[FFmpeg-devel] [PATCH] Fixes avcodec_find_best_pix_fmt() with more than 64 pix fmts defined

Michael Niedermayer michaelni at gmx.at
Sun Aug 21 18:09:39 CEST 2011


On Sat, Aug 20, 2011 at 05:06:45PM -0400, Matthew Einhorn wrote:
> On Fri, Aug 19, 2011 at 6:22 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
> > On Wed, Aug 17, 2011 at 08:50:50PM -0400, Matthew Einhorn wrote:
> >> On Wed, Aug 17, 2011 at 9:32 AM, Michael Niedermayer <michaelni at gmx.at> wrote:
> >> > On Wed, Aug 17, 2011 at 10:43:34AM +0200, Stefano Sabatini wrote:
> >> >> On date Wednesday 2011-08-17 02:38:37 -0400, Matthew Einhorn encoded:
> >> >> > Hi,
> >> >> >
> >> >> > As stated, this patch (attached) should fix
> >> >> > avcodec_find_best_pix_fmt() so that now with more than 64 pix fmts,
> >> >> > the function should be able to work for the first 64 fmts. Currently
> >> >> > the function returns a bad formats, for example,
> >> >> > avcodec_find_best_pix_fmt(1ULL << PIX_FMT_GRAY8, PIX_FMT_YUV420P, 0,
> >> >> > &nLoss) returns 72 instead of 8.
> >> >> >
> >> >> > Please be gentle as this is the first time I used git or submitted a
> >> >> > patch. If this works fine I'll try to submit a patch for a second
> >> >> > avcodec_find_best_pix_fmt_alt function that'll support more than 64
> >> >> > formats as input to the function.
> >> >>
> >> >> You're welcome. And yes I agree we should replace the function with a
> >> >> sane variant, for example:
> >> >>
> >> >> enum PixelFormat avcodec_find_best_pix_fmt2(int *pix_fmts, int pix_fmts_nb,
> >> >>                                             enum PixelFormat src_pix_fmt, ...);
> >> >>
> >> >> you pass a list of pixel formats (specifying the size, or
> >> >> alternatively setting the last element to -1), no hardcoded limit on
> >> >> the number of pixel formats.
> >> >
> >> > depending on how its used it might be simpler to have a function
> >> > comparing 2 pixel formats
> >> > int is_better_pix_fmt(enum PixelFormat *best, enum PixelFormat try,
> >> >                      enum PixelFormat src_pix_fmt, ...);
> >> >
> >> > That would avoid having to build the array if it has to be build
> >> >
> >> That makes sense, however, the function (patch attached) should have
> >> more than one destination
> >> pixel format to choose from. The reason is that we already have a
> >> avcodec_get_pix_fmt_loss() function
> >> that could be used to find which pixel format is better as compared to another.
> >> avcodec_find_best_pix_fmt() is typically used when you have a source
> >> and multiple destination formats and you
> >> like to find the best destination format, in that case comparing the
> >> source to a single dest pixel fmt won't be helpful
> >> directly because you want to compare multiple destination formats in
> >> the "context" of the source format. I think the function
> >> added in the patch solves that.
> >>
> >> See in the documentation of the function (in the patch) how this would
> >> allow to find the best pixel format from a list of formats.
> >>
> >>
> >> In addition, the function allows the user to select which type of loss
> >> is acceptable to them (loss_ptr) and they aren't locked in to the
> >> losses as enumerated
> >> in the loss_mask_order array.
> >>
> >> Also, I didn't change the loss_mask_order array that enumerates losses
> >> in increasing order. However, should that be edited? I'm not sure
> >> why that order was selected, but I guess now is a good time as any to
> >> look at that and possibly improve/increase that array? I don't know
> >> much
> >> about pix fmts so I don't know if that's already prefect.
> >>
> >> Thanks for the application of the previous patch,
> >> Matt
> >>
> >> >
> >> >>
> >> >> >
> >> >> > Thanks,
> >> >> > Matt
> >> >>
> >> >> > From 076c8f936a46ea42cd4242eb4df2db265653d972 Mon Sep 17 00:00:00 2001
> >> >> > From: Matthew Einhorn <moiein2000 at gmail.com>
> >> >> > Date: Wed, 17 Aug 2011 01:58:33 -0400
> >> >> > Subject: [PATCH] Fixes avcodec_find_best_pix_fmt() when there's more than 64
> >> >> >  pixel formats.
> >> >> >
> >> >> > This fixed the problem where if there's more than 64 pixel formats defined
> >> >> > avcodec_find_best_pix_fmt() returns the wrong pixel format.
> >> >> >
> >> >> > Signed-off-by: Matthew Einhorn <moiein2000 at gmail.com>
> >> >> > ---
> >> >> >  libavcodec/avcodec.h    |    4 +++-
> >> >> >  libavcodec/imgconvert.c |    2 +-
> >> >> >  2 files changed, 4 insertions(+), 2 deletions(-)
> >> >> >
> >> >> > diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
> >> >> > index 4f0ed2d..f7d1520 100644
> >> >> > --- a/libavcodec/avcodec.h
