[gmail] Re: Change aspect ratio without transcoding?

[Martijn Grendelman]

On 10-04-12 10:50, Marc Leeman wrote:
>>>> I have a feeling that I'm on the wrong track here, but I'm going to ask
>>>> anyway.
>>>>
>>>> I have a MPEG-TS, containing H.264 video, in 4:3 aspect ratio. I'd like to
>>>> stretch the video to 16:9. Is that possible without transcoding, perhaps
>>>> by only remuxing?
>>>
>>> Hi, I don't know of any element that could do that on encoded video, but
>>> you could make an element yourself that only changes the
>>> pixel-aspect-ratio.
>>
>> Yes, I have been researching a way to do this.
>>
>> Using the information from [1], I should theoretically be able to replace
>> (using some for of 'binary sed') a certain byte sequence in the stream to
>> get what I want. The problem was, that I haven't been able to find the
>> sequence header ('000001B3') in the stream I was working on, so I gave it up.
>>
>> Thanks.
>>
>> [1] http://dvd.sourceforge.net/dvdinfo/mpeghdrs.html
> 
> Looks like something that could be appended to the parser; that one
> should search for the correct headers.
> 
> It might be that your stream was not properly formatted, in some cases,
> the parser corrects this. 

Another thing is, that I am not a C programmer, so writing my own or
adapting an existing plugin would not be doable for me.

If someone else want to see how feasable this would be, what I was trying
to do was the following:

- find a sequence header, identified by 000001B3 byte sequence
- within the sequence header, change the 4th byte. The highest 4 bits
represent the aspect ratio, where value of '2' means '4:3' and '3' means
'16:9'.

Best regards,
Martijn Grendelman