[FFmpeg-user] With mxg/MxPEG, keyframes only are seen?

[Jesse Gordon]

Good Day,

I'm trying to use ffmpeg to convert an mxg file to a series of jpeg 
images, but ffmpeg seems to be seeing only the key frames and skipping 
the incremental/partial frames.

(mxg AKA MxPEG is a "video" format designed by Mobotix. They use it with 
their IP cameras. It uses JPEG compression, and in general functionality 
it is like mjpeg, except MxPEG also supports partial frames -- so if 
only part of the scene changes, just those jpeg blocks are updated.)

 From what I can tell, mxg is supported by ffmpeg, and when I use it, I 
do get a bunch of jpeg images, but not nearly enough. my source video 
file has a time stamp in the right top corner and with ffmpeg I get 
about 2 frames per second. However with the native mobotix camera 
software, I get about 7 frames a second.

It looks like ffmpeg is grabbing the key frames but skipping the 
"incremental" frames or whatever you want to call them. (They are not 
delta frames like real video codecs - they are just "sparse jpegs" which 
have only the needed jpeg blocks or something like that.)

The test file I'm using as a .mxg source is:
http://bookcracker.com/M00001.jpg

(Note that my test file has almost no motion in it, so the 
"delta"(sparse) frames would pretty much just contain updates for the 
timestamp in right top corner, which has mS resolution. Anyway, thus it 
makes sense that the "delta" frames would be very small, and most of the 
file size would be a result of the key frames.)

The command I'm using is:
ffmpeg -f mxg -i M00001.jpg foo-%03d.jpeg

I get 21 jpeg files, and when looking at them, the time stamp in the 
right top corner indicates that each frame is about half a second's worth.
But when playing in the Mobotix software, there are around 7 frames in 
each second.

I wish I had a way to demonstrate to you that the source file indeed has 
more than 21 frames, but I can't think of a way other than downloading 
and installing Mobotix's windows only "MxControlCenter" 
(http://www.mobotix.com/eng_US/Products/Software/MxControlCenter) but I 
wouldn't ask anyone to install a windows program anyway. But 
MxControlCenter does show all the frames; one can do "Next Frame" and 
"Prev Frame" and see each frame and there are about 7 or so frames in a 
second.

I just grabbed the latest ffmpeg and compiled yesterday:

ffmpeg -v
ffmpeg version N-46251-g54a48d2 Copyright (c) 2000-2012 the FFmpeg 
developers
   built on Oct 31 2012 15:33:44 with gcc 4.5.2 (GCC)
   configuration: --prefix=/usr
   libavutil      52.  1.100 / 52.  1.100
   libavcodec     54. 70.100 / 54. 70.100
   libavformat    54. 35.100 / 54. 35.100
   libavdevice    54.  3.100 / 54.  3.100
   libavfilter     3. 21.106 /  3. 21.106
   libswscale      2.  1.101 /  2.  1.101
   libswresample   0. 16.100 /  0. 16.100

  uname -a
Linux darkstar 2.6.37.6-smp #2 SMP Sat Apr 9 23:39:07 CDT 2011 i686 
Intel(R) Pentium(R) 4 CPU 2.80GHz GenuineIntel GNU/Linux

Here's the ffmpeg output:

ffmpeg -f mxg -i M00001.jpg foo-%03d.jpeg
ffmpeg version N-46251-g54a48d2 Copyright (c) 2000-2012 the FFmpeg 
developers
   built on Oct 31 2012 15:33:44 with gcc 4.5.2 (GCC)
   configuration: --prefix=/usr
   libavutil      52.  1.100 / 52.  1.100
   libavcodec     54. 70.100 / 54. 70.100
   libavformat    54. 35.100 / 54. 35.100
   libavdevice    54.  3.100 / 54.  3.100
   libavfilter     3. 21.106 /  3. 21.106
   libswscale      2.  1.101 /  2.  1.101
   libswresample   0. 16.100 /  0. 16.100
[mxg @ 0x8ec7520] Estimating duration from bitrate, this may be inaccurate
Guessed Channel Layout for  Input Stream #0.1 : mono
Input #0, mxg, from 'M00001.jpg':
   Duration: 00:02:56.85, start: 1351625054.845054, bitrate: 63 kb/s
     Stream #0:0: Video: mxpeg, yuvj420p, 1280x960, 1.83 tbr, 1000k tbn, 
1000k tbc
     Stream #0:1: Audio: pcm_alaw, 8000 Hz, mono, s16, 64 kb/s
Output #0, image2, to 'foo-%03d.jpeg':
   Metadata:
     encoder         : Lavf54.35.100
     Stream #0:0: Video: mjpeg, yuvj420p, 1280x960, q=2-31, 200 kb/s, 
90k tbn, 1.83 tbc
Stream mapping:
   Stream #0:0 -> #0:0 (mxpeg -> mjpeg)
Press [q] to stop, [?] for help
frame=   21 fps=0.0 q=0.0 Lsize=       0kB time=00:00:11.45 bitrate=   
0.0kbits/s dup=0 drop=35
video:2127kB audio:0kB subtitle:0 global headers:0kB muxing overhead 
-100.000000%


ls -la
-rwx------ 1 root root 1414839 Oct 30 12:24 M00001.jpg
-rwx------ 1 root root   96185 Nov  1 09:01 foo-001.jpeg
-rwx------ 1 root root   96202 Nov  1 09:01 foo-002.jpeg
-rwx------ 1 root root  119517 Nov  1 09:01 foo-003.jpeg
-rwx------ 1 root root  160964 Nov  1 09:01 foo-004.jpeg
-rwx------ 1 root root  119524 Nov  1 09:01 foo-005.jpeg
-rwx------ 1 root root  160929 Nov  1 09:01 foo-006.jpeg
-rwx------ 1 root root  184793 Nov  1 09:01 foo-007.jpeg
-rwx------ 1 root root  138074 Nov  1 09:01 foo-008.jpeg
-rwx------ 1 root root  184932 Nov  1 09:01 foo-009.jpeg
-rwx------ 1 root root  109554 Nov  1 09:01 foo-010.jpeg
-rwx------ 1 root root  138167 Nov  1 09:01 foo-011.jpeg
-rwx------ 1 root root   79951 Nov  1 09:01 foo-012.jpeg
-rwx------ 1 root root  106693 Nov  1 09:01 foo-013.jpeg
-rwx------ 1 root root   64415 Nov  1 09:01 foo-014.jpeg
-rwx------ 1 root root   79704 Nov  1 09:01 foo-015.jpeg
-rwx------ 1 root root   58068 Nov  1 09:01 foo-016.jpeg
-rwx------ 1 root root   65891 Nov  1 09:01 foo-017.jpeg
-rwx------ 1 root root   53422 Nov  1 09:01 foo-018.jpeg
-rwx------ 1 root root   58003 Nov  1 09:01 foo-019.jpeg
-rwx------ 1 root root   49175 Nov  1 09:01 foo-020.jpeg
-rwx------ 1 root root   53480 Nov  1 09:01 foo-021.jpeg

bash-4.1# ls foo-0*|wc -l
21


Am I doing it right, or what might be the problem?

Thank you very much,

Jesse Gordon