Add support for mdat-only 3GP

[jsd]

Many cell phone cameras are now producing 3gp files with no moov atoms, only mdat. Right now ffmpeg can't do anything with them.

$ ffmpeg -i 12423.3gp
ffmpeg version git-N-29818-gb7c7f89, Copyright (c) 2000-2011 the FFmpeg developers

built on May 11 2011 15:23:54 with gcc 4.1.2 20080704 (Red Hat 4.1.2-48)
configuration: --enable-gpl --enable-libfaac --enable-libmp3lame --enable-libx264 --enable-pthreads --enable-static --disable-shared --disable-network --enable-nonfree --extra-ldflags=-static
libavutil 51. 2. 1 / 51. 2. 1
libavcodec 53. 5. 0 / 53. 5. 0
libavformat 53. 0. 3 / 53. 0. 3
libavdevice 53. 0. 0 / 53. 0. 0
libavfilter 2. 5. 0 / 2. 5. 0
libswscale 0. 14. 0 / 0. 14. 0

[mov,mp4,m4a,3gp,3g2,mj2 @ 0x8e64a60] moov atom not found
12423.3gp: Operation not permitted

Support for this format would be great.

Sample file available at:

 http://videoupload.thismoment.com.s3.amazonaws.com/mdat-only.3gp

[cehoyos]

Which program opens the file?
(QuickTime? doesn't)

[cehoyos]

Please re-open this ticket if a program can be found that plays the sample.