[PART.SOLVED] Changing the pixel aspect ratio + cropping without re-encode

[falco2000]

[I edited the title of this thread. Please read post #5 for my crop-related question and post #13 for my latest question, again about aspect ratio change]

Hello everybody.

Do you know if it's possible to modify the pixel aspect ratio of an MP4 (h.264) movie without totally re-encoding it?

I'm not talking about setting this parameter in the movie player during the playback of the movie.

I'd just like to change the aspect ratio information inside the MP4 file without touching anything else. Almost a video stream copy: no recalculation of pixels, no recompression and bitrate changes. Just the aspect ratio.

Is it possible?

Thank you very much for your help.

PS: the movie is encoded with constant quality (i.e.: variable bitrate).

[DB83]

Why ?

[poisondeathray]

yes you can eg. mp4box (eg. yamb is a gui you can use)

[falco2000]

yes you can eg. mp4box (eg. yamb is a gui you can use)

Wow, I just tried it now and it just does what I wanted. Thank you so much Poisondeathray, really!

Thanks thanks thanks

[falco2000]

A new problem came up: is it possible to also crop the movie without re-encoding it?

I mean the same as above, almost a video stream copy: no recalculation of pixels, no recompression and bitrate changes. Just discarding the pixels that don't belong to the area that I want to crop.

Can any program do that?

[Baldrick]

Nope. Cropping requires reencoding.

[poisondeathray]

You can try this modifed ffmpeg build . But in my experience it's buggy, most operations don't work as advertised - but it does have a "lossless" crop parameter

http://forum.doom9.org/showthread.php?t=152419

So basically what Baldrick said ^

[Selur]

But in my experience it's buggy, most operations don't work as advertised

a good thing might be to report those bugs to the author,..

[poisondeathray]

But in my experience it's buggy, most operations don't work as advertised

a good thing might be to report those bugs to the author,..

Most of them have been reported

1088=>1080 (which is the standard crop for h.264) works fine, everything else doesn't work well (well actually you're limited to <16)

This isn't a "true" crop. It modifies a flag so the decoder crops

[Baldrick]

Didn't know that you could change crop flags....but it looks like it isn't that useful yet.

[Selur]

problem is, it's just a flag that most decoders simply ignore,..
(btw. mkv also has such a flag on the container level which might be more supported,..)

[falco2000]

Ok thanks you all anyway

[falco2000]

I need to change the DAR or PAR of an MKV movie that I converted applying a wrong aspect ratio. Poisondeathray told me here the way to do that for MP4 movies, but what about MKV ones?

Thank you very much.

[jagabo]

MMG (part of MkvToolNix) lets you set the AR flags in the MKV header. But not all players obey the flags in the header, MP4 or MKV.

h264 AR Changer lets you change the SAR flags in the h.264 stream. But it can't add SAR flags to a stream that doesn't already have them. It's not hosted at this site because several malware scanners flag it.

[falco2000]

MMG (part of MkvToolNix) lets you set the AR flags in the MKV header. But not all players obey the flags in the header, MP4 or MKV.

Thank you very much Jagabo, I'll use MMG.