> >> >> > +++ b/libavcodec/avcodec.h
> >> >> > @@ -3496,9 +3496,11 @@ int avcodec_get_pix_fmt_loss(enum PixelFormat dst_pix_fmt, enum PixelFormat src_
> >> >> >   * The pixel formats from which it chooses one, are determined by the
> >> >> >   * pix_fmt_mask parameter.
> >> >> >   *
> >> >> > + * Note, only the first 64 pixel formats will fit in pix_fmt_mask
> >> >> > + *
> >> >> >   * @code
> >> >> >   * src_pix_fmt = PIX_FMT_YUV420P;
> >> >> > - * pix_fmt_mask = (1 << PIX_FMT_YUV422P) || (1 << PIX_FMT_RGB24);
> >> >> > + * pix_fmt_mask = (1 << PIX_FMT_YUV422P) | (1 << PIX_FMT_RGB24);
> >> >> >   * dst_pix_fmt = avcodec_find_best_pix_fmt(pix_fmt_mask, src_pix_fmt, alpha, &loss);
> >> >> >   * @endcode
> >> >> >   *
> >> >> > diff --git a/libavcodec/imgconvert.c b/libavcodec/imgconvert.c
> >> >> > index 9efed50..a4197cb 100644
> >> >> > --- a/libavcodec/imgconvert.c
> >> >> > +++ b/libavcodec/imgconvert.c
> >> >> > @@ -439,7 +439,7 @@ static enum PixelFormat avcodec_find_best_pix_fmt1(int64_t pix_fmt_mask,
> >> >> >      /* find exact color match with smallest size */
> >> >> >      dst_pix_fmt = PIX_FMT_NONE;
> >> >> >      min_dist = 0x7fffffff;
> >> >> > -    for(i = 0;i < PIX_FMT_NB; i++) {
> >> >> > +    for(i = 0;i < FFMIN(PIX_FMT_NB, 64); i++) {
> >> >> >          if (pix_fmt_mask & (1ULL << i)) {
> >> >> >              loss = avcodec_get_pix_fmt_loss(i, src_pix_fmt, has_alpha) & loss_mask;
> >> >> >              if (loss == 0) {
> >> >>
> >> >> Looks fine to me, I'm going to apply soon if I read no comments (maybe
> >> >> Michael?).
> >> >
> >> > LGTM
> >> >
> >> > [...]
> >> > --
> >> > Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
> >> >
> >> > Observe your enemies, for they first find out your faults. -- Antisthenes
> >> >
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> >> >
> >> > _______________________________________________
> >> > ffmpeg-devel mailing list
> >> > ffmpeg-devel at ffmpeg.org
> >> > http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
> >> >
> >> >
> >
> >>  avcodec.h    |   34 ++++++++++++++++++++++++++++++++++
> >>  imgconvert.c |   46 ++++++++++++++++++++++++++++++++++++++++++++++
> >>  2 files changed, 80 insertions(+)
> >> a2185b7288f78de01eaf39b89f5de1d313643607  0001-Adds-a-new-pix-fmt-function-that-selects-the-best-de.patch
> >> From a873e791be7802b110ac44e279b904d28e2e2fb4 Mon Sep 17 00:00:00 2001
> >> From: Matthew Einhorn <moiein2000 at gmail.com>
> >> Date: Wed, 17 Aug 2011 20:14:54 -0400
> >> Subject: [PATCH] Adds a new pix fmt function that selects the best dest fmt
> >>  from among 2 formats to convert to, given a certain src
> >>  format.
> >>
> >> Similar to avcodec_find_best_pix_fmt(), but instead only compares two destination
> >> pix fmts and selects one of these fmts as the best dest format when converting from
> >> a given source format. Also, as opposed to avcodec_find_best_pix_fmt() which supports
> >> only the first 64 defined pixel formats, this supports as input any of the defined
> >> pixel formats.
> >>
> >> Signed-off-by: Matthew Einhorn <moiein2000 at gmail.com>
> >> ---
> >>  libavcodec/avcodec.h    |   34 ++++++++++++++++++++++++++++++++++
> >>  libavcodec/imgconvert.c |   46 ++++++++++++++++++++++++++++++++++++++++++++++
> >>  2 files changed, 80 insertions(+), 0 deletions(-)
> >
> > The old function should be replaced by the new and the old then
> > implemented by using the new
> 
> Should I implement new and re-implement old in one patch or in two patches?

both in one patch


> 
> Also, the old function makes use of an internal
> avcodec_find_best_pix_fmt1() function which is used "only" by the old
> function, can I remove that?

yes but that should be a seperate patch


> 
> Finally, the new function allows the input of PIX_FMT_NONE as a
> destination format because it would simplify the use of it (if "one"
> of the dest pix fmts can be -1) because you'd have to do less error
> checking. However, to do that avcodec_get_pix_fmt_loss() also needs to
> support the "dst_pix_fmt" parameter to be PIX_FMT_NONE (otherwise I
> need to check for it in the new function). Would it be appropriate to
> patch avcodec_get_pix_fmt_loss() to include a line of code at the
> start where if the dest format is -1 it returns the maximum loss or
> should it stay as undefined behavior (since arrays then get indexed by
> -1)?

yes, of course

[... ]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

While the State exists there can be no freedom; when there is freedom there
will be no State. -- Vladimir Lenin
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