On Wed, Jan 6, 2016 at 1:25 PM, Michael Niedermayer
<mich...@niedermayer.cc> wrote:
> On Tue, Jan 05, 2016 at 09:51:15PM -0800, Ganesh Ajjanagadde wrote:
>> On Tue, Jan 5, 2016 at 4:57 PM, Michael Niedermayer
>> <mich...@niedermayer.cc> wrote:
>> > On Tue, Jan 05, 2016 at 01:57:09PM -0800, Ganesh Ajjanagadde wrote:
>> >> On Tue, Jan 5, 2016 at 11:01 AM, wm4 <nfx...@googlemail.com> wrote:
>> >> > On Tue, 5 Jan 2016 08:32:02 -0800
>> >> > Ganesh Ajjanagadde <gajja...@mit.edu> wrote:
>> >> >
>> >> >> On Tue, Jan 5, 2016 at 5:29 AM, wm4 <nfx...@googlemail.com> wrote:
>> >> >> > On Mon, 4 Jan 2016 17:50:01 -0800
>> >> >> > Ganesh Ajjanagadde <gajjanaga...@gmail.com> wrote:
>> >> >> >
>> >> >> >> ffio_ensure_seekback can fail due to e.g ENOMEM. This return value
>> >> >> >> is
>> >> >> >> checked here and a diagnostic is logged.
>> >> >> >>
>> >> >> >> All usage of ffio_ensure_seekback in the codebase now has the
>> >> >> >> return value checked.
>> >> >> >>
>> >> >> >> Reviewed-by: wm4 <nfx...@googlemail.com>
>> >> >> >> Reviewed-by: Ronald S. Bultje <rsbul...@gmail.com>
>> >> >> >> Reviewed-by: Michael Niedermayer <mich...@niedermayer.cc>
>> >> >> >> Signed-off-by: Ganesh Ajjanagadde <gajjanaga...@gmail.com>
>> >> >> >> ---
>> >> >> >> libavformat/mp3dec.c | 13 +++++++++++--
>> >> >> >> libavformat/rmdec.c | 3 ++-
>> >> >> >> 2 files changed, 13 insertions(+), 3 deletions(-)
>> >> >> >>
>> >> >> >> diff --git a/libavformat/mp3dec.c b/libavformat/mp3dec.c
>> >> >> >> index c76b21e..57ebcc8 100644
>> >> >> >> --- a/libavformat/mp3dec.c
>> >> >> >> +++ b/libavformat/mp3dec.c
>> >> >> >> @@ -372,11 +372,19 @@ static int mp3_read_header(AVFormatContext *s)
>> >> >> >> uint32_t header, header2;
>> >> >> >> int frame_size;
>> >> >> >> if (!(i&1023))
>> >> >> >> - ffio_ensure_seekback(s->pb, i + 1024 + 4);
>> >> >> >> + if ((ret = ffio_ensure_seekback(s->pb, i + 1024 + 4))
>> >> >> >> < 0) {
>> >> >> >> + av_log(s, AV_LOG_WARNING,
>> >> >> >> + "initial junk detection and skipping
>> >> >> >> impossible due to: %s\n", av_err2str(ret));
>> >> >> >> + goto skip_fail;
>> >> >> >> + }
>> >> >> >> frame_size = check(s->pb, off + i, &header);
>> >> >> >> if (frame_size > 0) {
>> >> >> >> avio_seek(s->pb, off, SEEK_SET);
>> >> >> >> - ffio_ensure_seekback(s->pb, i + 1024 + frame_size + 4);
>> >> >> >> + if ((ret = ffio_ensure_seekback(s->pb, i + 1024 +
>> >> >> >> frame_size + 4)) < 0) {
>> >> >> >> + av_log(s, AV_LOG_WARNING,
>> >> >> >> + "initial junk detection and skipping
>> >> >> >> impossible due to: %s\n", av_err2str(ret));
>> >> >> >> + goto skip_fail;
>> >> >> >> + }
>> >> >> >> if (check(s->pb, off + i + frame_size, &header2) >= 0
>> >> >> >> &&
>> >> >> >> (header & SAME_HEADER_MASK) == (header2 &
>> >> >> >> SAME_HEADER_MASK))
>> >> >> >> {
>> >> >> >> @@ -387,6 +395,7 @@ static int mp3_read_header(AVFormatContext *s)
>> >> >> >> }
>> >> >> >> avio_seek(s->pb, off, SEEK_SET);
>> >> >> >> }
>> >> >> >> +skip_fail:
>> >> >> >>
>> >> >> >> // the seek index is relative to the end of the xing vbr
>> >> >> >> headers
>> >> >> >> for (i = 0; i < st->nb_index_entries; i++)
>> >> >> >> diff --git a/libavformat/rmdec.c b/libavformat/rmdec.c
>> >> >> >> index 4e46a3d..470e227 100644
>> >> >> >> --- a/libavformat/rmdec.c
>> >> >> >> +++ b/libavformat/rmdec.c
>> >> >> >> @@ -618,7 +618,8 @@ static int rm_read_header(AVFormatContext *s)
