About codecs, bit rates, sampling rates and so on
Mar 28, 2013 10:45:00 GMT -5
Post by Deleted on Mar 28, 2013 10:45:00 GMT -5
A lady has written in from Liverpool, inquiring. Since at least one Member has requested the opportunity to consider the question here, I reproduce my response:
The sound track - which is the important part - uses in the first three broadcasts aacPlus v2 encoding, also known as eAAC+, also known as HE-AAC v2. Such audio files are often given the extension m4a. The sample rate is 44100 Hertz and the average bit rate used - after some experimentation - is 256 kilobits per second. Bear in mind that the original sound sources for the programmes - so far - have been quite low in quality; our aim has been simply to ensure that nothing we do reduces the quality further.
The video track is standard H264, resolution 720 by 480 pixels, and a frame rate of 25 per second.
Any of these audio and video parameters may be changed if required for future broadcasts. For example, the sharp and clear display of a full page of orchestral score requires at the very least a height of 768 pixels (although something over 1000 would be preferable); that will be just manageable on a lap-top. We are experimenting with files having more than one video track - one for each of two or three different resolutions, and (in the case of Liszt's Faust Symphony, say, or Dr. Williams's Sea Symphony) one video track for the poetry, another for the full score, and a third for a real-time analysis, allowing the listener to switch between the various video tracks at will while the music is playing.
I have tested the broadcasts with four different media players: VLC, MPlayer, WinAmp, and the Windows Media Player; no problems have arisen.
The Internet Archive Video department is very good, because it permits listeners to download a file that is indentical with the file originally uploaded by the creator - and without commercial pressure or advertisements.
The sound track - which is the important part - uses in the first three broadcasts aacPlus v2 encoding, also known as eAAC+, also known as HE-AAC v2. Such audio files are often given the extension m4a. The sample rate is 44100 Hertz and the average bit rate used - after some experimentation - is 256 kilobits per second. Bear in mind that the original sound sources for the programmes - so far - have been quite low in quality; our aim has been simply to ensure that nothing we do reduces the quality further.
The video track is standard H264, resolution 720 by 480 pixels, and a frame rate of 25 per second.
Any of these audio and video parameters may be changed if required for future broadcasts. For example, the sharp and clear display of a full page of orchestral score requires at the very least a height of 768 pixels (although something over 1000 would be preferable); that will be just manageable on a lap-top. We are experimenting with files having more than one video track - one for each of two or three different resolutions, and (in the case of Liszt's Faust Symphony, say, or Dr. Williams's Sea Symphony) one video track for the poetry, another for the full score, and a third for a real-time analysis, allowing the listener to switch between the various video tracks at will while the music is playing.
I have tested the broadcasts with four different media players: VLC, MPlayer, WinAmp, and the Windows Media Player; no problems have arisen.
The Internet Archive Video department is very good, because it permits listeners to download a file that is indentical with the file originally uploaded by the creator - and without commercial pressure or advertisements.
