[FFmpeg-devel] [FFmpeg-commits] lavf: replace all uses of url_fskip with avio_seek

Måns Rullgård mans
Wed Mar 2 16:21:34 CET 2011

Peter Ross <pross at xvid.org> writes:

> On Tue, Mar 01, 2011 at 06:32:10PM +0100, Anton Khirnov  wrote:
>> Module: ffmpeg
>> Branch: master
>> Commit: e356fc57a2e9887370caec58d8aafeafd1f336dc
>> Author:    Anton Khirnov <anton at khirnov.net>
>> Committer: Ronald S. Bultje <rsbultje at gmail.com>
>> Date:      Mon Feb 28 14:57:55 2011 +0100
>> lavf: replace all uses of url_fskip with avio_seek
>> Signed-off-by: Ronald S. Bultje <rsbultje at gmail.com>
>> ---
> [..]
>>  libavformat/vocdec.c         |    8 +++---
>>  libavformat/vqf.c            |    6 ++--
>>  libavformat/wav.c            |    6 ++--
>>  libavformat/wtv.c            |   58 +++++++++++++++++++++---------------------
> Guys, the patch subject indicates what was done, but not why.
> Can somebody explain WHY the fskip convention has been replaced
> with seek. Im ignoring the original patch thread because that
> has gone political.
> This function has existed since I started using FFmpeg a decade ago.
> In all my demuxers url_fskip has been used to skip a block of unknown
> or irrelevant data. I don't 'seek' to another location in the file,
> I 'skip' over the data. The intent of the code becomes less obvious
> when fseek is used in both instances.
> Fskip has never been a problem. What possible benefit does this
> change give us? Objectively please!

This change was done in the larger context of cleaning up the
libavformat API.  Since skip() and seek(SEEK_CUR) are equivalent, we
felt there was no need to have both as actual functions in the ABI.
Some, myself included, suggested a skip() macro to simplify the code,
but Anton didn't like that for some reason.  I hope he can clarify, for
my own benefit as well as yours.

> By logical extension, the next patch in this series will be to
> universally replace get_bits1(gb) with get_bits(gb, 1). Seriously,
> why not?

That is not an accurate analogy.  get_bits1() doesn't simply call
get_bits(1), it does something more optimal.  That is not the case with
seek() vs skip().

> I am not one normally to be critical of API and broader framework
> changes, and dont have the time to read all mails, but this change,
> and the get/put_tag renaming insanity really pinches a nerve. This
> is a backward step on the master public API.
> Its really late here -- expect an avio_skip() patch from me tomorrow.

Feel free.  I see no reason to reject such a patch.

M?ns Rullg?rd
mans at mansr.com

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