Andreas Rheinhardt 458d0dea90 lavf/webm_chunk: Fix NULL dereference ...

The earlier version of the webm_chunk muxer had several bugs:

1. If the first packet of an audio stream didn't have a PTS of zero,
then no chunk will be started before a packet is delivered to the
underlying Matroska/WebM muxer, i.e. the AVFormatContext used to write
these packets had a NULL as AVIOContext for output. This is behind the
crash in ticket #5752.

2. If an error happens during writing a packet, the underlyimg
Matroska/WebM muxer context is freed. This leads to a use-after-free
coupled with a double-free in webm_chunk_write_trailer (which supposes
that the underlying AVFormatContext is still valid).

3. Even when no error occurs at all, webm_chunk_write_trailer is still
buggy: After the underlying Matroska/WebM muxer has written its trailer,
ending the chunk implicitly flushes it again which is illegal at this
point.

These bugs have been fixed.

Fixes #5752.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
(cherry picked from commit 8c6ee7626b)
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

2020-07-01 22:10:02 +02:00

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