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Can you play music straight from an Android microSD card?

If you have say a Samsung Galaxy S4 and a 64GB microSD card, can you fill the card with music? And would class be important?

Most Useful Answer mpenrice  Oct. 29, 2013 at 14:18

1/ Yes, you can fill the card with music. Quite a lot of it, in fact, so long as you don't fancy taking any photos/recording videos/downloading apps etc. I'd personally suggest reserving no more than 1/4 to 1/3rd of the card for music. That'll still give you storage space equivalent to a 16gb dedicated player or an old 20gb HDD based one, but with a better range of higher-efficiency codecs to store it with. For example, AAC-HE at 128kbit will sound basically CD-transparent (you can generally expect 1.5 to 2x the efficiency of MP3), and within that space you can store 270 to 360 hours of music (11 to 15 solid days' worth). I've got a little under 1Gb of lower-rate AACs on my rather smaller card, and 40ish hours at 56kbit rate is still perfectly good for casual listening (this old phone still isn't my main music player).

2/ Yes, of course you can play it straight off the card. This is 2013, not 2003, and we're not using hilariously and inexplicably crippled Apple hardware. You can even run your apps directly off the card.

3/ Class is always important. Though, actually, when it comes to mSD cards and digital music, not so much. Compressed audio formats were designed so you could stream music over very low-speed data links - modems, digital radio channels, the small chunk of bandwidth allocated for sound on a Video CD, etc. Even the smallest, slowest SD card is several times quicker than the highest supported MP3 encoding rate, let alone AAC. My 56k ones should, at least theoretically, be suitable for streaming down a phone line (and the 48k ones, definitely so), and even a pretty rotten-by-modern-standards serial link could handle up to 112k.

The slowest registered "class" of mSD card, especially up at the 64GB level, will be Class 2, equal to a sustained R/W rate of 2Mbyte/sec, and you're unlikely to see anything less than Class 4 for big cards. The latter is equivalent to about 32,000 kbits - or 100x maximum MP3 rate. In other words, with a suitably quick link between the card and a host machine (USB2 easily covers it), you could copy an hour's worth of music one way or the other in 36 seconds at the highest typically used quality* ... and more like 20 seconds for yer usual medium-rate VBRs, or 15 seconds for AAC-HEs (and yet, it will still take 4 1/2 hours to completely fill or empty a 64GB card at Class 4 speed). Thus any standard class of modern SD card will be easily fast enough for audio playback.

In fact, that's fast enough to support completely uncompressed playback of full-on surround sound; you might be able to drag 7.1 DTS at 192kHz/24 bit out of it with a bit of luck, which is just stupidly high-fidelity. Certainly, 5.1 at 96kHz and 20 bit would be easily achievable.

Class is much more important for live video recording and high-quality photography (especially with RAW files), and is the main reason it was dreamt up to replace the old "X" system which referred to CDROM transfer speed (1x = 150kbyte/sec, or 1200 kbit... thus USB 1 is about 10x, and a typical memory card may be anywhere from about 6x at the low end (900kbyte/sec, which would seem sluggish in all but the naffest digital cameras) through to very high end ones at 150x or so (22.5Mybte/sec)), and wasn't ever clear about whether it referred to write speed (quite hard to achieve good rates with flash memory), or just read speed (much easier to achieve, as well as rather less critical), with only professional cards ever offering, say, "66x R/W" (roughly equivalent to modern Class 10).

If you have a Class 6 card, then you know you can rely on it to accept and safely store a data stream presented to it at 6Mbyte/sec or less, regardless of anything else going on. Or in other words, 48Mbits.

HD video seems to be recorded at certain standard rates (no reason for it, but it seems there's a bunch of unofficial standards shared by manufacturers) - 13, 17, 21 and I think 24 and 27Mbit/s are ones I've seen, but there's still options on going higher. A "class 2" card could only be assured of being suitable for 13Mbit HD (most likely 720p, possibly even only at 25/30fps not 50/60) or lower rate SD material. For 17 thru 24 you'd need a notional "class 3" card (which don't, AFAIK, actually exist), and to record 27Mbit material (full 1080i or even 1080p maybe) you need a Class 4 card (27Mbit = approx 3.4 Mbyte/s).

