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  1. Hello

    I have the following 3hour/12GB video that I'd like to compress further so it's about 1GB:

    Container : MPEG-PS
    Duration: 03:02:14.36, start: 0.226767, bitrate: 9463 kb/s
    Stream #0:0[0x80]: Audio: ac3, 48000 Hz, 5.1(side), s16, 448 kb/s
    Stream #0:1[0x1e0]: Video: mpeg2video (Main), yuv420p, 720x576 [SAR
    64:45 DAR 16:9], 25 fps, 25 tbr, 90k tbn, 50 tbc

    This when played in VLC has no sound/no video (Ffmpeg N-46469-gc995644):
    Code:
    ffmpeg -i input.mpg -ss 0 -t 30 -c:v libx264 -vf scale=iw/2:-1 -preset faster -c:a copy output.mpg
    Even this sample has no sound/no video:

    Code:
    ffmpeg -i input.mpg -ss 0 -t 30 -c:v copy -c:a copy output.sample.mpg
    Does someone know of a no-brainer tool for Windows that could do the job?

    Thank you.
    Last edited by yetanotherlogin; 18th Nov 2012 at 08:11.
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  2. Member DB83's Avatar
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    Compress to what ?

    You could NEVER compress a 3 hr mpg2 down to a1 gig mpg2.

    autogk could give you an xVID but it sure will not look great.
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  3. Member hech54's Avatar
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    You couldn't create an iPod video to look good from 12GB to 1GB.
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  4. I'm a MEGA Super Moderator Baldrick's Avatar
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    Output as mkv or mp4 in ffmpeg instead.
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  5. Thanks for the help. Quality is not an issue, as it's just a conference to show to people who couldn't be there.

    This worked:
    Code:
    ffmpeg -i input.mpg -c:v libx264 -vf scale=iw/2:-1 -preset faster -c:a copy output.mp4
    I read that libx264 is a better codec than mpeg2, but out of curiosity, why should I use MP4 or MKV as container instead of MPEG-PS?
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  6. Member DB83's Avatar
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    Quality (in the video sense) may not be an issue but the end-user would still expect to be able to see it.

    The 'container' is just that. It contains the compressed video. In your latest example you have a more efficient codec ie h264 rather than mpeg2 which you can not reasonably compress below 3-4000 kbps. You still end up with a 5-6 gb vid.

    But do the full 3 hour vid. I am sure you still will struggle to get that down to 1 gb.
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  7. Halfway-through, the file is 400MB, so it should be about 800MB. Stay tuned for the quality check.

    Edit: Works fine. Video is 360x288 25fps.

    Thanks everyone.
    Last edited by yetanotherlogin; 18th Nov 2012 at 08:02.
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  8. Member DB83's Avatar
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    Originally Posted by yetanotherlogin View Post
    Halfway-through, the file is 400MB, so it should be about 800MB. Stay tuned for the quality check.

    Edit: Works fine. Video is 360x288 25fps.

    Thanks everyone.
    Pls post a mediainfo report of the new file. It may work fine but it sure do not look right from where I sit.
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  9. There's no desync between audio/video and the definition is good enough for watching, considering it's just people in a conference.

    Code:
    Format                                   : MPEG-4
    Format profile                           : Base Media
    Codec ID                                 : isom
    File size                                : 781 MiB
    Duration                                 : 3h 2mn
    Overall bit rate                         : 599 Kbps
    Writing application                      : Lavf54.36.100
    
