate?

On Wed, Mar 3, 2021 at 8:26 PM william keeling <williamkeeling at hotmail.com<mailto:williamkeeling at hotmail.com>> wrote:
thanks for you input -- I am freeing all context and still get the errors as if FLVContext is not freed

Than show actual code, It must be buggy.

________________________________
From: Libav-user <libav-user-bounces at ffmpeg.org<mailto:libav-user-bounces at ffmpeg.org>> on behalf of Paul B Mahol <onemda at gmail.com<mailto:onemda at gmail.com>>
Sent: Wednesday, March 3, 2021 11:21 AM
To: This list is about using libavcodec, libavformat, libavutil, libavdevice and libavfilter. <libav-user at ffmpeg.org<mailto:libav-user at ffmpeg.org>>
Subject: Re: [Libav-user] Reuse of format context after free and reallocate?

On Wed, Mar 3, 2021 at 5:50 PM william keeling <williamkeeling at hotmail.com<mailto:williamkeeling at hotmail.com>> wrote:
I have not used "valgrind" I will need to look into that tool.  any tips on how to use it?

If you are on Linux, using it is very easy.

yes, I am free the all contexts before reallocation but I cannot find a way to for the FLVContext/Muxer to be freed/reinitialized thru the API.
I am doing the following:

avcodec_free_context() of all streams video and audio

avformat_free_context()

avio_close()

If you really do all this than that error would never happen.

________________________________
From: Libav-user <libav-user-bounces at ffmpeg.org<mailto:libav-user-bounces at ffmpeg.org>> on behalf of Paul B Mahol <onemda at gmail.com<mailto:onemda at gmail.com>>
Sent: Wednesday, March 3, 2021 5:54 AM
To: This list is about using libavcodec, libavformat, libavutil, libavdevice and libavfilter. <libav-user at ffmpeg.org<mailto:libav-user at ffmpeg.org>>
Subject: Re: [Libav-user] Reuse of format context after free and reallocate?

On Wed, Mar 3, 2021 at 5:22 AM william keeling <williamkeeling at hotmail.com<mailto:williamkeeling at hotmail.com>> wrote:
 I did some digging and found the error is coming from this code in flvenv.c line 921.

  if (pkt->dts < -flv->delay) {
        av_log(s, AV_LOG_WARNING,
               "Packets are not in the proper order with respect to DTS\n");
        return AVERROR(EINVAL);

flv is a pointer to  FLVContext from AVFormatContext->priv_data.

Looks like the avformat_write_header()/avformat_init_output uses the state of the muxer at the last run even if the AVFormatContext has been freed and reallocated.
So how do I get the FLVContext to be initlized as if a fresh run. Or how do I free the old FLVContext so when avformat_write_header() initlizes the priv_data it is fresh.
________________________________
From: Libav-user <libav-user-bounces at ffmpeg.org<mailto:libav-user-bounces at ffmpeg.org>> on behalf of william keeling <WilliamKeeling at hotmail.com<mailto:WilliamKeeling at hotmail.com>>
Sent: Monday, March 1, 2021 2:32 PM
To: libav-user at ffmpeg.org<mailto:libav-user at ffmpeg.org> <libav-user at ffmpeg.org<mailto:libav-user at ffmpeg.org>>
Subject: [Libav-user] Reuse of format context after free and reallocate?

I have a program the creates flash format stream and is work the first time thru but when I process the second stream, I get DTS/PTS non monotonically errors.

After each stream I free and reallocate all contexts:

avcodec_free_context() of all streams video and audio

avformat_free_context()

avio_close()

What am I missing so the format context can be reallocate and used?

Looks like to be real bug to me.

Thanks William

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