[xine-devel] Separate but types for two kinds of H.264? (was: Re: [xine-devel] BUF_AUDIO_AAC over demux_TS)

[Peter G. <pe...@mo...>]

Hi Miguel,

I've noticed you updates to demux_ts - quite in time since I was going 
to add them ;-)
I'd like to suggest using 2 buf types for H.264 - one for Annex B 
bytestream format, and another for NAL units. Annex B is used to enable 
NAL unit stream parsing - it adds 00 00 01 bytes before NAL unit header 
(really things are a it more complex, but in general) and makes H.264 
video stream look like people are used to see MPEG - 00 00 01 27 .... 00 
00 01 28 .... , i.e. a kind of startcodes. The startcodes are used to 
detect NALU boundaries and do not carry any useful information, thus if 
transport stream (or file format) has its own means to signal NALU 
length, it doesn't need to use Annex B - for instance, RTP may be used 
to wrap NALUs. Annex B bytestream is used in MPEG-2 TS for 0x1b stream 
type (which is H.264 video). Pure NALU stream is used by MPEG-4 ISO file 
format. Some decoders may benefit from receiveing complete NALU packets 
without any need to parse startcodes. However, parsing startcodes and 
assembleing NALUs in MPEG-2 TS demuxer may be unresonable. So probably 
it will be useful to have 2 buf types for 2 stream formats - one is 
BUF_TYPE_H264_ANNEXB, which is exactly the same as the stream appears in 
MPEG-2 TS, and another BUF_TYPE_H264_ISO, which appears in MPEG-4 ISO 
file format, and where each NALU is preced by 4 bytes of length word (a 
sample may include sevelar NALUs, and each NALU is preced by length field).

Regards,
Peter

Miguel Freitas wrote:

>
>i must admit i only understood half of what you wrote here. it would
>probably be easier to post this video somewhere so we can download and
>test it ourselves.
>
>Miguel
>
>
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