Hi -
At the end of a 40hour encoding run I used mplex to put together the
.ac3 and new .m2v file (the .m2v file was downscaled from a HD capture).
Now I'm used to B frames being perhaps close to the size of the P
frames (with noisy material) but I do not recall ever seeing a
situation where the B frame was over 2x the size of the P frame:
INFO: [mplex] mplex version 1.6.3 (2.2.3 $Date: 2004/01/13 20:45:26 $)
INFO: [mplex] File xxx.m2v looks like an MPEG Video stream.
INFO: [mplex] File 040304015952.ac3 looks like an AC3 Audio stream.
INFO: [mplex] Video stream 0: profile 8 selected - ignoring non-standard options!
INFO: [mplex] Found 1 audio streams and 1 video streams
INFO: [mplex] Selecting dvdauthor DVD output profile
INFO: [mplex] Multiplexing video program stream!
INFO: [mplex] Scanning for header info: Video stream e0 (xxx.m2v)
INFO: [mplex] VIDEO STREAM: e0
INFO: [mplex] Frame width : 720
INFO: [mplex] Frame height : 480
INFO: [mplex] Aspect ratio : 16:9 display
INFO: [mplex] Picture rate : 29.970 frames/sec
INFO: [mplex] Bit rate : 7500000 bits/sec
INFO: [mplex] Vbv buffer size : 229376 bytes
INFO: [mplex] CSPF : 0
INFO: [mplex] Scanning for header info: AC3 Audio stream 00 (040304015952.ac3)
INFO: [mplex] AC3 frame size = 1536
INFO: [mplex] AC3 AUDIO STREAM:
INFO: [mplex] Bit rate : 49152 bytes/sec (384 kbit/sec)
INFO: [mplex] Frequency : 48000 Hz
INFO: [mplex] SYSTEMS/PROGRAM stream:
INFO: [mplex] rough-guess multiplexed stream data rate : 8056248
INFO: [mplex] target data-rate specified : 10080000
INFO: [mplex] Setting specified specified data rate: 10080000
INFO: [mplex] Run-in Sectors = 89 Video delay = 13019 Audio delay = 16022
INFO: [mplex] New sequence commences...
INFO: [mplex] Video e0: buf= 0 frame=000000 sector=00000000
INFO: [mplex] Audio bd: buf= 0 frame=000000 sector=00000000
INFO: [mplex] Scanned to end AU 678531
INFO: [mplex] STREAM e0 completed @ frame 678531.
INFO: [mplex] STREAM bd completed @ frame 707510.
INFO: [mplex] Multiplex completion at SCR=2037619126.
INFO: [mplex] Video e0: buf= 86669 frame=678531 sector=06884930
INFO: [mplex] Audio bd: buf= 13824 frame=707510 sector=00539057
INFO: [mplex] VIDEO_STATISTICS: e0
INFO: [mplex] Video Stream length: 13895055962 bytes
INFO: [mplex] Sequence headers: 45813
INFO: [mplex] Sequence ends : 1
INFO: [mplex] No. Pictures : 678532
INFO: [mplex] No. Groups : 45813
INFO: [mplex] No. I Frames : 45813 avg. size 58403 bytes
INFO: [mplex] No. P Frames : 181039 avg. size 2175 bytes
INFO: [mplex] No. B Frames : 451680 avg. size 4949 bytes
INFO: [mplex] Average bit-rate : 4910000 bits/sec
INFO: [mplex] Peak bit-rate : 8924800 bits/sec
INFO: [mplex] BUFFERING min 15 Buf max 218363
INFO: [mplex] AUDIO_STATISTICS: bd
INFO: [mplex] Audio stream length 1086736896 bytes.
INFO: [mplex] Frames : 707511
INFO: [mplex] BUFFERING min 67 Buf max 8995
INFO: [mplex] MUX STATUS: no under-runs detected.
The video looks good - but the B frames being 4949 bytes while the
P frames are 2175 bytes is a complete puzzler.