>> >> >> >> size = avio_rb32(pb);
>> >> >> >> codec_pos = avio_tell(pb);
>> >> >> >>
>> >> >> >> - ffio_ensure_seekback(pb, 4);
>> >> >> >> + if ((ret = ffio_ensure_seekback(pb, 4)) < 0)
>> >> >> >> + av_log(s, AV_LOG_WARNING, "seeking back impossible
>> >> >> >> due to: %s\n", av_err2str(ret));
>> >> >> >> v = avio_rb32(pb);
>> >> >> >> if (v == MKBETAG('M', 'L', 'T', 'I')) {
>> >> >> >> ret = rm_read_multi(s, s->pb, st, mime);
>> >> >> >
>> >> >> > I maintain that this should not be done, because it makes the code
>> >> >> > verbose for no reason.
>> >> >>
>> >> >> Michael has pointed out that when seekback fails, one should really
>> >> >> break out of the junk detection loop in mp3dec. Your idea fails to
>> >> >> achieve it.
>> >> >
>> >> > Why? It's not really harmful. You could even argue that this will make
>> >> > the common case (skipping jumk and finding a valid frame in a seekable
>> >> > file) work in low memory situations, while your patch breaks it.
>> >
>> > ffio_ensure_seekback() never fails for seekable files
>> > it checks s->seekable and return 0 if true before attempting to
>> > allocate anything
>> >
>> >
>> >>
>> >> I assumed Michael had a good reason for it, but from what you say here
>> >> and my examination just now, I would at a first glance agree with you.
>> >> Ronald had concerns about repetition of messages, so if he (and
>> >> Michael) are fine with logging within ffio_ensure_seekback, then I
>> >> will log it there.
>> >
>> > as the code is written currently, if ffio_ensure_seekback() fails
>> > and that being ignored, the url_seek() to return to the begin will
>> > fail too quite likely while forward seeks will succeed.
>> > this would result in random amounts of data to be lost at the begin
>> > of the file
>> > it may print errors or warnings if such are added but nothing (like
>> > the applications return code) would indicate a problem, the user though
>> > could end with a output file that is missing the first few seconds of
>> > audio.
>> >
>> > if we break out on a ffio_ensure_seekback() failure then problems
>> > might still occur on files that have junk at te begin but files that
>> > do not have junk (which is what a valid file should look like)
>> > should work fine
>>
>> Maybe, but many mp3's streamed over http have junk at the beginning,
>> so such broken files are not rare.
>
> what kind of junk is that ?
> the mp3 code should resync on its own very quickly if its started
Seems to resync very quickly. It was not really a problem, just gave
as an illustration of junk occurence.
> from a wrong byte offset
> OTOH failure to seekback would loose several seconds of audio i
> suspect
Seems to be the case, if you are interested this is a sample stream I
was referring to: http://stream.radiosai.net:8008.
>
> do you have an example file where (if the backward url_seek is
> commented out the) the results are better with the loop executed
> than without ?
Sorry, I see only an avio_seek here in lavf/mp3dec. Can you please
point out the exact line? Alternatively it may be easier for you to
test with this link as you understand the code better.
>
>
> [...]
>
> --
> Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> Democracy is the form of government in which you can choose your dictator
>
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