Thursday, September 14, 2006

iPod H.264 video quality test

QuickTime 7.1.3 brings us new 640x480 H.264 video files that are compatible with the latest iPods (and the last generation iPods after the 1.2 software update).

However, as suspected, the 1.5 Mbps video bitrate limitation (along with the encoder settings) can be problematic with some content.

To illustrate this, I have taken this Cornell Laboratory of Ornithology HD video and re-encoded it to 320x180 (0.8 Mbps, 11.5 MB) using QuickTime 7.1.2 and 640x360 (1.6 Mbps, 23.1 MB) using QuickTime 7.1.3, with their respective default "Export Movie to iPod" settings.

Although the re-encoded 640x360 video looks fairly good in most areas, unfortunately in some spots the results are not pretty.

Here is a screengrab of the original high definition video, scaled down to 640x360 in QuickTime Player:

Here is the HD video re-encoded to 640x360 using QuickTime 7.1.3's "Export Movie to iPod" function:

Here is the HD video re-encoded to 320x180 using QuickTime 7.1.2's "Export Movie to iPod" function, and scaled up to 640x360 in QuickTime Player:

While there is (not surprisingly) a noticeable improvement going from 320x180 to 640x360 when viewing video at larger screen sizes, a higher bitrate (or different settings) for the latter would have been preferred. Unfortunately, it's likely that hardware limitations of the iPod prevent use of higher bitrate H.264, since it may be too difficult for the iPod's CPU to decode cleanly. (This is in contrast to last year's 320x240 H.264 limitation, which seems now to have been an intentional software limitation.) Overall though, the video looks pretty reasonable, and will satisfy most users, even with TV playback from the iPod.

[Update 2006-09-14]

It appears that several third party video encoders do not support the Baseline Low Complexity Profile required by the iPod for 640x480 H.264 video. For example, video encoded at that resolution directly from DVD using the popular Handbrake application does not work on the iPod. MPEG4 video continues to work fine, however.


Anonymous said...

I think this is because it was compressed twice. If the original was compressed to the latest quicktime this probably would not have happened.

Eug said...

I compressed the original HD file to iPod 640x360 using QuickTime 7.1.3 directly.

Furthermore, one can change the settings/bitrate to improve the quality. However, the tweaked exports will not be compatible with the iPod.

Anonymous said...

Telling the truth I did encoded many DVDs for my 5G iPod with handbrake.
You have to select the baseline profile and then to restrict the bitrate to 700.
Resize to a max of 320x240 and you're done.
quite an easy task I'd say, probably you had set too high bitrates.

Eug said...

It's for playback on a TV, so I don't want 320x240 video.

Baseline profile doesn't work for 640x480 iPod H.264 video. It must be baseline low complexity profile, which is not supported by Handbrake.

Anonymous said...

It seems that someone has developed a version of Handbrake that will do just this... At least for PPC.

Great article, BTH!

Eug said...


iPod Guy said...

The converter I'm using: PQ DVD to iPod Video Suite, also have the supports of 640x480 H.264 and MPEG4.

xvid to ipod said...

I found those pictures very amazing. iPod is just an amazing gadget that we must have. That is just one proof that it is the best thing today.