[FFmpeg-trac] #6596(avformat:new): G726 codec suspected to not comply with ITU standard
FFmpeg
trac at avcodec.org
Fri Aug 18 11:22:59 EEST 2017
#6596: G726 codec suspected to not comply with ITU standard
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Reporter: | Type: defect
alban.meffre | Priority: critical
Status: new | Version: git-
Component: avformat | master
Keywords: G726 ITU | Blocked By:
standard compliance | Reproduced by developer: 0
Blocking: |
Analyzed by developer: 0 |
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the G726 codec ffmpeg implementation seems not to comply with ITU standard
below are the files and commands needed to perform verification
*** test vectors ***
original test vectors from the ITU in ASCII format
(https://www.itu.int/net/itu-t/sigdb/speaudio/Gseries.htm)
NRM.M : the test input vector encoded in mu law (sample rate 8kHz, mono)
RN24FM.I : the expected result , unpacked to right justified codes
input_mulaw.bin : binary version of the above NRM.M input file
input_mulaw.wav : playable version
$ ffmpeg -f mulaw -ar 8000 -i input_mulaw.bin -acodec copy input_mulaw.wav
*** encoding with ITU compliant G726 encoder ***
g726encode.exe : g726 encoder from the ITU-T user's group on software
tools
output_g726.bin : output result
$ g726encode.exe -3 -u -i input_mulaw.bin -o output_g726.bin
*** binary comparison between output and ITU test vector ***
RN24FM.bin : bit packed binary version of the above RN24FM.I file
!!!!!! these two file's contents are identical -> g726encode.exe IS ITU
compliant !!!!!!
*** decode and listen to the result ***
output_g726_decoded_pcm_s16le.bin : decoded result of g726encode.exe
$ g726decode.exe -3 -l -i output_g726.bin -o
output_g726_decoded_pcm_s16le.bin
this file can be played correctely -> g726decode.exe IS ITU compliant too
$ ffplay -f s16le -ar 8000 output_g726_decoded_pcm_s16le.bin
*** encoding with ffmpeg and listen to the result ***
output_g726_ffmpeg.bin : ffmpeg g726 encode output result
output_g726_ffmpeg.wav : ffmpeg g726 encode output result (playable)
$ ffmpeg -f mulaw -ar 8000 -i input_mulaw.bin -acodec g726 -code_size 3
output_g726_ffmpeg.wav
$ ffmpeg -f mulaw -ar 8000 -i input_mulaw.bin -acodec g726 -code_size 3 -f
u8 output_g726_ffmpeg.bin
output_g726_ffmpeg_decoded_pcm_s16le.bin : decoded result of
output_g726_ffmpeg.bin
$ g726decode.exe -3 -l -i output_g726_ffmpeg.bin -o
output_g726_ffmpeg_decoded_pcm_s16le.bin
!!!!!! this file cannot be played correctely -> ffmpeg's implementation of
the g726 codec is not compliant with ITU !!!!!!
$ ffplay -f s16le -ar 8000 output_g726_ffmpeg_decoded_pcm_s16le.bin
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Ticket URL: <https://trac.ffmpeg.org/ticket/6596>
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