    Video
    ID                                       : 1
    Format                                   : AVC
    Format/Info                              : Advanced Video Codec
    Format profile                           : High@L2.1
    Format settings, CABAC                   : Yes
    Format settings, ReFrames                : 4 frames
    Codec ID                                 : avc1
    Codec ID/Info                            : Advanced Video Coding
    Duration                                 : 3h 2mn
    Bit rate                                 : 146 Kbps
    Width                                    : 360 pixels
    Height                                   : 288 pixels
    Display aspect ratio                     : 16:9
    Frame rate mode                          : Constant
    Frame rate                               : 25.000 fps
    Color space                              : YUV
    Chroma subsampling                       : 4:2:0
    Bit depth                                : 8 bits
    Scan type                                : Progressive
    Bits/(Pixel*Frame)                       : 0.056
    Stream size                              : 190 MiB (24%)
    Writing library                          : x264 core 128 r2216 198a7ea
    Encoding settings                        : cabac=1 / ref=2 / deblock=1:0:0 / analyse=0x3:0x113 / me=hex / subme=4 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=0 / me_range=16 / chroma_me=1 / trellis=1 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=0 / threads=3 / lookahead_threads=1 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=1 / b_bias=0 / direct=1 / weightb=1 / open_gop=0 / weightp=1 / keyint=250 / keyint_min=25 / scenecut=40 / intra_refresh=0 / rc_lookahead=20 / rc=crf / mbtree=1 / crf=23.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00
    
    Audio
    ID                                       : 2
    Format                                   : AC-3
    Format/Info                              : Audio Coding 3
    Mode extension                           : CM (complete main)
    Format settings, Endianness              : Big
    Codec ID                                 : ac-3
    Duration                                 : 3h 2mn
    Bit rate mode                            : Constant
    Bit rate                                 : 448 Kbps
    Channel(s)                               : 6 channels
    Channel positions                        : Front: L C R, Side: L R, LFE
    Sampling rate                            : 48.0 KHz
    Bit depth                                : 16 bits
    Compression mode                         : Lossy
    Delay relative to video                  : -1s 24ms
    Stream size                              : 584 MiB (75%)
    30s sample here.
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  10. Member DB83's Avatar
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    Merci.

    The video does indeed look respectable. Not brilliant and you would never get that at that bit-rate.

    You have probably overdone it with the audio and that saved bit-rate could then be applied to the video.
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  11. Yup, I'll experiment with the audio and see how it goes. The reason I left it as is, is that a so-so video + good audio is watchable, while a good video with inaudible audio isn't.
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  12. Member
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    Originally Posted by yetanotherlogin View Post
    Yup, I'll experiment with the audio and see how it goes. The reason I left it as is, is that a so-so video + good audio is watchable, while a good video with inaudible audio isn't.
    Really? 6 channel 448kbps audio for a "conference" ???? but 146kbps video ? It's probably not even real 6-channel discrete audio. Seems a bit of a waste
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  13. I haven't reduced audio before, which is why I simply left "-c:a copy". Should I keep AAC and a lower bit-rate, or use eg. MP3?
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    Originally Posted by yetanotherlogin View Post
    I haven't reduced audio before, which is why I simply left "-c:a copy". Should I keep AAC and a lower bit-rate, or use eg. MP3?

    You 're currently using AC3 , not AAC

    AAC is more efficient type of audio compression than AC3 or MP3.

    I would convert to stereo AAC. For speech, even 64kbps is more than enough, especially if you use AAC v2 (AAC-HE).

    I don't know how to do that stereo conversion with ffmpeg syntax (also ffmpeg's choice of aac encoders are poor, neroaac and apple aac e.g. using qaac are better and consistently rate higher)
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  15. Thanks. BTW, is it possible to only keep some of the channels, so we only hear what's in front of the camcorder and not on the sides?

    "Channel positions : Front: L C R, Side: L R, LFE"
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  16. Member
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    Originally Posted by yetanotherlogin View Post
    Thanks. BTW, is it possible to only keep some of the channels, so we only hear what's in front of the camcorder and not on the sides?

    "Channel positions : Front: L C R, Side: L R, LFE"

    5.1 from a camcorder won't be "real 5.1" - there will be crosstalk betwen channels

    Yes, you can do a custom mix in an audio editor - something like audacity

    "Normal" stereo downmixing filters have a ratio that incorporates all channels (because it's assumed the source 5.1 is real 6 discrete channels, eg. from a DVD or blu-ray with audio done in the studio)
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  17. Thank you. I'll play with Audacity and see how it goes.

    Using this, the 12GB file is compressed down to 450MB. Cool
    Code:
    ffmpeg -i input.mpg -c:v libx264 -vf scale=iw/2:-1 -preset faster -c:a ac3 -ab 192k output.mp4
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