[theora-dev] Using Theora Micro-HOWTO

[Dan Miller]

cool.  I'm just up to the "autogen doesn't work" stage, so this should help alot.
 
I'd be curious if anyone gets this to work in cygwin -- I'm sticking with Redhat 7.2 to start, since I know I've got most of what I need compiled there.

        -----Original Message----- 
        From: emaillist at dogphilosophy.net [mailto:emaillist at dogphilosophy.net] 
        Sent: Fri 9/27/2002 2:25 PM 
        To: theora-dev at xiph.org 
        Cc: 
        Subject: [theora-dev] Using Theora Micro-HOWTO
        
        

        Okay, thanks to some stubbornness on my part and helpfulness on the part
        of people on this mailing list, I got the Ogg Theora alpha compiled up
        and installed and running.
        
        Yesterday, I went to the Prelinger archives (the public-domain video
        archive at www.archive.com) to find a high-quality original to re-encode
        as a test.  The encoder worked just fine, and playback as well, and I thought
        I'd share what I found with the thought that it might help others.
        
        COMPILING:
        
        Both the encoder and the player rely on STATIC versions of their respective
        libraries.  I believe both the ogg and vorbis libraries build static versions
        as well as shared when compiled, but some (e.g. libartsc) don't.  (Most
        pre-compiled packages probably include static versions, however.)
        
        Otherwise, simply running the supplied ./autogen.sh script followed by 'make'
        should build the code just fine.  'make install' places the theora library
        (by default) in /usr/local/lib, but does not copy the example player or
        encoder.  If you want them moved out of the examples directory in the source
        tree, you'll have to do it by hand (you may or may not want to bother,
        considering that both are A)merely examples and B)still in early 'alpha'
        testing, though in my limited experience thus far they both seem to perform
        reasonably well.)
        
        ENCODING:
        
        The encoder, as the README states, expects raw, uncompressed 'yuv4mpeg'
        data for video, and '.wav' files (pcm) for sound.  As the readme also
        explains, mplayer ( http://www.mplayerhq.hu ) is an easy way to export
        from an existing video file to this format.
        
        It's not explicitly stated in the README, but the example encoder's output
        is to stdin, so the output needs to be redirected in the command line to the
        appropriate filename (or, if desired, piped directly to another program for
        output.)
        
        For those who don't have a 300GB hard drive to a raw, uncompressed file
        on, you can actually pipe yuv4mpeg data 'on-the-fly' from mplayer to
        the example encoder by creating a fifo "pipe" file:
        
        mkfifo -m 660 stream.yuv
        
        the example encoder, as of this writing, does not yet also handle the audio
        from a fifo, though this may be possible in the (near?) future.  In the
        meantime, the simplest workaround is to dump the audio, separately, to a
        standard .wav file (which can be rather large, but still MUCH smaller than
        the video dump file would be...):
        
        mplayer -ao pcm -aofile stream.wav -vo null file_to_be_encoded.avi
        
        Finally, to encode the Ogg Theora file from the original:
        
        mplayer -ao null -nosound -vo yuv4mpeg file_to_be_encoded.avi &
        
        (and then - I do this in a separate terminal window, but as far as I know
        it can be done in the same window, albeit messily as both programs output
        status messages)
        
        encoder_example -v 1 -a 1 stream.wav stream.yuv > theora_file.ogg
        
        (if/when encoder_example supports 'piped' pcm data, you will be able to:
        
        mkfifo -m 660 stream.wav
        
        and there will be only one mplayer command line to call before the
        encoder_example:
        
        mplayer -ao pcm -aofile stream.wav -vo yuv4mpeg file_to_be_encoded.avi &
        
        The encoder_example line above can remain unchanged, unless you want to
        modify the quality settings or supply target bitrates instead.
        
        
        On final encoding note:  The encoder takes the size and frame rate of the
        output video directly from the yuv4mpeg stream, and does not yet handle
        'aspect ratio' (either that, or the player_example doesn't), so if you
        want to, for example, create an ogg-theora file from an NTSC SVCD mpeg file
        (480x480) that displays the "correct" size (640x480), you will need to
        explicitly scale it.  Fortunately, mplayer handles this just fine:
        
        mplayer -ao null -nosound -vo yuv4mpeg -vop scale=640:480 SVCD_File.mpg
        
        Some 'data points':
        -a 1, for 44.1khz stereo .wav file, equates to ~64-72kbps
        -v 1, for 640x480 29.970fps video, equates to ~600kbps
        
        I've tested 'transcoding' a 13-minute-long, 368x480, 29.970 fps, 3750.0 kbps
        color mpeg2 video, 112kbps (?) audio file (Total file size ~315MB)from the
        Prelinger archives as described above, scaling to 640x480, with no problems.
        Synchronization seems fine throughout, and even at -v 1, the resulting video
        did not seem noticeably degraded from the original, though in fairness, the
        original in this case is a faded and grainy 1950's film, so what degradation
        there was is likely to be less noticeable.
        7
        The resulting Theora file was ~68MB.
        
        PLAYBACK:
        
        Playback by the player_example, as also explicitly stated in the README,
        takes its input from stdin.  However, since *I* read that and STILL tried
        to supply a filename the first time or two that I ran it, I'll reiterate it
        here to cover up my stupidity:
        
        player_example expects data on stdin, that is, piped.  To play back an Ogg
        Theora file with it, use a command line such as:
        
        cat Ogg_Theora_File.ogg | player_example
        
        or simply:
        
        player_example < Ogg_Theora_File.ogg
        
        The example player has no options or playing controls, but plays
        back just fine in my experience so far.
        
        TODO:
        
        Test encoding with some 'sharper' originals.
        
        Compare encoding speed and quality with mpeg2 and xvid.
        
        
        
        
        
        Comments?  Questions?  Suggestions?
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