Watching movies on your phone

I'm now keeping a live journal, when I'm not administering my new site, for60secs.

I recently got a new phone - a Nokia 3650 - that can play video. The format is 3gp, a flavor of QuickTime. Nokia makes a Windows-based encoding tool, but I wanted to use ffmpeg. Using the latest (December 2003) CVS snapshot of ffmpeg it's possible to encode directly to 3gp using free software.

(My goal here was to be able to watch entire movies on my cellphone. I watch a lot of movies on DVD, and very often want to listen to the director's commentary tracks. Instead of sitting through the movie at home a second time, I can hear (and watch) the commentary next day on my phone.)

Audio quality? Like listening to a movie through a phone call, unsurprisingly.
What about video quality? 30kbps is just about good enough to tell what's going on. Resolution is 176x144, but there's severe blockiness when there's a lot of motion. A frame rate of 12fps seems to give good results.
aDoes playing video drain the battery? Yes, but you can watch over 3 hours on a single charge.
How much video can the phone store? Depends how much you compress it, but with reasonable settings 1 megabyte holds 3 minutes of video. So the standard 16MB MMC card in the phone can hold at most 48 minutes of video. And a 128MB MMC card can hold 384 minutes, or 2-4 complete movies.
Can you rewind and fast-forward? Yes, the 3650 documentation doesn't mention it, but pressing up and down from RealPlayer lets you move around the video.
What software do you use? mencoder and the latest ffmpeg, both run on Linux and FreeBSD.
How long does conversion take? A 100 minute movie takes about an hour on a 1GHz Pentium III.
How does it look? Well, here is a compilation of 70's telephone ads (what else?) courtesy of archive.org that I encoded using mplayer and ffmpeg.

How?

Get the latest version of ffmpeg, look at ffmpeg/libavcodec/amr.c and follow the instructions in this file to enable amr/3gp support.

To convert the first 60 seconds of an AVI file:

./ffmpeg -i foo.avi
-s qcif -r 12          # convert video to 176x144 at 12 fps
-ac 1 -ar 8000         # convert audio to mono, 8000 Hz
-b 30                  # video rate 30kbps
-ab 12                 # audio rate 12kbps
-t 60                  # first 60 seconds only
foo.3gp                # output file

Choosing bitrates

There are some useful encoding guidelines here:

http://docs.real.com/docs/mobile/encoding_recommendations.pdf

I settled on 12fps QCIF, 30kbps video, 12kbps audio. At this rate, 30 minutes of movie takes 10 Mbytes.

Improvements

One problem is that the sound level is often too low in the source material. Another is that ffmpeg stretches the picture to fit the frame, which is fine for regular video but not right for anamorphic DVDs. Both these issues can be fixed by first using mencoder to extract video and audio streams, filtering these, then merging them back with ffmpeg.

Here's how:

Extract video with mencoder. Scale to 176 wide, then center in a 176x144 frame.

mencoder movie.vob \
-nosound \
-ovc lavc -lavcopts vcodec=mpeg4 \
-vop expand=176:144,scale=176:-2 -o movie.avi -ofps 12

Extract audio with mplayer. Resample to 8000Hz, turn up the volume with a soft clip filter.

mplayer -vo null -ao pcm -af resample=8000,volume=+16db:sc movie.vob
mv audiodump.wav movie.wav

Combine audio and video with ffmpeg. Give ffmpeg the two input streams, then use the -map option to tell it which to read video and audio from.
```
ffmpeg -i movie.avi
-i movie.wav \
-b 30 \
-ac 1 -ab 12 \
-map 0.0 -map 1.0 \
movie.3gp
```

Transfer

Bluetooth is the obvious way to transfer files from a PC to the phone, and the video will appear as a Bluetooth message when the transfer is done. By default the phone stores messages in main memory, so there's a 4MB size limit. By changing the messaging options, however, you can get messages to go straight into the MMC, raising this limit to 16MB. I get about 1.2 megabytes/minute over Bluetooth.

A faster way is to remove the MMC card from the phone and put it in an MMC reader/writer. These cost under $20. But it isn't clear that the phone's battery and MMC sockets are designed for a large number of insertions.