Fix crash when a stream codec is unknown, in particular fix trac
ticket #1243.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

Improve overall consistency, allow some factorization.

A duration value is undefined when is 0, take into consideration this
fact when printing optional fields.

This is for interoperability purpose with the fork.

Make writer_print_chapter_header() set the internal values *before* the
private writer callback is called, otherwise the accessed internal values
will be wrong.

Fix regression introduced in fa6cb2fd.

Found-By: Daemon404

Liberally based on the work of Luca Barbato <lu_zero@gentoo.org>, done
for libav/avprobe.

Move the field "multiple_entries" from the JSON writer private context to
WriterContext, and rename it "multiple_sections".

This allows to factorize the code with the pending INI format patch.

Avoid to specify implementation details, better to check the code for
that.

Signed-off-by: Stefano Sabatini <stefasab@gmail.com>

The special-case behavior may complicate parsing when the
-show_format_entry option is used programmatically in a script.

The option default=nk=1 achieves the same purpose, if the objective is to
skip printing the single field key.

Fix warning:
ffprobe.c: In function ‘probe_file’:
ffprobe.c:1576:14: warning: unused variable ‘i’ [-Wunused-variable]

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

Also remove the unused print_fmt_opt() in the process.

Help simplifying parsing in certain cases.

The option is useful for simplifying parsing.

Also use the new option in fate, in order to fix the regression
introduced by the previous commit.

Do not skip chapter header/footer printing, which breaks the parsing for
most writers.

The function was introduced in 653d117c, but is not required.

Fixes sporadic decode failures and trac ticket #997.

Simplify, increase robustness.

Signed-off-by: Stefano Sabatini <stefasab@gmail.com>

Signed-off-by: Stefano Sabatini <stefasab@gmail.com>

The index for the binary_unit_prefixes array is expected to be positive,
so avoid to use negative indexes for accessing it.