Author Topic: chopped audio in downloaded video, problem... and solution  (Read 389 times)

Brookline

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chopped audio in downloaded video, problem... and solution
« on: September 01, 2019, 10:15:14 PM »
maybe this could help somebody...
problem:
recently i downloaded a video .flv (h264 25fps aac 44100) and my goal was to convert it in mpg dvd.
the problem was the audio in flv file is chopped: it stops each .5s then restarts! very unfair! After mpg conversion, same problem in the mpg.
Curiously video and audio in the chopped video are allways corresponding; that means the video also is chopped...
see the picture ''chopped audio - audacity'' , 2 mn sample (i saved the audio file from flv to wav file with avidemux then opend this wav with audacity). i will try to join this wav/mp3 5s sample file but i m not sure it is possible on this forum.
you will find 2 mn of the flv video,after be converted to mpeg with avidemux so you can see / hear the problem at the link https://we.tl/t-KYTsAl7U0Q (link validity only one week, sorry).
I tried many tests during several hours and no result ( i tried a special software cutting all blanks in a video in one time but that did not work...)
Solution:
after that i had the idea to convert the chopped flv video in other format than mpg.
i converted the flv to mkv with avidemux very simply: copy, audio copy, mkv wuxer... the result was MAGIC! audio and video are normal in the mkv.
After i converted the mkv to mpg/dvd and the mpg was also completly ''clean''.




eumagga0x2a

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Re: chopped audio in downloaded video, problem... and solution
« Reply #1 on: September 02, 2019, 03:42:47 AM »
Please provide admlog.txt (compress it as zip if necessary) from loading unaltered source video (.flv, may be MP4 as well) in Avidemux.


Brookline

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Re: chopped audio in downloaded video, problem... and solution
« Reply #2 on: September 02, 2019, 02:29:44 PM »
here is the admlog of the flv file, i hope it is the one you are asking for.

eumagga0x2a

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Re: chopped audio in downloaded video, problem... and solution
« Reply #3 on: September 02, 2019, 05:12:15 PM »
Are you really using Avidemux v2.6.21? May I ask, why? Handling of SBR (spectral band replication) in AAC has been much improved since then.

Please retry with a supported version (which is always the latest nightly or at least the latest release – for Windows it is now 2.7.5 VC++ which is 2.7.4 VC++ with build environment fixes).

Brookline

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Re: chopped audio in downloaded video, problem... and solution
« Reply #4 on: September 03, 2019, 08:37:17 PM »
Hello eumagga0x2a,
you are right. i tried 2.7.5 VC++ and flv video and mpg conversion are o k. i give you the admlog 2 7 5 (flv with 2 mn mpg conversion, in zip folder. I hope it is possible to join a zip folder).
i agree i m not very excited to install new versions. Sure new version is improved version. however sometime any applications are downgraded. you probably will be horrified (sorry...) if i tell you i use still often use 2.5.6-1 avidemux! I have a good reason for that (i think). I often do snapshots / save frame picture to jpg. To do that i need two things:
1- to see frame by frame, forward and BACKWARD. Even VLC is not able to do that (in mpg videos)
2- to have a normal size window. Very often after video opening the picture is or too large or too narrow. Scarlett Johansson s face is like Laurel or Hardy... To correct this i use resize and go to output view .
The problem with last avidemux versions is that it is not possible to go frame by frame if you are in the output view. it is possible to see the output in normal reading but as soon as you stop you return to input view. With 2.5.6-1 version, you stay in outpput view after stop...
However i will keep 2.7.5 VC++...  but also 2.5.6-1...
thank you for your attention and sorry if this post is a few long and maybe a few ''out subject''...

eumagga0x2a

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Re: chopped audio in downloaded video, problem... and solution
« Reply #5 on: September 03, 2019, 09:26:20 PM »
Why do you re-encode H.264 to MPEG-2, a vastly inferior codec?

