mp4 files corrupted, missing GOP format settings, any way to fix?

[smca]

Hi,

Sorry for the long story, but I think best to explain the background to this...

When I connect my Android phone to my PC (Win7), I use the standard Autoplay - "Import pictures and videos using Windows", to transfer my mp4 files across. And they were playing a-ok on the phone, which is a Sony Xperia S.

However on my PC I get a black screen during playback and no sound. Have tried various players, VLC, etc, and all the same.

The odd thing is that if I transfer the files using direct copy or other means, no problem on the PC.

So the standard Autoplay Windows import is corrupting something and I think it is the GOP format settings, whatever they are!

I've concluded this after using MediaInfo to output some stats on a good and bad mp4 of exactly the same video, then comparing the two - see below.

Why am I bothering with this? Unfortunately I have a bunch of videos that were transferred using windows import then deleted from the phone. Some were precious and trying to fix the corruption. Any help much appreciated!

Here is an excerpt of the MediaInfo outputs....

GOOD FILE
Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : Baseline@L4.0
Format settings, CABAC : No
Format settings, ReFrames : 1 frame
Format settings, GOP : M=1, N=31
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 5s 928ms
Bit rate : 19.8 Mbps
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate mode : Variable

BAD FILE
Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : Baseline@L4.0
Format settings, CABAC : No
Format settings, ReFrames : 1 frame
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 5s 928ms
Bit rate : 19.8 Mbps
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate mode : Variable

The only difference I can see looking at all the MediaInfo output is this, which is missing from the BAD one....

Format settings, GOP : M=1, N=31

Any idea what these format settings are and any way to fix?

Thanks,

Stephen

[fvisagie]

GOP means Group Of Pictures, which essentially defines the keyframe interval - how far apart keyframes are encoded. Keyframes do not require parts of other frames to be decoded; those that do are called reference frames. The shorter the keyframe interval, the more accurate and faster seeking usually is, but the output file is then usually larger.

The fact that video format differs at all between the two import processes indicates that one or both re-encoded the video in the process. Apart from introducing possible errors as you experienced, this is undesirable from a quality point of view. Unless it's done to a lossless format, re-encoding always loses picture quality. To make matters worse, you don't even seem to have control over the fact that re-encoding is done when using Windows import, let alone controlling the (quality) settings of that encode.

There are a couple of web services that atttempt to repair MP4 videos for a fee. There was a thread in this week where a name or two was mentioned, have a look. There's also a commercial DIY tool called HD Video Repair Utility in the videohelp tools section.

I don't have experience of using web services, but HD Video Repair Utility works as advertised. You give it a working and broken file. It uses the working file to orientate itself in the broken file, and then analyses it, identifying all data that have typical video and audio patterns. This is then repacked into a repaired file, optionally re-encoding that. The evaluation version is free. If you want to try it out, go through its documentation carefully. It's not complicated, but if you don't follow the correct sequence and/or don't identify the right option/s to play with, results will be sub-optimal and that would be a shame for valuable video.

Cheers,
Francois

[FireRouteR]

Hi smca,

You can easily diagnose for free your files at MP4repair.org. Repair also runs in your browser so nothing is installed on your PC. Best of luck!

--Fire

[smca]

Thanks for your replies. The videos are repairable, which is good news, but it's not cheap!

Are there any video repair tools out there that are free? The level of corruption I seem to have is minor.

I can't understand why Windows 7 would re-encode the video with the standard import utility, the files should just be copied, but something in the process is corrupting the files. This is not a one-off as keeps happening.

Somewhat frustrating but, hey ho, at least they can be repaired!

[fvisagie]

I haven't found anything that is both free and worth-while. If you want to see what HD Video Repair Utility would produce repairing one of your files in full before deciding to make the purchase, you can make your file twice as large with e.g. copy /b yourfile.mp4 + yourfile.mp4 doubleyourfile.mp4.

[smca]

Tried that but outputs two repaired files, both 50% of original video.

[smca]

Apparently v1.5 of the Video Repair Tool is freeware. Does anybody have that version they could provide a link for or email me?