simple change of AR

[baracus]

hi i wanted the simplest method to change the AR of a mp4 x264 file (16-9 > 4-3)

i used mediacoder since it seems the best one


now i changed that the AR in the video settings... and the file plays fine in the new AR



but the filesize is almost doubled, how come ? i only changed the the AR and it needed to re process the whole file ?


with mediacoder you cannot just change the header info without reprocessing the file?


is there a way to change the AR without the file getting bigger (in the process of reprocessing) or even just change header info`?

[Baldrick]

Mp4box. Google mp4box change aspect ratio for some command line examples.

[baracus]

can't you with eg mediacoder not JUST change the AR and leave the video (or all other video settings) itself untouched?

[Baldrick]

I have never used mediacoder. And never will.

But check if you can copy the video and ausio streams.

[Keyser]

Use Mp4Box with the following command line:

Mp4Box -par 1=PAR video.mp4

Substitute video.mp4 by the name of your video and PAR by the pixel aspect ratio calculated this way:

PAR = 4/3 * H/W ; where H = video height (pixels) and W = video width (pixels) and PAR should be in the form of N : D (withgout the spaces) where N and D are integers.

[baracus]

the problem is, if i put 4:3 it will stretch even more

goes from this to this


Width : 640 pixels
Height : 360 pixels
Display aspect ratio : 16:9


Width : 640 pixels
Height : 360 pixels
Display aspect ratio : 2.40:1

[Starbuck2010]

640x360 is a 16:9 aspect with square pixels, so I guess your video is 16:9 and you have to crop it vertically to get 4:3 aspect.

Or it's really a 4:3 footage and you should have set MediaCoder to 512x384, in that case, you just have to change AR in stream header with FFmpeg (can be done with DVDx 4.1 Free Converter but it will re-rencode).

[baracus]

it IS 4:3 FOOTAGE

can you tell me the command too? (AR CHANGE)


i read u can change it in the header AND video stream - i guess what i tried and failed (mp4box) was just the header while your suggestion is the video stream, maybe after i fix your suggestion i should retry fixing the other as well

[poisondeathray]

One way to change the bitstream AR value is to use this modified ffmpeg build in this thread
http://forum.doom9.org/showthread.php?t=152419

If you have a 640x360 square pixel video that plays with a DAR of 16:9 , but you want it to play with a DAR of 4:3

Display Aspect Ratio = Frame Aspect Ratio * Sample Aspect Ratio

4/3 = 640/360 * x/y , where x/y is the sar value or sample aspect ratio

So the value for SAR , x/y = 3:4

ffmpeg -i input.mp4 -vcodec copy -acodec copy -vbsf h264_changesps=sar=3:4 output.mp4

In general , you don't want to change both stream AR and container AR, because you might get undesirable, additive effects depending on the decoder used

[hello_hello]

In general , you don't want to change both stream AR and container AR, because you might get undesirable, additive effects depending on the decoder used

I don't understand..... if the stream and container aspect ratios are the same.......

I'm fairly sure the Bluray player in this house which supports anamorphic MKV/MP4s ignores the container aspect ratio and uses the stream aspect ratio. Or maybe it's the other way around.... I forget. By default, LAV filters gives preference to the container aspect ratio.

[poisondeathray]

Container AR is supposed to override everything , but I've seen some cases where there were multiplicative causing extreme distortions depending on the decoding chain and software used to view

There are also container inconsistencies between different containers - but I find MKV is the most consistent

[baracus]

thanks for the calculation, i would have never gotten that

i did try the 3:4 result with mp4box and it did work out !!
so unless my player will not play it i won'T even need ffmpeg


i did read somewhere else that it is advisable to change it both ways so it will not mess up



edit :
mediainfo now spits out the correct 4:3 instead of the cinema format

[baracus]

say i have a bunch of paths in a txt, can you batch process these with either mp4box or ffmpg ?

btw it says with ffmpeg:
unknown bitstream filter h264 changesps=dar=3:4

[poisondeathray]

say i have a bunch of paths in a txt, can you batch process these with either mp4box or ffmpg ?

btw it says with ffmpeg:
unknown bitstream filter h264 changesps=dar=3:4

it's sar, not dar

You need to use the modified ffmpeg build . You can rename it if you want e.g ffmpeg.roozhou.exe

Yes you can batch process a folder , But it gets trickier to do it from a text file or processing subfolders , but it should be possible as well

For one folder:

for %a in ("*.mp4") do ffmpeg -i %a -vcodec copy -acodec copy -vbsf h264_changesps=sar=3:4 %~na.new.mp4

[baracus]

it seems i still got the syntax slighty wrong... do i have to put some path somewhere?








C:\Program Files (x86)\tools\test>for %a in ("*.mp4") do "C:\Program Files (x86)
\tools\ffmpg\ar change\ffmpeg.exe" -i %a -vcodec copy -acodec copy -vbsf h264_ch
angesps=sar=3:4 %~na.new.mp4


C:\Program Files (x86)\tools\test>"C:\Program Files (x86)\tools\ffmpg\ar change\
ffmpeg.exe" -i The Jets - Crush On You (1985) - YouTube.mp4 -vcodec copy -acodec
copy -vbsf h264_changesps=sar=3:4 The Jets - Crush On You (1985) - YouTube.new.
mp4
ffmpeg version N-31792-g51fb933, Copyright (c) 2000-2011 the FFmpeg developers
built on Aug 11 2011 23:13:25 with gcc 4.5.2
configuration:
libavutil 51. 11. 1 / 51. 11. 1
libavcodec 53. 10. 0 / 53. 10. 0
libavformat 53. 6. 0 / 53. 6. 0
libavdevice 53. 2. 0 / 53. 2. 0
libswscale 2. 0. 0 / 2. 0. 0
The: No such file or directory

[poisondeathray]

Open the command prompt in the same directory as the files , and you don't need to specify the paths , except for ffmpeg.exe path . If the modified ffmpeg is in the system directory, or set up as environment variable, then you don't need to specify the ffmpeg path either . If I were you , I would rename the ffmpeg binary - so as not to confuse it with the "normal" one (in the example below I named it "ffmpeg.roozhou"

The Jets - Crush On You (1985) - YouTube.mp4

If there are spaces in your file names, you need to put the entries in quotes (for input and output)

e.g

for %a in ("*.mp4") do "PATH\ffmpeg.roozhou" -i "%a" -vcodec copy -acodec copy -vbsf h264_changesps=sar=3:4 "%~na.new.mp4"

[baracus]

thanks

thats what i did ... it was the quotes that i forgot (as you can see there are spaces in the title names)