[Mp4-tech] mp4v content in 3gp files

[Girish Shenoy]

Thanks Magnus !
As it always happens, one struggles for an answer for days and finally 
decides to write to a forum to get help. Just after that is done, one 
finds his answer.
I did not have any mp4v files. I was having a .3gp file with mp4v 
content and a .mp4 file with mp4v content.
.mp4 plays OK.
.3gp had a problem.
The answer to the problem as I discovered was simple. There seems to be 
a problem with the decoder-specific-info (the concatenated VO headers) 
in the problematic file. Just out of curiosity I just replaced the 
decoder specific info in the problematic file with the same from the 
file which was being successfully played by QT. Although in a strict 
sense, the exercise I did was outrageous, the results were pleasing. 
(Probably because the video in both files had similar properties). And 
lo!! QT started playing the file.
Now I am in the process of analyzing both decoder specific info from 
both files to get to the bottom of it. Once that happens, I guess I will 
update this thread with the root cause (if it is relevant to the members).
Btw!! thanks a lot Magnus for all that information. I was not aware of 
many of the facts you presented.
Thanks,
Girish
Magnus Hoem wrote:
> Hi Girish,
> mp4 and 3gpp are basically the same format, but there are minor  
> diifferences. In mp4 the iods-box is mandatory (if I remember  
> correctly), and it is not in 3gp. It is however not surprising that  
> QT can play both (they claim to support both, and can create both  
> types correctly). Mp4 supports mpeg4 and H264 video along with AAC  
> audio. 3gpp can also contain H263 video and AMR audio, (which is not  
> supported in mp4).
>
> About the mp4v-file. Since the release of the video-enabled iPod  
> there is some confusion about this extension. It used to be a 14496-2  
> (mpeg4) elementary stream, but now Apple uses it for a more or less  
> regular mov/3gpp-file with mpeg4 or h264 content (along with AAC  
> audio) to be played on the iPod. Which one are you refering to? I  
> think QT will have a problem playing the elementary stream, but if  
> you insert it correctly into a mov, 3gp or mp4 container it should  
> not be a problem at all. The iPod file should of course not cause a  
> problem in QT.
>
> Best regards,
> Magnus
>
> On 28 nov 2005, at 15.21, Girish Shenoy wrote:
>
>> Hi All,
>>
>> First, I note that Quicktime (and also RealPlayer) plays .mp4 files  
>> (i played some mp4 files successfully).
>> Also both these are able to play .3gp files with non-mp4 content (I  
>> played some files successfully here too).
>> In fact the 3gp file format uses the format defined my mp4 to store  
>> the mpeg-4 content.
>>
>> I noticed that I am not able to play 3gp files with mp4v content  
>> using either of the players. Quicktime gives me an error -2010  
>> "movie contains some invalid data" (quicktime player 7.0.3).
>>
>> Certain other open source (linux based) players are however able to  
>> play the same files. Theoretically any player able to play 3gp file  
>> and mp4 files should be able to play mp4v content from a 3gp  
>> file.Since both 3gp and mp4 files are essentially the same base  
>> format, I examined the mp4 file that was played successfully. The  
>> only difference I found was that this mp4 file had an additional  
>> "iods" box/atom.
>>
>> But the "iods" box/atom is not a mandatory box and in fact the 3gpp  
>> file format spec mentions that these mpeg-4 architectural elements  
>> need not be present and shall be ignored.
>>
>> Am I wrong in saying that iods is not required, is this the problem?
>> Has anyone else faced this problem? Anybody know any answers?
>>
>> I would be grateful to any information on the above.
>>
>> Thanks in advance,
>> Girish
>> _______________________________________________
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>
>
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