The problem is that the argument 'q' is of the type uint8_t.
According to the JPEG standard, if 1 <= q <= 50, the scale factor
'S' should be 5000 / Q. Because the create_default_qtables() reuses
the variable 'q' to store the result of this calculation, for small
values of q < 19, q wil subsequently overflow and give wrong results
in the calculated quantization tables.
Instead, use a new variable 'S' (same name as in RFC2435) with the
proper range to store the result of the division.
Signed-off-by: Martin Storsjö <martin@martin.st>
Original mail and my own followup on ffmpeg-user earlier today:
I have a device sending out a MJPEG/RTP stream on a low quality setting.
Decoding and displaying the video with libavformat results in a washed
out, low contrast, greyish image. Playing the same stream with VLC results
in proper color representation.
Screenshots for comparison:
http://zevv.nl/div/libav/shot-ffplay.jpghttp://zevv.nl/div/libav/shot-vlc.jpg
A pcap capture of a few seconds of video and SDP file for playing the
stream are available at
http://zevv.nl/div/libav/mjpeg.pcaphttp://zevv.nl/div/libav/mjpeg.sdp
I believe the problem might be in the calculation of the quantization
tables in the function create_default_qtables(), the attached patch
solves the issue for me.
The problem is that the argument 'q' is of the type uint8_t. According to the
JPEG standard, if 1 <= q <= 50, the scale factor 'S' should be 5000 / Q.
Because the create_default_qtables() reuses the variable 'q' to store the
result of this calculation, for small values of q < 19, q wil subsequently
overflow and give wrong results in the calculated quantization tables. The
patch below uses a new variable 'S' (same name as in RFC2435) with the proper
range to store the result of the division.
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
* commit '4978850ca2cb1ec6908f5bc79cc592ca454d11e8':
build: Split JPEG-related tables off into a separate component
Conflicts:
configure
Merged-by: Michael Niedermayer <michaelni@gmx.at>
* commit 'bb4a310bb85f43e62240145a656b1e5285b14239':
rtpdec: Don't free the payload context in the .free function
Conflicts:
libavformat/rtpdec_latm.c
libavformat/rtpdec_mpeg4.c
libavformat/rtpdec_mpegts.c
libavformat/rtpdec_xiph.c
Merged-by: Michael Niedermayer <michaelni@gmx.at>
* commit '5d8cae45737bed6239bd6b6e0698802dbe1463c8':
rtpdec: Get rid of all trivial .alloc/.free functions
Merged-by: Michael Niedermayer <michaelni@gmx.at>
Many of these functions were named foo_free_context, and since
the functions no longer should free the context itself, only
allocated elements within it, the previous naming was slightly
misleading.
Signed-off-by: Martin Storsjö <martin@martin.st>
This makes it more consistent with depacketizers that don't have any
.free function at all, where the payload context is freed by the
surrounding framework. Always free the context in the surrounding
framework, having the individual depacketizers only free any data
they've specifically allocated themselves.
This is similar to how this works for demuxer/muxers/codecs - a
component shouldn't free the priv_data that the framework has
allocated for it.
Signed-off-by: Martin Storsjö <martin@martin.st>
* commit '90c784cc13f6bf21a8eb69f3b88b50c7a70f6c59':
rtpdec: Pass the sequence number to depacketizers
configure: Make avconv depend on null, anull and resample filters
Conflicts:
configure
Merged-by: Michael Niedermayer <michaelni@gmx.at>
* qatar/master:
dv1394: Swap the min and max values of the 'standard' option
rtpdec_vp8: Don't parse fields that aren't used
lavc: add some AVPacket doxy.
audiointerleave: deobfuscate a function call.
rtpdec: factorize identical code used in several handlers
a64: remove interleaved mode.
doc: Point to the new location of the c99-to-c89 tool
decode_audio3: initialize AVFrame
ws-snd1: set channel layout
wmavoice: set channel layout
wmapro: use AVCodecContext.channels instead of keeping a private copy
wma: do not keep private copies of some AVCodecContext fields
Conflicts:
libavcodec/wmadec.c
libavcodec/wmaenc.c
Merged-by: Michael Niedermayer <michaelni@gmx.at>
* commit '07584eaf4a95db3f11d3bc411f9786932829e82b':
mpegts: check substreams before discarding
Add a smooth streaming segmenter muxer
file: Add an avoption for disabling truncating existing files on open
img2dec: always close AVIOContexts
rtpdec_jpeg: Error out on other unsupported type values as well
rtpdec_jpeg: Disallow using the reserved q values
rtpdec_jpeg: Fold the default qtables case into an existing if statement
rtpdec_jpeg: Store and reuse old qtables for q values 128-254
rtpdec_jpeg: Simplify the calculation of the number of qtables
rtpdec_jpeg: Add more comments about the fields in the SOF0 section
rtpdec_jpeg: Clarify where the subsampling magic numbers come from
rtpdec_jpeg: Don't use a bitstream writer for the EOI marker
rtpdec_jpeg: Don't needlessly use a bitstream writer for the header
rtpdec_jpeg: Simplify writing of the jpeg header
rtpdec_jpeg: Merge two if statements
rtpdec_jpeg: Write the DHT section properly
Conflicts:
libavformat/Makefile
libavformat/allformats.c
libavformat/version.h
Merged-by: Michael Niedermayer <michaelni@gmx.at>
Everything written with this bitstream writer is 8/16 bit units
(except for a pair of 4 bit values), so using a bitstream writer
isn't necessary.
Signed-off-by: Martin Storsjö <martin@martin.st>
Generalize writing of any number of qtables. Don't manually write
16 bit values in two separate calls.
Signed-off-by: Martin Storsjö <martin@martin.st>
Currently the size header of the generated DHT section is
incorrect, making the mjpeg decoder just skip it. Since the
written huffman tables are the default ones, this failure had
gone undetected.
Signed-off-by: Martin Storsjö <martin@martin.st>
* qatar/master:
rtpdec_jpeg: Add support for default quantizers
x86: dsputil: Move specific optimization settings out of global init function
avplay: get rid of ugly casts in the options table
avplay: fix prototypes for option callbacks.
flvdec: always set AVFMTCTX_NOHEADER.
file: Use a normal private context for storing the file descriptor
configure: Adjust the xgetbv instrinsic check
configure: Add --disable-inline-asm command line option
configure: Don't try to enable the log2 function on msvcrt
Conflicts:
configure
ffplay.c
libavcodec/x86/dsputil_mmx.c
libavformat/file.c
libavformat/flvdec.c
Merged-by: Michael Niedermayer <michaelni@gmx.at>
* qatar/master:
x86: dsputil: Only compile motion_est code when encoders are enabled
mem: fix typo in check for __ICC
fate: mp3: drop redundant CMP setting
rtp: Depacketization of JPEG (RFC 2435)
Rename ff_put_string to avpriv_put_string
mjpeg: Rename some symbols to avpriv_* instead of ff_*
yadif: cosmetics
Conflicts:
Changelog
libavcodec/mjpegenc.c
libavcodec/x86/Makefile
libavfilter/vf_yadif.c
libavformat/version.h
libavutil/mem.h
Merged-by: Michael Niedermayer <michaelni@gmx.at>
