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

Justin Ruggles justin.ruggles
Fri Aug 28 02:49:02 CEST 2009

Michael Niedermayer wrote:

> On Wed, Aug 26, 2009 at 08:20:05PM -0400, Justin Ruggles wrote:
>> 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
> then please add yoursef to MAINTAINERS, unless you alraedy did


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