[Mp4-tech] Microsoft MPEG-4 Reference Decoder with packet loss

[Rob Koenen (MPEGIF)]

That's right. The syntax of MPEG-4 allows you to write error-resilient
decoders using the tools Steve is referring to. How you do build such
decoders is not specified in the standard - it's an area where vendors can
(and do) compete. Some decoders do not include any error robustness
processing, and may indeed fail when confronted with errors.
Best,
Rob
> -----Original Message-----
> From: Steve Wright [mailto:s.wright indigovision.com] 
> Sent: Wednesday, 7 January 2024 11:43
> To: 'Stefan A. Goor'; mp4-tech lists.mpegif.org
> Subject: RE: [Mp4-tech] Microsoft MPEG-4 Reference Decoder 
> with packet loss
> 
> 
> Hi,
> MPEG-4 provides the tools for error resilience but the 
> designer has to implement/use the tools. Maybe the MS 
> Encoder/Decoder Reference Software does not include error 
> resilience functionality?
> 
> Here at IndigoVision our hardware MPEG-4 Codec IP implements 
> Video packets with HEC and synchronization markers in the 
> encoder hardware. In the decoder we have error resync and 
> concealment in hardware and data partitioning and RVLC's in 
> software. This means our MPEG-4 Codec IP can operate over 
> lossy networks where packet loss is encountered with minimum 
> degradation of video quality to the user.
> 
> The start of a frame in MPEG-4 is marked by the VOPStartCode 
> which has a 32 bit value of 0001b6.
> 
> Hope that helps.
> 
> Steve Wright
> ASIC Manager
> IndigoVision Limited
> The Edinburgh Technopole
> Bush Loan, Edinburgh
> Scotland, UK
> EH26 0PJ
> +44 (0)131 475 7346
> +44 (0) 7780 633101 (mobile)
> +44 (0)131 475 7201 (Fax)
> http://www.indigovision.com/site/sections/products/mainstream.asp
> 
> 
> 
> 
> 
> 
> 
> -----Original Message-----
> From: mp4-tech-bounces lists.mpegif.org 
> [mailto:mp4-tech-bounces lists.mpegif.org]On Behalf Of Stefan A. Goor
> Sent: 06 January 2024 18:31
> To: mp4-tech lists.mpegif.org
> Subject: [Mp4-tech] Microsoft MPEG-4 Reference Decoder with 
> packet loss
> 
> 
> Hey All,
> Hopefully someone can help me with this.
> I have used the MPEG4IP tools to create hinted mp4 files that 
> contain mpeg4 bitstreams created with the MS Encoder 
> Reference Software and I have placed these files on the 
> Darwin Streaming Server to allow RTSP access. When I write 
> the payload of the packets received by the RTSP client to a 
> file, I can decode it with the MS Reference Decoder.  However 
> if I drop any packet, the decoder stops with a dialog box on 
> the screen that says "Debug Error!... ...abnormal program 
> termination..." and the decoder prints the following message 
> in the dos window:
> 
> 	Assertion failed: iMbType >= 0 && iMbType <= 3, file 
> d:\ms_om\sys\decoder\mbheaddec.cpp, line 476
> 
> >From what I understand, the MPEG-4 decoder should be able to handle 
> >losses
> and corruption (isn't one of the main goals of MPEG-4 to be 
> highly error resiliant?). Could anyone explain what the 
> problem may be and how I may get around it? I would like to 
> be able to decode content has been sent over a network and 
> that may have approximately 0.5% packet loss. Also, I assume 
> that each packet or at least an integer number of packets 
> corresponds to a single frame, is this true?
> >From RFC 1889 for RTP, I see that there is a marker bit that 
> generally
> indicates frame boundaries.  In MPEG-1 and 2 there was a 
> specific code that determined the start of a frame, is there 
> something similar for mpeg4 video stream? Any help with these 
> problems and questions would be greatly apreciated, Many 
> thanks, Stefan
> 
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