What's this bbMPEG error mean?

[absinthe]

Oftentimes when muxing, after bbMPEG scans the files but just before muxing, it will show something to the effect of "data rate may be too low for mux rate; watch for PTS/DS underflows" (that may not be it exactly).

What does this mean?

-abs

[Trahald]

6972 is the maxmimum svcd mux rate where 6972 is in 50 byte/sec units, so the maximum combined video/audio mux rate in bps is 2788800 (6972x50x8). each sector is 2324 bytes and at a mux rate of 348600 bytes/sec (6972x50), 150 (348600/2324) sectors/second are read. out of the 2324 bytes of a sector a minimum of 22 bytes (pack header+PES header) are needed for muxing overhead. so the minimum muxing overhead is 26400 bps (22x8x150). svcd also specifies that the sequence headers start at the beginning of a PES packet. what this means is that if a sequence header was going to fall into the middle of a sector, the bytes remaining in the sector should be filled with a padding packet and the sequence header would then be placed at the beginning of the PES packet in the next sector. the unused bytes in this sector (now a padding packet) are wasted but they still count in the total bitrate. in a 15/3 GOP structure at 29.97fps there are 2 sequence headers every second, so assume the case where a 1/2 of the bytes of two sectors are wasted, this yields 18592 bps additional muxing overhead. 2788800 - 26400 - 18592 = 2743808bps maximum combined video/audio bitrate to avoid pts/dts muxing errors assuming your encoder is accurate enough. remember to calculate bitrates correctly i.e. 2600 video is 2662400bps (2600x1024), 128 audio is 131072bps

snippit i found on the net. basicaly people advise to use 0 so bbmpeg will figure it out itself. i usually just try larger numbers until it takes.. sometimes it asks you to increase audio delay as well.. bbmpeg is good about warning you

[absinthe]

Thanks. I was always advised to use 0 when hanging around the kvcd forums, but I thought that had something to do with that particular format. But if it will work for basically any (S)VCD, I'll start doing that.

-abs