# Fixing broken videos

Post iPhone launch, in this new age, it is common to carry a device capable of capturing high definition images and videos. Most people today carry a high end device capable of capturing video/audio, in the form of a Mobile Phone. This has made us raise our expectation that we should capture most moments, if not all.

But as is with everything, sometimes things ditch you right at the moment when you did not want it to. In new age phones, scenarios usually are: you capturing a video and the actual data not written to the disk (battery drain, cpu overheat, software bug: Whatever). Such was my case from the year 2012, where one of the videos was corrupt. Corrupt as in, A/V not in sync.

Now everytime I solve a real world problem using Free Software tools, I feel the need to express my gratitude. It also serves as a note for me (and maybe others too), for future, if I run into similar problems. ;-)

So as it turns out (in layman terms), a video clip is nothing but 2 streams: Video and Audio. Now most video run at 30 frames per second. And the audio stream synchronizes with the video frames. Sorry, I did not read up beyond that, as I was able to fix my problem.

So, my thought was that the video stream is not corrupt. It just is rendering at a slower frame rate. So, there were 2 problems. 1: Video rendering slower than the usual 30 fps rate. 2: As a result of 1, audio not being in sync with video.

Thanks to gpac tools, even a novice, I was able to quickly separate the streams. And then re-encode the video stream into 30 fps. And then merge the audio + video stream together. And the result: Just awesome.

In below steps, Strip the video which results in a raw H264 data file. Similar for audio. And then just re-encode the streams, specifying the framerate.

_MP4Box -add 20121002_164608.mp4#video -raw 1 -new test1_

test1_track1.h264

_MP4Box -add 20121002_164608.mp4#audio -raw 2 -new test1_audio_

test1_audio_track2.aac

_MP4Box -add test1_track1.h264:fps=30 -add test1_audio_track2.aac -new test1_audio_30fps.mp4_