Update track selection logic for missing IDs

[damontecres]

Description

This is a major rewrite of the audio/subtitle track selection logic.

Instead of trying to match the server's index to a track's ID, the implementation now calculates the desired index's offset and uses that to select a track.

This means there is the assumption that that the indexes for each MediaStream in the MediaSourceInfo will be ordered as:

1. External subtitles
2. Video streams
3. Audio streams
4. Embedded subtitles

Note: this assumption is not new, the previous code assumed this as well, but wasn't as upfront about it.

Thus for a file with 1 external subtitle, 1 video, 2 audio, & 3 embedded subtitles and you want the second audo track (index=3):

1. Count everything before the first audio (2)
2. Subtract that from the desired index: 3-2=1
3. Find the 1 indexed audio track in the actual file, ie the second audio track

Related issues

Maybes fixes #791

Testing

Existing unit tests pass. Added additional test cases for a missing ID

I also crafted an mp4 and rewrote the track IDs so there was a gap in the IDs (none with ID=2). Before this PR, Wholphin was unable to switch audio tracks (the official app failed as well). With these change, it can.

I was unable to craft a similar mkv that played successfully and I believe this is because the mkv spec doesn't allow for missing IDs. This is why I'm unsure if #791 is fully resolved by this PR since the OP's issue occurs with a mkv.

Media info

Format                                   : MPEG-4
Format profile                           : Base Media
Codec ID                                 : isom (isom/iso2/avc1/mp41)
File size                                : 1 013 MiB
Duration                                 : 1 h 6 min
Overall bit rate                         : 2 134 kb/s
Frame rate                               : 29.970 FPS
Writing application                      : Lavf62.3.100

Video
ID                                       : 1
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : High@L3
Format settings                          : CABAC / 4 Ref Frames
Format settings, CABAC                   : Yes
Format settings, Reference frames        : 4 frames
Codec ID                                 : avc1
Codec ID/Info                            : Advanced Video Coding
Duration                                 : 1 h 6 min
Bit rate                                 : 1 656 kb/s
Width                                    : 720 pixels
Height                                   : 480 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Variable
Frame rate                               : 29.970 FPS
Minimum frame rate                       : 18.182 FPS
Maximum frame rate                       : 83.333 FPS
Standard                                 : NTSC
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Bits/(Pixel*Frame)                       : 0.160
Stream size                              : 786 MiB (78%)
Writing library                          : x264 core 148
Encoding settings                        : cabac=1 / ref=2 / deblock=1:0:0 / analyse=0x3:0x113 / me=hex / subme=6 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=1 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-2 / threads=12 / lookahead_threads=2 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=1 / b_bias=0 / direct=1 / weightb=1 / open_gop=0 / weightp=1 / keyint=250 / keyint_min=25 / scenecut=40 / intra_refresh=0 / rc_lookahead=30 / rc=crf / mbtree=1 / crf=1.0 / qcomp=0.60 / qpmin=0 / qpmax=34 / qpstep=4 / vbv_maxrate=1666 / vbv_bufsize=3332 / crf_max=25.0 / nal_hrd=none / filler=0 / ip_ratio=1.40 / aq=1:1.00
Language                                 : English
Tagged date                              : 2026-02-07 20:08:08 UTC
Menus                                    : 5
mdhd_Duration                            : 3981065
Codec configuration box                  : avcC

Audio #1
ID                                       : 3
Format                                   : AAC LC
Format/Info                              : Advanced Audio Codec Low Complexity
Codec ID                                 : mp4a-40-2
Duration                                 : 1 h 6 min
Bit rate mode                            : Constant
Bit rate                                 : 341 kb/s
Channel(s)                               : 6 channels
Channel layout                           : C L R Ls Rs LFE
Sampling rate                            : 48.0 kHz
Frame rate                               : 46.875 FPS (1024 SPF)
Compression mode                         : Lossy
Stream size                              : 162 MiB (16%)
Title                                    : Surround 5.1
Language                                 : English
Default                                  : Yes
Alternate group                          : 1
Tagged date                              : 2026-02-07 20:08:08 UTC
Menus                                    : 5

Audio #2
ID                                       : 4
Format                                   : AAC LC
Format/Info                              : Advanced Audio Codec Low Complexity
Codec ID                                 : mp4a-40-2
Duration                                 : 1 h 6 min
Bit rate mode                            : Constant
Bit rate                                 : 132 kb/s
Channel(s)                               : 2 channels
Channel layout                           : L R
Sampling rate                            : 48.0 kHz
Frame rate                               : 46.875 FPS (1024 SPF)
Compression mode                         : Lossy
Stream size                              : 61.7 MiB (6%)
Title                                    : Stereo
Language                                 : Spanish
Default                                  : No
Alternate group                          : 1
Tagged date                              : 2026-02-07 20:08:08 UTC
Menus                                    : 5

Screenshots

N/A

AI or LLM usage

None

[DrHurt]

Looking forward to testing this. Hope it makes it into next build.