<div dir="ltr"><div>Okay, what about one of these lines in the specification?</div><div><br></div><div><5> Quantized linear predictor coefficient shift needed in bits (NOTE: this number is signed two's-complement, but should be positive, as no known encoders or decoders have support for negative shifts) <br></div><div>
<5> Quantized linear predictor coefficient shift needed in bits (NOTE: this number is signed two's-complement, but should be positive, as many decoders only support a positive value here) <br></div><div><5> Quantized linear predictor coefficient shift needed in bits (NOTE: this number is signed two's-complement, however many decoders only support a positive value) <br></div><div>
<5> Quantized linear predictor coefficient shift needed in bits (NOTE: this number is signed two's-complement, though all known decoders only support a positive value) 



</div><div><br></div><div>I just did a quick search to find open-source decoders and check them. All of them either throw an error or produce an incorrect result.<br></div><div>libFLAC, throws error: <a href="https://github.com/xiph/flac/blob/master/src/libFLAC/stream_decoder.c#L2663">https://github.com/xiph/flac/blob/master/src/libFLAC/stream_decoder.c#L2663</a><br></div><div>ffmpeg, throws error: <a href="https://github.com/FFmpeg/FFmpeg/blob/master/libavcodec/flacdec.c#L380">https://github.com/FFmpeg/FFmpeg/blob/master/libavcodec/flacdec.c#L380</a></div><div>Rockbox firmware, throws error: <a href="https://github.com/Rockbox/rockbox/blob/master/lib/rbcodec/codecs/libffmpegFLAC/decoder.c#L248">https://github.com/Rockbox/rockbox/blob/master/lib/rbcodec/codecs/libffmpegFLAC/decoder.c#L248</a></div><div>Flac.js, throws error: <a href="https://github.com/audiocogs/flac.js/blob/master/src/decoder.js#L323">https://github.com/audiocogs/flac.js/blob/master/src/decoder.js#L323</a></div><div>DrFlac, assumes positive shift: <a href="https://github.com/mackron/dr_libs/blob/master/dr_flac.h#L2958">https://github.com/mackron/dr_libs/blob/master/dr_flac.h#L2958</a></div><div>Decoder found at <a href="https://www.nayuki.io/page/simple-flac-implementation">https://www.nayuki.io/page/simple-flac-implementation</a> assumes positive shift</div><div>Flac-library-java, throws error: <a href="https://github.com/nayuki/FLAC-library-Java/blob/master/src/io/nayuki/flac/decode/FrameDecoder.java#L300">https://github.com/nayuki/FLAC-library-Java/blob/master/src/io/nayuki/flac/decode/FrameDecoder.java#L300</a></div><div>jflac, assumes positive shift: <a href="https://github.com/nguillaumin/jflac/blob/master/jflac-codec/src/main/java/org/jflac/frame/ChannelLPC.java#L77">https://github.com/nguillaumin/jflac/blob/master/jflac-codec/src/main/java/org/jflac/frame/ChannelLPC.java#L77</a></div><div>Claxon, throws error: <a href="https://github.com/ruuda/claxon/blob/aaaf40bcbfea01b6243e4699358b25b991e0727e/src/subframe.rs#L529">https://github.com/ruuda/claxon/blob/aaaf40bcbfea01b6243e4699358b25b991e0727e/src/subframe.rs#L529</a></div><div><br></div><div>Kind regards,</div><div><br></div><div>Martijn van Beurden<br></div><div><br></div><div><br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">Op vr 26 jun. 2020 om 08:57 schreef Thomas Zander <<a href="mailto:thomas.e.zander@googlemail.com">thomas.e.zander@googlemail.com</a>>:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">On Fri, 26 Jun 2020 at 05:15, Brian Willoughby <<a href="mailto:brianw@audiobanshee.com" target="_blank">brianw@audiobanshee.com</a>> wrote:<br>
<br>
> That said, there's nothing wrong with adding a note to the specification about the common implementations, particularly the reference library. Then, future developers will know both the precise specification and still have the warning that they risk incompatibility by deviating from the reference implementation.<br>
<br>
This sounds reasonable to me. The wording of this note should be very<br>
clear, though.<br>
<br>
Thomas<br>
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