[FFmpeg-trac] #2789(undetermined:new): 2-pass processing of inputs, generating statistics

[FFmpeg]

#2789: 2-pass processing of inputs, generating statistics
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               Reporter:  burek      |                  Owner:
                   Type:             |                 Status:  new
  enhancement                        |              Component:
               Priority:  normal     |  undetermined
                Version:             |               Keywords:
  unspecified                        |               Blocking:
             Blocked By:             |  Analyzed by developer:  0
Reproduced by developer:  0          |
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 I would like to suggest a new feature which would first read an entire
 input file (if it is a finite source, like a file, not a live stream) and
 generate a lot of statistics, needed for the further processing requested
 on the command line.

 For example, something like this:
 {{{
 ffmpeg -generate_statistic -i input.mp4 -ss -45 -c:v copy output.mp4
 }}}
 would make a 2-pass reading of the input source. First time, it will read
 entire file, generating various statistics, one of which could be the
 number of total frames in a video stream. The second time it reads the
 input file and now it can "understand" that "-45" time point means "45
 seconds before the end", because it has got a number of total frames,
 gathered in the 1st pass.

 This would help implement other features too, which can't be easily
 implemented in a 1-pass reading of the input, which ffmpeg implements so
 far.

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Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2789>
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