kimvde f133766b40 Improve ffmpeg build instructions
- Simplify the supported formats configuration by moving it to a
  separate variable, therefore avoiding updating the COMMON_OPTIONS
  variable in the ffmpeg build command.
- Move the ffmpeg build command to a shell script.

PiperOrigin-RevId: 274778232
2019-10-15 23:07:45 +01:00
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2019-10-15 23:07:45 +01:00