[FFmpeg-devel] [PATCH 00/21] New Version

[Andreas Rheinhardt]

Here is a new version. Some of the already sent patches were slightly
modified: The first patch now removes two unused variables and "Improve
length check" has been rewritten. Furthermore, some new patches not
directly needed in order to fix the garbage error message have been
added:

1. The generic seeking code sometimes relies on the data_offset to seek
to in order to begin parsing from this point on. For the Matroska
demuxer, this field has usually been set to the beginning of the size
field of the first cluster. This is wrong, instead it should be set to
the beginning of the first cluster. This fixes a "Truncating packet of
size 21061679 to 17740959" error that one gets when using Michael's
sample with the commandline he provided.
2. Attachments are already read into a suitably padded refcounted AVBuffer,
so that one can directly reuse this AVBuffer in case this attachment
contains an attached picture.
3. The error messages in ebml_read_num were quite suboptimal and have
been fixed.

My idea to make the incremental parsing of clusters level compliant is
that levels are an EBML concept and so this should be handled internally
by the EBML functions, not the Matroska functions. So ebml_parse itself
takes care of correctly opening/closing the levels. This has been
coupled with the length checks that are done before reading an element's
payload in order to reduce the amount of checks needed. Furthermore, a
special return value is returned whenever a level is ended so that one
can use this to determine whether to perform whatever action is necessary
at the end of a level. (In the end, the actual parsing of clusters
turned out not to need this.)

This also changed the handling of unknown-sized elements: They are now
ended whenever an element not known to be allowed in them is
encountered. If we are already on level 1 and encounter an element not
known to be allowed in an unknown-sized segment, this is treated as an
indication that an error might have occured. I hope this is fine.

Dale's sample "bear-320x240-live.webm" btw has cues at the end that use
unknown-sized elements (wastefully coded on eight bytes) for CuePoints and
CueTrackPositions which is spec-incompliant. They are not referenced by
a SeekHead and so can't be used for seeking, but if they were, neither
current FFmpeg nor FFmpeg with my patches applied would be able to use
them. Are such files common (this is the first such file I ever saw)?
If so, I could probably make it work.

I have cced Steve for this (I didn't the first time, because I
thought that he (as a maintainer) would also be a subscriber to this
list).

Oh, and I did not check with Valgrind that the new lacing code doesn't
read uninitialized data. I don't even know how to use Valgrind. I just
read the code. If someone more knowledgeable than I could please test
it...

- Andreas

Andreas Rheinhardt (21):
  avformat/matroskadec: Remove unused variables
  avformat/matroskadec: Don't zero unnecessarily
  avformat/matroskadec: Get rid of cluster size field assumption
  avformat/matroskadec: Use generic size check for signed integers
  avformat/matroskadec: Set offset of first cluster
  avformat/matroskadec: Don't copy attached pictures
  avformat/matroskadec: Remove redundant initialization
  avformat/matroskadec: Improve error messages
  avformat/matroskadec: Remove non-incremental parsing of clusters
  avformat/matroskadec: Don't keep old blocks
  avformat/matroskadec: Treat SimpleBlock as EBML_BIN
  avformat/matroskadec: Remove redundant variable declaration
  avformat/matroskadec: Improve length check
  avformat/matroskadec: Use proper levels after discontínuity
  avformat/matroskadec: Redo level handling
  avformat/matroskadec: Make cluster parsing level compatible
  avformat/matroskadec: Don't reset cluster position
  avformat/matroskadec: Combine two arrays
  avformat/matroskadec: Add SilentTracks to cluster syntax
  avformat/matroskadec: Redo EOF handling
  avformat/matroskadec: Typos and cosmetics

 libavformat/matroska.h    |   1 +
 libavformat/matroskadec.c | 537 ++++++++++++++++++++------------------
 2 files changed, 280 insertions(+), 258 deletions(-)

-- 
2.19.2