12665 Views 7 Replies Latest reply: Nov 5, 2008 10:46 AM by Jon Walker
I might be wrong but it seems to me that the ".mov" is bigger than the equivalent ".mov" and I wonder what are the differences. Is the "mov" better than "m4v"?
M4V, MP4, and MOV are simply containers. The same compressed H.264/AAC data can be contained in each.
M4V - The M4V file container is used exclusively for H.264/AAC content either protected or unprotected. Limited use of other data tracks can also be found in this container such as "Chapter" or "alternate audio" tracks. This container can also be associated with external graphic data as normally seen in iTunes when "Artwork" is added. By default, this container normally opens in iTunes when double-clicked.
MP4 - The MP4 file is much like the MP4 file container but may additionally hold MPEG4/AAC data as the primary video/audio compression format. It too may contain supplemental data tracks or be associated with external "Artwork" but, by default, opens in the QT player.
MOV - The MOV file container is a generic file container which may contain up to 99 tracks of any valid audio, video, text, "Chapter", "Tween", ""Timecode", "sprite", etc. form of data. It cannot be associated with external "Artwork" but, like M4V and MP4, can have a designated "poster" frame. Any valid file saved using the "Save As..." File option is automatically placed in the MOV file container by default regardless of its original compression format and file container type.
While there are "internal" differences, all three containers have the same basic purpose. It is likely these differences which you see when comparing "file size" even when the actual compressed audio and video data is exactly the same within the container.
ok, but am I wrong or .m4v files are much smaller than equivalent .mov ones?
As I attempted to point out above, it all depends on what you are measuring. The "compressed data" contained in both files is the same. The container, however, may well be larger. It lis like having a cup of milk. It is still a "cup of milk" if it is in a cup or in a quart milk bottle but the quart milk bottle is obviously larger than the cup.
As to the amount of difference in size, this too is difficult to estimate without further information. If you trim a file and use the save command to save the data that remains back to the original container, the container size does not change even if you may have trimmed out most of the data in the file. Also, how are you comparing the files and/or data? Some system routines measure the files/data in terms of base-10 while other routines measure in base-2. (I.e., 1 KB = 1000 bytes or 1KB = 1024 bytes?) In addition, some descriptors describe the file size as data plus container and others in terms of just the data they contain.
Thus, we are back to the statement that the MOV file container is most likely larger (i.e., takes up more hard drive space) than either an MP4 or M4V file container even when all three contain the exact same amount of audio/video data.
what I've done is simply using imovie: first try was to published to mobileme, second try was to convert to mov still from imovie. I then checked the size of the same video either on mobileme (m4v) and on my hard disk (mov) and the last one was larger than the first
Now you are comparing "apples and oranges." The M4V file was created using a specific audio/video combination with specific settings. When you say you "convert to mov" you are not telling us what compression format or settings were used. As stated multiple times above, MOV is a file container. It is not a compression format. You could have converted to DV, AIC, or a H.264/AAC file with an unlimited data rate. In these cases alone, you could end up with an MOV file 15 to 35 times the size of a medium MobileMe file. Since you are comparing different things here, open the file in your QT Player and check the "Inspector" window to compare the total average data rates of your two files. This gives you a direct comparison of the two files no matter what compression format was used for each since the file sizes involved are directly proportional to the total data rates contained in each file. I can, for instance, create files on the order of 280-290 Mbps on my system (at which point my CPUs run out of "horsepower") which means the files would be on the order of 165-170 times larger than a medium MobileMe file. Since you do not seem to know what compression format your MOV file defaulted to when you performed your conversion, it is entirely possible (i.e., even most likely) that there is a huge difference between the sizes of your two files in question here.
from the inspector I see the two movie are both H 264 640x480, the movie generated by iMovie is "Millions AAC" while the other one is 16 Bit Integer, what's the difference?
As far as the video is concerned, H.264 (MPEG-4/AVC) is a highly efficient codec which can be used over an exceptionally wide range of data rates. The iMovie "preset" is targeted at/limited to about 1.5 Mbps. The MOV file on the other hand could be using a different data rate altogether. For instance, in the automatic (i.e., unlimited) setting, it would likely have a data rate on the order of 18.0 ± 2.0 Mbps for a 640x480 containing average brightness, saturation, contrast, and vector motion. Manually limiting the data rate could yield a video data rate anywhere between 0.1 Mbps and about 18.0 Mbps.
As for the audio, AAC is a highly efficient MPEG-4 audio format which would be targeted for most MobileMe movies as stereo audio at 128 Kbps with a sampling rate of 44.1 KHz (or about 67% of what you normally see for 192 Kbps MP3 audio). The MOV audio, on the other hand, sounds like it is Linear PCM (i.e., the kind of audio often used for Commercial CDs) sampled at 48.0 KHz and probably having a data rate of about 1.536 Mbps (or about 12 times the data rate of the AAC audio) usually encoded using 16-bit Integer (Big Endian order). If so, the audio track track alone for the MOV file is probably as large as the Video track of the M4V file.