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

Justin Ruggles justin.ruggles
Mon Aug 24 01:16:21 CEST 2009

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.


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