[FFmpeg-devel] [PATCH] Set correct frame_size for Speex decoding

Michael Niedermayer michaelni
Mon Aug 24 03:53:37 CEST 2009

On Sun, Aug 23, 2009 at 07:16:21PM -0400, Justin Ruggles wrote:
> Justin Ruggles wrote:
> > Michael Niedermayer wrote:
> > 
> >> On Sun, Aug 16, 2009 at 10:01:53PM -0400, Justin Ruggles wrote:
> >>> Michael Niedermayer wrote:
> >>>
> >>>> On Sun, Aug 16, 2009 at 12:26:32PM -0400, Justin Ruggles wrote:
> >>>>> Michael Niedermayer wrote:
> >>>>>
> >>>>>> On Sun, Aug 16, 2009 at 05:07:18PM +0200, Michael Niedermayer wrote:
> >>>>>>> On Sat, Aug 15, 2009 at 07:55:46PM -0400, Justin Ruggles wrote:
> >>>>>>>> Michael Niedermayer wrote:
> >>>>>> [...]
> >>>>>>>>>>> what exactly is the argument you have that speex should not be handled like
> >>>>>>>>>>> every other codec?!
> >>>>>>>>>>> split it in a parser, the muxer muxes ONLY a single speex packet per
> >>>>>>>>>>> container packet. Any extension from that is low priority and "patch welcome"
> >>>>>>>>>>> IMHO ...
> >>>>>>>>>> The downside for Speex is the container overhead since individual frames
> >>>>>>>>>> are very small.
> >>>>>>>>> this is true for many (most?) speech codecs
> >>>>>>>>>
> >>>>>>>>> also if we write our own speex encoder, it will only return one frame at a
> >>>>>>>>> time.
> >>>>>>>> Why would it have to?  
> >>>>>>> because the API requires it, both encoders and decoders have to implement the
> >>>>>>> API, a video encoder also cannot return 5 frames in one packet.
> >>>>>>> APIs can be changed but you arent arguing for a API change you argue for
> >>>>>>> ignoring the API and just doing something else.
> >>>>>>>
> >>>>>>>
> >>>>>>>> If the user sets frame_size before initialization
> >>>>>>>> to a number of samples that is a multiple of a single frame, it could
> >>>>>>>> return multiple speex frames at once, properly joined together and
> >>>>>>>> padded at the end.  With libspeex this is very easy to do because the
> >>>>>>>> functionality is built into the API.
> >>>>>>>>
> >>>>>>>> I understand the desire to keep what are called frames as separate
> >>>>>>>> entities, but in the case of Speex I see it as more advantagous to allow
> >>>>>>>> the user more control when encoding.  If frames are always split up,
> >>>>>>>> this limits the users options for both stream copy *and* for encoding to
> >>>>>>>>  just 1 frame per packet.
> >>>>>>>>
> >>>>>>>> If you're dead-set against this idea, then I will finish the parser that
> >>>>>>>> splits packets in order to continue with my other Speex patches, but I
> >>>>>>>> don't like how limiting it would be for the user.
> >>>>>>> i am againt speex handling things different than other speech codecs
> >>>>>>> based on arguments that apply to other speech codecs as well.
> >>>>>>> Also iam against passing data between muxer and codec layers in a way
> >>>>>>> that violates the API.
> >>>>>> ffmpeg seperates muxer and codec layers, writing a demuxer & decoder
> >>>>>> that depend on things beyond the API (frames per frame) is going to
> >>>>>> break things. We had similar great code (passing structs in AVPacket.data
> >>>>>> because it was convenient) that also didnt turn out to be that great
> >>>>>> and required a complete rewrite ...
> >>>>>>
> >>>>>>
> >>>>>> ive alraedy said nut doesnt allow multiple frames per packet, but its
> >>>>>> not just nut, avi as well doesnt allow multiple frames per packet
> >>>>>> for VBR and either way avi needs to have its headers set up properly,
> >>>>>> not with fake frame size and such and flv as we alaredy know has a 
> >>>>>> issue with >8 frames per frame. All that is just what we know of will
> >>>>>> break if you implement your hack, what else will break is something we
> >>>>>> only would learn after some time.
> >>>>>>
> >>>>>> IMHO, demuxer->parser->splited frames [unless it is not possible to split]
> >>>>>> if a muxer can store multiple frames it can merge several depending on its
