[FFmpeg-user] partial file restore from tape

[Carl Eugen Hoyos]

2018-01-08 4:03 GMT+01:00 Swami Kevala <swami.kevala at ishafoundation.org>:

> We write large HD video files (MXF) to LTO tape. We want to develop a
> solution where we can restore a subclip alone from the tape. (This is
> commonly referred to as PFR - partial file restore)

(I wonder if mxf is the original format that you received the files in:
Where they maybe broadcasts in the form of transport streams
before somebody suggested to "archive" them as mxf?)

> I understand the -ss and -t options can be used to cut out a subclip - but

(The options are there to seek and trim but very generally, there
are files where seeking is difficult.)

> this is only when the entire file is on disk.

(I wonder if this is true.)

> Using our tape software we can restore a certain subsection of the file
> (based on a byte offset, and byte length). I want to know if we can use
> ffmpeg to convert this into a playable file.

The question is very general (and we do have mxf samples for which
this would definitely be possible) but I believe in the general sense, you
cannot use FFmpeg to do this, you have to write your own mxf demuxer
that reads the file header and tells your tape software what to get from
the tape. This would not be true if your files were transport streams
(as I wonder they originally were, see above).

I may be missing something and you may only need a new protocol to
access the tape.

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Carl Eugen