On Fri, Oct 14, 2022 at 05:19:44PM +0200, Andreas Rheinhardt wrote: > Peter Ross: > > Duplicates of the standard JPEG quantization tables were found in the > > AGM, MSS34(dsp), NUV and VP31 codecs. This patch elimates those duplicates, > > placing a single copy in jpegtables. > > ---
> 1. mss34dsp now uses jpegtables, yet it does not have a dependency on > it. Instead you seem to rely on all the users of mss34dsp to have a > dependency on jpegtables, yet this is not true for all of them. You will > get linking failures with --disable-everything --enable-decoder=msa1. there is a OBJS-$(CONFIG_JPEGTABLES) += line in avcodec/Makefile that takes care of this. i tested this patch under few different configurations and observed no build errors. > 2. The fact that you need to add jpegtables to configure for almost all > components that use the jpeg quant tables means that it is not really > appropriate to put the jpeg quant tables into the same files as the jpeg > huff tables. > 3. The jpeg huff tables are duplicated into libavformat for shared > builds (because the overhead of exporting them exceeds the size gains > from not duplicating them); yet when one uses --enable-shared and > --enable-static at the same time, it might be that libavformat.a is > linked to libavcodec.so and therefore has no access to libavcodec's > internal symbols like the jpegtables, so we have to duplicate the > jpegtables into libavformat.a in this case. But if one links using > libavformat.a and libavcodec.a with both containing the jpeg huffman > tables, then one will get a linker error with this patch: The jpeg > huffman tables in libavformat will be pulled in by the libavformat > component needing them. With this patch libavcodec/jpegtables.o will > also be pulled in. But it also contains the jpeg tables already provided > by lavf/jpegtables.o, so you will get a multiple definition error. > In contrast to this, before this patch, lavc/jpegtables.o would not be > pulled in, because all dependencies to the mjpeg huffman tables will be > satisfied by lavf/jpegtabes.o. > So to summarize: If one duplicates stuff in multiple libraries, the > object files must really provide the exact same symbols; not more, not less. wasn't aware jpegtabs.h was duplicated into libavformat. > The last two points imply that these tables should be moved to a file of > their own. Btw: I don't think that a configure subsystem is appropriate > for this (a single file with some tables is not really a subsystem); > actually I don't think that the current jpegtables subsystem is > appropriate at all. will do -- Peter (A907 E02F A6E5 0CD2 34CD 20D2 6760 79C5 AC40 DD6B)
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