How to re-encode audio tracks within a multi-language video with FFmpeg?

Question

I have a video with 4 language audio tracks that works nicely within the QuickTime player for 3 of the 4 audio tracks. I think the 4th audio track is encoded differently because the FFmpeg listing showed:

Metadata:
 encoder : Lavc61.3.100 aac

For the 3 audio tracks when the video was made and:

Metadata:
 encoder : LAME3.100

When the additional audio track was added. I've found posts on how to re-encode audio on video with only one audio track, but not on how to re-encode just one audio track in a video containing multiple audio tracks.

I also tried using .m4a and .ac3 audio files instead of .mp3 when making the above videos, but it did not help.

For more details, see a recent post which showed me how to add an additional audio track to a video containing 3 audio tracks. As I explained there, it kinda worked but I was still not able to see the added audio track in the QuickTime player; that's my goal, and I think the above encoding difference is the source of the problem.

Edit: Solved by @Gyan after adding -c:a:3 aac as follows

ffmpeg -i 3.mp4 -i eng.mp3 -i eng.srt -map 0:v -map 0:a -map 1 -map 0:s -map 2 -c copy -c:a:3 aac -c:s:3 mov_text -metadata:s:a:3 language=eng -metadata:s:s:3 language=eng -shortest 3plus1.mp4

media file listing requested by @Gyan

ffmpeg -i 3.mp4 -i eng.mp3 -i eng.srt -map 0:v -map 0:a -map 1 -map 0:s -map 2 -c copy -c:s:3 mov_text -metadata:s:a:3 language=eng -metadata:s:s:3 language=eng -shortest 3plus1.mp4
Output #0, mp4, to '3plus1.mp4':
 Metadata:
 major_brand : isom
 minor_version : 512
 compatible_brands: isomiso2avc1mp41
 encoder : Lavf61.1.100
 Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(progressive), 1280x720 [SAR 1:1 DAR 16:9], q=2-31, 8 kb/s, 25 fps, 25 tbr, 12800 tbn (default)
 Metadata:
 handler_name : VideoHandler
 vendor_id : [0][0][0][0]
 encoder : Lavc61.3.100 libx264
 Stream #0:1(ita): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, mono, fltp, 69 kb/s (default)
 Metadata:
 handler_name : SoundHandler
 vendor_id : [0][0][0][0]
 Stream #0:2(fra): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, mono, fltp, 69 kb/s
 Metadata:
 handler_name : SoundHandler
 vendor_id : [0][0][0][0]
 Stream #0:3(ger): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, mono, fltp, 69 kb/s
 Metadata:
 handler_name : SoundHandler
 vendor_id : [0][0][0][0]
 Stream #0:4(eng): Audio: mp3 (mp4a / 0x6134706D), 48000 Hz, mono, fltp, 75 kb/s
 Metadata:
 encoder : LAME3.100
 Stream #0:5(ita): Subtitle: mov_text (tx3g / 0x67337874), 0 kb/s (default)
 Metadata:
 handler_name : SubtitleHandler
 Stream #0:6(fra): Subtitle: mov_text (tx3g / 0x67337874), 0 kb/s
 Metadata:
 handler_name : SubtitleHandler
 Stream #0:7(ger): Subtitle: mov_text (tx3g / 0x67337874), 0 kb/s
 Metadata:
 handler_name : SubtitleHandler
 Stream #0:8(eng): Subtitle: mov_text (tx3g / 0x67337874)
 Metadata:
 encoder : Lavc61.3.100 mov_text
ffmpeg -f lavfi -i "color=color=black:s=1280x720" \
-i ita.mp3 -i fre.mp3 -i ger.mp3 \
-i ita.srt -i fre.srt -i ger.srt \
-map 0:v -map 1:a:0 -map 2:a:0 -map 3:a:0 \
-map 4:s:0 -map 5:s:0 -map 6:s:0 \
-metadata:s:a:0 language=ita -metadata:s:a:1 language=fra -metadata:s:a:2 language=ger \
-metadata:s:s:0 language=ita -metadata:s:s:1 language=fra -metadata:s:s:2 language=ger \
-c:s:0 mov_text -c:s:1 mov_text -c:s:2 mov_text \
-shortest 3.mp4
Output #0, mp4, to '3.mp4':
 Metadata:
 encoder : Lavf61.1.100
 Stream #0:0: Video: h264 (avc1 / 0x31637661), yuv420p(progressive), 1280x720 [SAR 1:1 DAR 16:9], q=2-31, 25 fps, 12800 tbn
 Metadata:
 encoder : Lavc61.3.100 libx264
 Side data:
 cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: N/A
 Stream #0:1(ita): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, mono, fltp, 69 kb/s (default)
 Metadata:
 encoder : Lavc61.3.100 aac
 Stream #0:2(fra): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, mono, fltp, 69 kb/s
 Metadata:
 encoder : Lavc61.3.100 aac
 Stream #0:3(ger): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, mono, fltp, 69 kb/s
 Metadata:
 encoder : Lavc61.3.100 aac
 Stream #0:4(ita): Subtitle: mov_text (tx3g / 0x67337874) (default)
 Metadata:
 encoder : Lavc61.3.100 mov_text
 Stream #0:5(fra): Subtitle: mov_text (tx3g / 0x67337874)
 Metadata:
 encoder : Lavc61.3.100 mov_text
 Stream #0:6(ger): Subtitle: mov_text (tx3g / 0x67337874)
 Metadata:
 encoder : Lavc61.3.100 mov_text

• Alain1A45: Try : ffmpeg -i 3.mp4 -i eng.mp3 -i eng.srt -map 0:v -map 0:a -map 1 -map 0:s -map 2 -c copy -c:a:3 libmp3lame -c:s:3 mov_text -metadata:s:a:3 language=eng -metadata:s:s:3 language=eng -shortest 3plus1.mp4
• Tony M: @Alain1A45 the result is the same: the additional (english) audio does not appear in the QT player. However, I notice that the encoder that is listed by ffmpeg is different now. It now shows as "encoder : Lavc61.3.100 libmp3lame" -- I also tried using .m4a and .ac3 when making both 3.mp4 and 3plus1.mp4 -- nothing seems to work. From what I've read the QT player is very difficult for things like this -- thanks again.
• Alain1A45: If you want, you can also try to put the English tracks first in the output file : ffmpeg -i 3.mp4 -i eng.mp3 -i eng.srt -map 0:v -map 1 -map 0:a -map 2 -map 0:s -c copy -c:s:0 mov_text -metadata:s:a:0 language=eng -metadata:s:s:0 language=eng -shortest 3plus1.mp4
• Tony M: that didn't work either -- but at least through all these examples I'm understanding ffmpeg a little more...
• Gyan: 3plus1.mp4 shows the reverse: the first 3 tracks are aac whereas the new one is mp3. Add -c:a:3 aac when generating 3plus1 and check.