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• How to fix duration for an incompletely downloaded video ?

  15 octobre 2017, par Krash

  I am partially downloading a video by specifying the Ranges header. I am doing this in python. So, suppose there is video whose duration is 4:43 min and has size 2.56 mb and I am only downloading 1 mb of it, so the actual duration of the video is somewhere around the 2 min mark. Now when I play this video, it plays till it has downloaded but shows 4:43 still as its total duration and abruptly ends like a corrupted video file does. Is there a way I can edit the bytes I receive on downloading the file, so that the video player recognises the exact position after which it should end ?

  More importantly, I want to know if in videos, the start and end is determined by some set of bytes ? Like, if I download a video from the 3000th byte to 6000th byte, it won’t play as if its a corrupt video, so I want to know if its possible to add some bytes to the beginning of the file to let the player know that this is the beginning. How does a video player determine the end duration of a video from just the bytes ?

• Convert a Video_TS dir to a single mp4 or mkv file ?

  29 août 2018, par RocketNuts

  I’ve got a file-to-file copy from a DVD, consisting of a Video_TS directory with a bunch of BUP, IFO and VOB files. I can open some (not all) of these files in a player like VLC, and it seems to contain fragments of the movie but it appears like garbage. As if the encoding or file structure is corrupted.

  However, if I open the entire Video_TS dir with VLC, it plays fine.

  Is there a way to convert this Video_TS dir to one single video file, such as an MP4 or MKV ?

  I’ve read about the possibility of binary concatenating the VOB files, and I tried that, but to no avail. Also I wouldn’t know how to the determine the exact order of the VOB files, and more importantly that information must be within the files itself somehow (considering that video players can play it automatically).

  (edit) Someone edited the question and removed the ffmpeg part. Sorry if I didn’t clarify this further : I’m actually explicitly looking for a way to do this with ffmpeg (from shell, on macOS).

• How to handle differing .mp4 file types from different sources ?

  10 octobre 2017, par Dave502619

  If I take a .mp4 recorded on my mobile (Samsung S5) and pass it through FFmpeg with the below command, the output file (fileX.avi) is a greyscale bitmap uncompressed video file.

  • The offset values in fileX.avi (output from FFmpeg) to allow me to locate the video frame data are always 5680 bytes for the file header.

  • And 62 bytes for the inter frame header.

  • The data is uncompressed RGB24 so i can easily calculate the size of a video frame from height x width x 3.

  So my C# application can access the video frames in fileX.avi always at these above offsets.
  (This works great).

  My FFmpeg Command is :

  ffmpeg.exe -i source.mp4 -b 1150 -r 20.97 -g 120 -an -vf format=gray -f rawvideo -pixfmt gray -s 384x216 -vcodec rawvideo -y fileX.avi

  However... I recently took an .mp4 file from a different source (produced by Power Director 14 instead of direct from my mobile phone) and used this as the input source.mp4. But now the structure of fileX.avi differs as the offset values of 5680 + 62 bytes from the start in fileX.avi do not land me at the start of the video data frames.

  There seems to be different file formats for .mp4 - and obviously if there are my crude offset approach will not work for them all. I suspected at the time I wrote the code my method was all too easy a solution !

  So can anyone advise on the approach I should take now ? Should I check the original .mp4 or the output file (fileX.avi) to determine a "file type" to which I can determine the different offsets ?

  At the very least I need to be able to identify the "type" of .mp4 file that works so I can declare the type that will work with my software.