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

Justin Ruggles justin.ruggles
Thu Aug 27 02:20:05 CEST 2009

Michael Niedermayer wrote:

> 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)

I volunteer to maintain libspeexdec.c.  David, does the ogg part look ok
to you?


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