With pristine source material the B frames one would think would
be almost nothing in size. And indeed that is what the original
HD (1920x1080i) content looks like - mplex says this about the
demuxed (but otherwise original) .m2v and .ac3 files:
INFO: [mplex] mplex version 1.6.3 (2.2.3 $Date: 2004/01/13 20:45:26 $)
INFO: [mplex] File 040304015952.m2v looks like an MPEG Video stream.
INFO: [mplex] File 040304015952.ac3 looks like an AC3 Audio stream.
INFO: [mplex] Found 1 audio streams and 1 video streams
INFO: [mplex] Selecting generic MPEG2 output profile
INFO: [mplex] Multiplexing video program stream!
INFO: [mplex] Scanning for header info: Video stream e0 (040304015952.m2v)
INFO: [mplex] VIDEO STREAM: e0
INFO: [mplex] Frame width : 1920
INFO: [mplex] Frame height : 1080
INFO: [mplex] Aspect ratio : 16:9 display
INFO: [mplex] Picture rate : 29.970 frames/sec
INFO: [mplex] Bit rate : 22545600 bits/sec
INFO: [mplex] Vbv buffer size : 999424 bytes
INFO: [mplex] CSPF : 0
INFO: [mplex] Scanning for header info: AC3 Audio stream 00 (040304015952.ac3)
INFO: [mplex] AC3 frame size = 1536
INFO: [mplex] AC3 AUDIO STREAM:
INFO: [mplex] Bit rate : 49152 bytes/sec (384 kbit/sec)
INFO: [mplex] Frequency : 48000 Hz
INFO: [mplex] SYSTEMS/PROGRAM stream:
INFO: [mplex] rough-guess multiplexed stream data rate : 23410296
INFO: [mplex] target data-rate specified : 20000000
++ WARN: [mplex] Target data rate lower than computed requirement!
++ WARN: [mplex] N.b. a 20% or so discrepancy in variable bit-rate
++ WARN: [mplex] streams is common and harmless provided no time-outs will occur
INFO: [mplex] Run-in Sectors = 189 Video delay = 13934 Audio delay = 16937
INFO: [mplex] New sequence commences...
INFO: [mplex] Video e0: buf= 0 frame=000000 sector=00000000
INFO: [mplex] Audio bd: buf= 0 frame=000000 sector=00000000
INFO: [mplex] Scanned to end AU 678532
INFO: [mplex] STREAM e0 completed @ frame 678532.
INFO: [mplex] STREAM bd completed @ frame 707510.
INFO: [mplex] Multiplex completion at SCR=2037619924.
INFO: [mplex] Video e0: buf= 294743 frame=678532 sector=18239062
INFO: [mplex] Audio bd: buf= 13824 frame=707510 sector=00539860
INFO: [mplex] VIDEO_STATISTICS: e0
INFO: [mplex] Video Stream length: 36882930622 bytes
INFO: [mplex] Sequence headers: 45238
INFO: [mplex] Sequence ends : 1
INFO: [mplex] No. Pictures : 678533
INFO: [mplex] No. Groups : 45238
INFO: [mplex] No. I Frames : 45238 avg. size 51733 bytes
INFO: [mplex] No. P Frames : 180952 avg. size 23494 bytes
INFO: [mplex] No. B Frames : 452342 avg. size 500 bytes
INFO: [mplex] Average bit-rate : 13032400 bits/sec
INFO: [mplex] Peak bit-rate : 22546000 bits/sec
INFO: [mplex] BUFFERING min 15 Buf max 486325
INFO: [mplex] AUDIO_STATISTICS: bd
INFO: [mplex] Audio stream length 1086736896 bytes.
INFO: [mplex] Frames : 707511
INFO: [mplex] BUFFERING min 22 Buf max 12226
INFO: [mplex] MUX STATUS: no under-runs detected.
~13Mb/s average and the B frames are just 500 bytes!!
Something awry with mpeg2enc's B frame generation or what?
Steven Schultz
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