So even for video recording, Class 4 is generally enough, unless you're maxing it and going for the highest that even Blu-Ray supports, at 54Mbit (which would need a Class 8 card). The highest speeds are actually most useful to photographers in the live setting (if you're shooting at 12 megapixels, in 16bpp RAW mode, that's 24MB of data per frame; even though pro cameras have RAM buffers to allow rapid shooting, there's only so much they can store at once, and having an (unofficial) Class 20 card vs a Class 8 or Class 2 means each of those shots only taking a maximum of 1.2 seconds to transfer instead of 3 seconds... or 12. The extra speed is also handy for copying off your recorded video at a higher speed than you recorded it; e.g. you should be able to copy a 24Mbit video off a Class 6 card at no less than 2x real-time speed, and hopefully quite a bit more - and if you've splashed out for a Class 20, then that becomes 6.6x or better.

The higher speed ones will eventually come into their own when people start to want to record 4K (and then 8K) video, mind. Generally you should assume a 4-fold increase in data rate for each of those steps up from 1080p; if, say, we assume 27mbit is the max for 1080i and 54mbit for 1080p, then these could potentially demand up to 216 and then 864Mbit record rates - or 27 and 108Mbyte/sec! Thus we'll need super-high end Class 30 and Class 120 cards for those... don't even know if they exist yet!

(Are you not educated, now? :))

tl;dr version
Yes you can do this, and no you shouldn't be bothered unless you're planning to take lots of high-rez RAW photos or shoot a lot of high-rate HD video. Basically any 64GB card that's tested compatible with your phone will be just fine.
However, if you want to avoid having to sit around for absolute donkey's years whilst the data actually copies, I'd recommend buying at least a Class 8 if not a Class 10, as they could improve the copy speed by a good 2 to 2 1/2 times over a regular Class 4 (saving at least 2 hours off a full-card backup), and shouldn't cost massively more.

((In case you were wondering, USB2 should support up to the equivalent of about Class 24 without much difficulty, and maybe Class 30 if you've got a good chipset; however, most Class 8 cards should easily saturate that link when *reading* even if their write speed is only a third of it, so a blazing fast Class 16/20/24 card is unlikely to be worth the much greater cost given that any bulk uploads will be fairly rare occurrences vs bulk download backups))

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3 comments

JanSt / MOD  Oct. 29, 2013 at 13:38

Of course you can play music straight from an SD card. It's what they're there for.
Class determines, basically, the read/write speed. So the higher the class the faster the machine can deal with what's on the card... For something like listening to music you won't notice life altering differences. But: if you have game data on a card, or 4000 photos and 2000 songs, you will notice less or more lag/delay when opening the gallery or the music app.
All those files need to be indexed. Photo thumbnails need to get generated etc etc....
As a simplified rule: If you NEED a 64GB card because YOU NEED the space for loadsa stuff, then you need all the stuff and you want it fast. So: Buy a fast card.

mpenrice  Oct. 29, 2013 at 14:18

1/ Yes, you can fill the card with music. Quite a lot of it, in fact, so long as you don't fancy taking any photos/recording videos/downloading apps etc. I'd personally suggest reserving no more than 1/4 to 1/3rd of the card for music. That'll still give you storage space equivalent to a 16gb dedicated player or an old 20gb HDD based one, but with a better range of higher-efficiency codecs to store it with. For example, AAC-HE at 128kbit will sound basically CD-transparent (you can generally expect 1.5 to 2x the efficiency of MP3), and within that space you can store 270 to 360 hours of music (11 to 15 solid days' worth). I've got a little under 1Gb of lower-rate AACs on my rather smaller card, and 40ish hours at 56kbit rate is still perfectly good for casual listening (this old phone still isn't my main music player).

2/ Yes, of course you can play it straight off the card. This is 2013, not 2003, and we're not using hilariously and inexplicably crippled Apple hardware. You can even run your apps directly off the card.

3/ Class is always important. Though, actually, when it comes to mSD cards and digital music, not so much. Compressed audio formats were designed so you could stream music over very low-speed data links - modems, digital radio channels, the small chunk of bandwidth allocated for sound on a Video CD, etc. Even the smallest, slowest SD card is several times quicker than the highest supported MP3 encoding rate, let alone AAC. My 56k ones should, at least theoretically, be suitable for streaming down a phone line (and the 48k ones, definitely so), and even a pretty rotten-by-modern-standards serial link could handle up to 112k.

The slowest registered "class" of mSD card, especially up at the 64GB level, will be Class 2, equal to a sustained R/W rate of 2Mbyte/sec, and you're unlikely to see anything less than Class 4 for big cards. The latter is equivalent to about 32,000 kbits - or 100x maximum MP3 rate. In other words, with a suitably quick link between the card and a host machine (USB2 easily covers it), you could copy an hour's worth of music one way or the other in 36 seconds at the highest typically used quality* ... and more like 20 seconds for yer usual medium-rate VBRs, or 15 seconds for AAC-HEs (and yet, it will still take 4 1/2 hours to completely fill or empty a 64GB card at Class 4 speed). Thus any standard class of modern SD card will be easily fast enough for audio playback.