I often do snapshots / save frame picture to jpg. To do that i need two things:
1- to see frame by frame, forward and BACKWARD. Even VLC is not able to do that (in mpg videos)

Of course Avidemux is able to do that (Avidemux even quite speedy with video cache set to maximum of 16 decoded pictures). mpv is able to do that too. Both are restricted by the very nature of video compression, i.e. to go backward, you need to go all the way back to the previous keyframe and decode from there. Once the cache is empty, we have to repeat the whole procedure.

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2- to have a normal size window. Very often after video opening the picture is or too large or too narrow. Scarlett Johansson s face is like Laurel or Hardy...

This is called anamorphic video. Avidemux by design always uses square pixel for display, after all it is not a video player but a tool to edit video.

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To correct this i use resize and go to output view .
The problem with last avidemux versions is that it is not possible to go frame by frame if you are in the output view.

Right, as video filters may modify timing and number of frames. It is very hard or impossible to seek to a particular frame other than starting over from the very beginning.

However, in current Avidemux versions you can apply filters when saving frames as JPEG, e.g. the swsResize filter. While the display will be squeezed, this can be compensated in the exported JPEG image.

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With 2.5.6-1 version, you stay in outpput view after stop...

Well, this worked because it just counted frames, this design simply didn't work with modern codecs and often led to loss of A/V sync.

Brookline

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Re: chopped audio in downloaded video, problem... and solution
« Reply #6 on: September 05, 2019, 11:51:51 AM »
Hello eumagga0x2a,
thank you for the infomations.
1-Why do i re-encode H.264 to MPEG-2: because i watch the videos only on my tv with my dvd player, a top model one, doing frame by frame forward and backward and allowing to continue a dvd at an exact time. And as you know the dvd format is mpg and ac3... I do an iso with astodvd (probably not the best but i am now used to) who makes also the dvd menu . then only to write the iso on a dvd.  I record also the tv on an other dvd player with HDD but to save place on the HDD i record in 352/576! I agree, it is not high definition. but recording high definition and play it on a tv is not very easy (for me). And i am born with the black and white tv... My eyes are now formatted to...
2- what do you call ''video cache''? is that a part of my windows 7-64 or it is in avidemux?
Thank you for the mpv information. It s very kind of you! I did not know it. I could test only a few minutes but seems to do what i wish. I tried 10th of players... the only one able to do total frame by frame  i found is ''avs dvd player''. And he does snapshots. but it is now about 10 years old and seems to be limited to mpeg (no flv, mp4, mkv...) but for my mpgs it works. Only it seems the picture quality is poor so i prefer to do the snapshots with avidemux 2 5 who has no problem with mpg.
3- i agree avidemux 2 5 does not work today with many formats/ codecs and high definition... So i am using now the latest versions ( a problem which blocked me a long time was in ''mpg2ff, configure, encoding 2 pass video size, target video size XXX. ) if the xxx value is too high, the conversion does not work. message ''file not correctly saved ''... I e for a 3 mn mpg video, normal size about 50 mb, if i left 700  or i put 200 for xxx it does not work. I think there is a reason for that but now i know the problem ant pay attention to it.
Thank you again.

eumagga0x2a

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Re: chopped audio in downloaded video, problem... and solution
« Reply #7 on: September 05, 2019, 03:29:42 PM »
1-Why do i re-encode H.264 to MPEG-2: because i watch the videos only on my tv with my dvd player, a top model one, doing frame by frame forward and backward and allowing to continue a dvd at an exact time.

Unless the TV set is really an ancient one and doesn't support high definition and can't decode H.264 on its own, this looks as a pretty bad choice for me.

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I do an iso with astodvd (probably not the best but i am now used to) who makes also the dvd menu . then only to write the iso on a dvd.  I record also the tv on an other dvd player with HDD but to save place on the HDD i record in 352/576!

These procedures make me shiver.

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2- what do you call ''video cache''? is that a part of my windows 7-64 or it is in avidemux?

In Avidemux "Edit" --> "Preferences" --> "Output" --> "Caching of decoded pictures" --> "Cache size". The minimum value is 8, the maximum (the default one) 16. This setting allows to reduce cache size on systems with constrained resources (e.g. an integrated graphics with very little memory).