> >>>>>> abilities and user provided parameters, that merging could also be done
> >>>>>> as a bitstream filter.
> >>>>>> But just skiping the spliting and merging and hoping that every container
> >>>>>> would allow anyting that any other container allowed is just not going to
> >>>>>> work. And even more so as we already know of many combinations that would
> >>>>>> noz work
> >>>>> I do understand your point.  There is a subtle difference with speex
> >>>>> though.  The process of merging of frames into groups of frames is
> >>>>> something that is specified by the codec itself, not the container.  To
> >>>>> the container, it would be as transparent as for an audio codec that
> >>>>> allows different numbers of samples/duration for a frame.  Nut would
> >>>>> support it just fine, as it does with FLAC with different numbers of
> >>>>> samples per frame.  As for FLV, it would be the same as if it doesn't
> >>>>> allow over a certain number of samples per frame before getting choppy
> >>>>> and/or crashing.
> >>>> hmmm, could you quote the part of the speex spec that supports your view?
> >>>> and provide a link to that spec. (iam asking for a quote instead of just
> >>>> url cuz of the ML archive ...)
> >>> unfortunately there is not a speex specification per-se, but a speex
> >>> manual that gives some hints and guidance.  the libspeex code is
> >>> definitive reference.
> >>>
> >>> http://speex.org/docs/manual/speex-manual/node7.html
> >>>
> >>> "Sometimes it is desirable to pack more than one frame per packet (or
> >>> other basic unit of storage). The proper way to do it is to call
> >>> speex_encode $ N$  times before writing the stream with speex_bits_write.
> >>>
> >>> In cases where the number of frames is not determined by an out-of-band
> >>> mechanism, it is possible to include a terminator code. That terminator
> >>> consists of the code 15 (decimal) encoded with 5 bits, as shown in Table
> >>> 4. Note that as of version 1.0.2, calling speex_bits_write automatically
> >>> inserts the terminator so as to fill the last byte. This doesn't
> >>> involves any overhead and makes sure Speex can always detect when there
> >>> is no more frame in a packet."
> >>>
> >>> The end of the packet is able detected because it looks like the start
> >>> of another frame, but the mode id is the terminator code.  This is
> >>> needed because a full valid speex frame can be only 5 bits.
> >>>
> >>> What happens when libspeex writes frames is this:
> >>> If all the combined frames end on a byte boundary, no terminator code is
> >>> used because the packet data will end at the end of a frame.  If the
> >>> combined frames do not end on a byte boundary, a 0-bit followed by
> >>> enough 1's to pad to the next byte are appended.  The result is that if
> >>> there are 5 or more bits, the terminator code will be detected.
> >> iam not truely happy about all that but i agree that its overall alot
> >> more convenient and simpler to keep these bit packed pieces of bull shit
> >> together but in that case it has to be considered that this is a whole
> >> frame and all variables have to be set accordingly.
> > 
> > It is definitely a lot simpler.  I agree it's ugly, but it all works out
> > ok if we're consistent in the encoder, decoder, and all muxers and
> > demuxers supporting speex.  I'll send a new patch sometime soon with
> > more documentation about how speex frames are to be handled throughout
> > FFmpeg.
> New patch attached.

any volunteers who want to maintain libspeexdec.c ?
oggparsespeex.c is alraedy maintained by david
(no i dont want to maintain codecs that are desgned like that)

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Complexity theory is the science of finding the exact solution to an
approximation. Benchmarking OTOH is finding an approximation of the exact
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