In fact, that's fast enough to support completely uncompressed playback of full-on surround sound; you might be able to drag 7.1 DTS at 192kHz/24 bit out of it with a bit of luck, which is just stupidly high-fidelity. Certainly, 5.1 at 96kHz and 20 bit would be easily achievable.

Class is much more important for live video recording and high-quality photography (especially with RAW files), and is the main reason it was dreamt up to replace the old "X" system which referred to CDROM transfer speed (1x = 150kbyte/sec, or 1200 kbit... thus USB 1 is about 10x, and a typical memory card may be anywhere from about 6x at the low end (900kbyte/sec, which would seem sluggish in all but the naffest digital cameras) through to very high end ones at 150x or so (22.5Mybte/sec)), and wasn't ever clear about whether it referred to write speed (quite hard to achieve good rates with flash memory), or just read speed (much easier to achieve, as well as rather less critical), with only professional cards ever offering, say, "66x R/W" (roughly equivalent to modern Class 10).

If you have a Class 6 card, then you know you can rely on it to accept and safely store a data stream presented to it at 6Mbyte/sec or less, regardless of anything else going on. Or in other words, 48Mbits.

HD video seems to be recorded at certain standard rates (no reason for it, but it seems there's a bunch of unofficial standards shared by manufacturers) - 13, 17, 21 and I think 24 and 27Mbit/s are ones I've seen, but there's still options on going higher. A "class 2" card could only be assured of being suitable for 13Mbit HD (most likely 720p, possibly even only at 25/30fps not 50/60) or lower rate SD material. For 17 thru 24 you'd need a notional "class 3" card (which don't, AFAIK, actually exist), and to record 27Mbit material (full 1080i or even 1080p maybe) you need a Class 4 card (27Mbit = approx 3.4 Mbyte/s).

So even for video recording, Class 4 is generally enough, unless you're maxing it and going for the highest that even Blu-Ray supports, at 54Mbit (which would need a Class 8 card). The highest speeds are actually most useful to photographers in the live setting (if you're shooting at 12 megapixels, in 16bpp RAW mode, that's 24MB of data per frame; even though pro cameras have RAM buffers to allow rapid shooting, there's only so much they can store at once, and having an (unofficial) Class 20 card vs a Class 8 or Class 2 means each of those shots only taking a maximum of 1.2 seconds to transfer instead of 3 seconds... or 12. The extra speed is also handy for copying off your recorded video at a higher speed than you recorded it; e.g. you should be able to copy a 24Mbit video off a Class 6 card at no less than 2x real-time speed, and hopefully quite a bit more - and if you've splashed out for a Class 20, then that becomes 6.6x or better.

The higher speed ones will eventually come into their own when people start to want to record 4K (and then 8K) video, mind. Generally you should assume a 4-fold increase in data rate for each of those steps up from 1080p; if, say, we assume 27mbit is the max for 1080i and 54mbit for 1080p, then these could potentially demand up to 216 and then 864Mbit record rates - or 27 and 108Mbyte/sec! Thus we'll need super-high end Class 30 and Class 120 cards for those... don't even know if they exist yet!

(Are you not educated, now? :))

tl;dr version
Yes you can do this, and no you shouldn't be bothered unless you're planning to take lots of high-rez RAW photos or shoot a lot of high-rate HD video. Basically any 64GB card that's tested compatible with your phone will be just fine.
However, if you want to avoid having to sit around for absolute donkey's years whilst the data actually copies, I'd recommend buying at least a Class 8 if not a Class 10, as they could improve the copy speed by a good 2 to 2 1/2 times over a regular Class 4 (saving at least 2 hours off a full-card backup), and shouldn't cost massively more.

((In case you were wondering, USB2 should support up to the equivalent of about Class 24 without much difficulty, and maybe Class 30 if you've got a good chipset; however, most Class 8 cards should easily saturate that link when *reading* even if their write speed is only a third of it, so a blazing fast Class 16/20/24 card is unlikely to be worth the much greater cost given that any bulk uploads will be fairly rare occurrences vs bulk download backups))

JanSt / MOD  Oct. 29, 2013 at 15:25

That was thorough.
Thanks :)

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